This is like an "unloader valve" (?) - which does exist - but with
additional characteristics(?)

The need...

I've got a hypothetical on-paper hydraulic device.

For fatigue-testing
- while "the hydraulic cylinder is always bigger than the sample
you are trying to test"
* has always meant a machine with a frame and parts distributed along
a central axis, dwarfing the size of the sample it's testing
* it also means the sample will always fit *inside* the hydraulic
cylinder which is testing it

I cycled up a high hill to get that inspiration, by the way, if you
were wondering...

For fatigue testing samples - it has to tension and release millions
of times.

If I had this valve I mention, you connect the cylinder directly to a
pump - the higher its capacity the faster - more strokes per second -
it will go - "strokes per second" - with "the valve" at the outlet,
dumping the oil in the cylinder and flow of the pump for the time
being back to the tank.

The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

There are computer-controlled systems with a pressure transducer and
the "dump" valve opening on command.
These are the "servo-hydraulic" systems which are familiar to many.
That might be the option it would be necessary to use, in reality.

However - still curious if there is a stand-alone valve device which
does what's wanted.

For accurate pressure control, the only thing I could think of was to
use a balanced open-close valve (sliding "bobbin" ?) - but with one
end pressurised by a "reference pressure system" with its own small
pump, large accumulator and pressure relief valve returning to the
tank.
With the cylinder pressure routed to the other side of the "balanced
valve".
So when the cylinder pressure exceeds the reference pressure by only a
small amount, the valve moves over to rapidly fully open a big dump
line to tank.
Then there has to be another mechanism / valve which only trips for
the valve to return to closed when the cylinder pressure is about the
same as atmospheric.
If proven to work well, the almost constant pressure in the reference
system could be taken as the peak pressure the cylinder reaches.
That reference pressure is freely adjustable by turning the adjuster
squeezing the spring on the relief valve of the "reference" system.

Thanks for considering.

Rich Smith

"Richard Smith" wrote in message ...

This is like an "unloader valve" (?) - which does exist - but with
additional characteristics(?)

The need...

I've got a hypothetical on-paper hydraulic device.

For fatigue-testing
- while "the hydraulic cylinder is always bigger than the sample
you are trying to test"
* has always meant a machine with a frame and parts distributed along
a central axis, dwarfing the size of the sample it's testing
* it also means the sample will always fit *inside* the hydraulic
cylinder which is testing it

I cycled up a high hill to get that inspiration, by the way, if you
were wondering...

For fatigue testing samples - it has to tension and release millions
of times.

If I had this valve I mention, you connect the cylinder directly to a
pump - the higher its capacity the faster - more strokes per second -
it will go - "strokes per second" - with "the valve" at the outlet,
dumping the oil in the cylinder and flow of the pump for the time
being back to the tank.

The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

There are computer-controlled systems with a pressure transducer and
the "dump" valve opening on command.
These are the "servo-hydraulic" systems which are familiar to many.
That might be the option it would be necessary to use, in reality.

However - still curious if there is a stand-alone valve device which
does what's wanted.

For accurate pressure control, the only thing I could think of was to
use a balanced open-close valve (sliding "bobbin" ?) - but with one
end pressurised by a "reference pressure system" with its own small
pump, large accumulator and pressure relief valve returning to the
tank.
With the cylinder pressure routed to the other side of the "balanced
valve".
So when the cylinder pressure exceeds the reference pressure by only a
small amount, the valve moves over to rapidly fully open a big dump
line to tank.
Then there has to be another mechanism / valve which only trips for
the valve to return to closed when the cylinder pressure is about the
same as atmospheric.
If proven to work well, the almost constant pressure in the reference
system could be taken as the peak pressure the cylinder reaches.
That reference pressure is freely adjustable by turning the adjuster
squeezing the spring on the relief valve of the "reference" system.

Thanks for considering.

Rich Smith

----------------------

As I understand it, you want a bistable valve with variable hysteresis
between its opening and closing pressures.

I recently tricked up a relay for my solar panels that acts that way. Relays
do anyway but aren't adjustable, I have it switching resistance in or out of
series with the coil to set the pull-in and drop-out voltages. The reason is
to protect digital meters from the voltage range just below their minimum
supply requirement at dawn and dusk, where they operate strangely.

For your problem a second pilot cylinder could change the tension of the
relief valve spring that opposes the pressure. You might need a small
accumulator and restrictor orifice to delay the pressure change at the pilot
to ensure the valve completes each operation instead of chattering between
states.

The generic name for a bistable device with memory is "flip-flop".
https://www.hydraulicspneumatics.com...neumatic-logic

The solution is easy with electrical control by relays and solenoid valves.
You can either sense pressure or use time delays.

https://en.wikipedia.org/wiki/Relay_logic
In the example STOP/START circuit CR1 (ControlRelay1) is bistable, it
remains in whichever state the last button press left it. The symbol that
looks like a capacitor is a relay contact and the circles are relay coils,
solenoids, motors, etc.

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons

"Ned Simmons" wrote in message
...

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

Is this commercial or Heath Robinson?

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:

This is like an "unloader valve" (?) - which does exist - but with
additional characteristics(?)

The need...

I've got a hypothetical on-paper hydraulic device.

For fatigue-testing
- while "the hydraulic cylinder is always bigger than the sample
you are trying to test"
* has always meant a machine with a frame and parts distributed along
a central axis, dwarfing the size of the sample it's testing
* it also means the sample will always fit *inside* the hydraulic
cylinder which is testing it

I cycled up a high hill to get that inspiration, by the way, if you
were wondering...

For fatigue testing samples - it has to tension and release millions
of times.

If I had this valve I mention, you connect the cylinder directly to a
pump - the higher its capacity the faster - more strokes per second -
it will go - "strokes per second" - with "the valve" at the outlet,
dumping the oil in the cylinder and flow of the pump for the time
being back to the tank.

The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

This sounds very much like the mechanism of a hydraulic shake-table
driver, used for vibration testing of all kinds of equipment.

One manufacturer is Unholtz-Dickie. Look into their history, and
patents assigned to them and their predecessors.

Like "Fluid-operated vibration test exciter" to John Dickie, patent
US2773482A. This is basically a siren driving a shuttle piston back
and forth. If the shuttle piston is prevented from moving, it will
generate a cyclic stress. The addition of a dead weight to this
allows the cyclic stress to ride atop a static stress.

Joe Gwinn

"Joe Gwinn" wrote in message
...

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:

This is like an "unloader valve" (?) - which does exist - but with
additional characteristics(?)

The need...

I've got a hypothetical on-paper hydraulic device.

For fatigue-testing
- while "the hydraulic cylinder is always bigger than the sample
you are trying to test"
* has always meant a machine with a frame and parts distributed along
a central axis, dwarfing the size of the sample it's testing
* it also means the sample will always fit *inside* the hydraulic
cylinder which is testing it

I cycled up a high hill to get that inspiration, by the way, if you
were wondering...

For fatigue testing samples - it has to tension and release millions
of times.

If I had this valve I mention, you connect the cylinder directly to a
pump - the higher its capacity the faster - more strokes per second -
it will go - "strokes per second" - with "the valve" at the outlet,
dumping the oil in the cylinder and flow of the pump for the time
being back to the tank.

The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

This sounds very much like the mechanism of a hydraulic shake-table
driver, used for vibration testing of all kinds of equipment.

One manufacturer is Unholtz-Dickie. Look into their history, and
patents assigned to them and their predecessors.

Like "Fluid-operated vibration test exciter" to John Dickie, patent
US2773482A. This is basically a siren driving a shuttle piston back
and forth. If the shuttle piston is prevented from moving, it will
generate a cyclic stress. The addition of a dead weight to this
allows the cyclic stress to ride atop a static stress.

Joe Gwinn

----------------------------

I considered an oscillator-based solution but didn't suggest it because they
may require specialized instruments, dataloggers, digital storage
oscilloscopes and spectrum analyzers, to test and debug. It's much easier to
test a system that can be stopped or run slowly.

"Richard Smith" wrote in message ...
....
For fatigue testing samples - it has to tension and release millions
of times.
....
----------------------

If you want simple, a 3-port rotary valve would alternately let oil in and
out of the cylinder. You could run it slowly until you determine how fast
you can spin it and still attain full and minimum pressure. The valve could
operate a revolution or cycle counter. If you can tolerate a little leakage
it's simple enough for a model engineer to make. ( I have too many machining
jobs for the sawmill and its gantry hoist in the queue to offer. )

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
.. .

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons

Hi to everyone.
You folk are amazing!
I've been here on my own, and you come along knowing lots of solutions.
I'm in information-overload with all the great leads you've given.
Plus I've just done a week and a half of calculations on testing
methods and really really need to give my head time-out.

You asked about this device.
I'll share with you
http://www.weldsmith.co.uk/tech/fatg...hyd_inner.html
It's an idea for a metal fatigue test, particularly of welds.

So in this rig, the sample is inaccessible, inside the hydraulic
cylinder immersed in the hydraulic fluid.

For the advantages you get, the disadvantages are "nothing".
This test could be running for days to 10's of days, by the way.
It's "high stakes".

Even where you can stop the test and approach the sample, you don't,
in reality. Gets you nothing additional.

The test stops when the sample breaks...

Welding the sample to the "pistons" has more advantages than
disadvantages (one would reckon).
Small and stiff.

A "contraption"? Yes. However - so long as you do a "scattergun"
approach, you have a significant likelihood that some try will work.
You have to be very open-minded, because you can have "dead-certs"
which don't work, and "shouldn't work" which delivers and then some.
You can find the science was wrong, or incomplete, and by giving it a
try anyway you find that out, as well as getting results.

I'll get my head around the info - the links and hints.

Like be back in a little while...

Best wishes all,
Rich S

Ned Simmons writes:

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
. ..

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons

Ned - I thought this is it.

Then I realised (?) - the full flow of the pump will always be the
minimum flowing through valve - which will defeat the closing action
we are counting on? This device, the "kickdown valve", is for filling
say a hydraulic cylinder, where the flow comes to a definitive stop at
full stroke? It avoid the energy loss of pumping oil past in-effect
an "intermediate-pressure" relief valve.

I suspect that constant flow from the pump would defeat it ??

I'll try to do sketches.

I have thought of a circuit I believe would act quickly at the set
pressure - giving the set pressure and no more. I ran with the idea
of having "separate reference pressure system" where a small pump,
large accumulator and pressure in it freely set via an adjustable
pressure relief valve dumping back to the reference-system tank. I'll
try to sketch that too.

Rich S

"Jim Wilkins" writes:

"Joe Gwinn" wrote in message
...

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:

This is like an "unloader valve" (?) - which does exist - but with
additional characteristics(?)

The need...

I've got a hypothetical on-paper hydraulic device.

For fatigue-testing
- while "the hydraulic cylinder is always bigger than the sample
you are trying to test"
* has always meant a machine with a frame and parts distributed along
a central axis, dwarfing the size of the sample it's testing
* it also means the sample will always fit *inside* the hydraulic
cylinder which is testing it

I cycled up a high hill to get that inspiration, by the way, if you
were wondering...

For fatigue testing samples - it has to tension and release millions
of times.

If I had this valve I mention, you connect the cylinder directly to a
pump - the higher its capacity the faster - more strokes per second -
it will go - "strokes per second" - with "the valve" at the outlet,
dumping the oil in the cylinder and flow of the pump for the time
being back to the tank.

The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

This sounds very much like the mechanism of a hydraulic shake-table
driver, used for vibration testing of all kinds of equipment.

One manufacturer is Unholtz-Dickie. Look into their history, and
patents assigned to them and their predecessors.

Like "Fluid-operated vibration test exciter" to John Dickie, patent
US2773482A. This is basically a siren driving a shuttle piston back
and forth. If the shuttle piston is prevented from moving, it will
generate a cyclic stress. The addition of a dead weight to this
allows the cyclic stress to ride atop a static stress.

Joe Gwinn

----------------------------

I considered an oscillator-based solution but didn't suggest it
because they may require specialized instruments, dataloggers, digital
storage oscilloscopes and spectrum analyzers, to test and debug. It's
much easier to test a system that can be stopped or run slowly.

That's a "vibrophore", isn't it, if you apply that conept ot fatigue
testing machines?

Electro-mechanical device.

You would always use one of these if you could, for the project I'm
planning (?) Test rates to 150Hz and higher. Energy consumption so low
many will plug into a "domestic" wall socket.

Never met one in real life. Would desperately like to.
Idea of running a sample to 20 Million cycles no problem is like a
dream come true.

But the problem is when you go beyond "research test samples" to
testing representations of full-sized welds.

The biggest machines are 100Tonnes-force (1000kN; 1MN).

I've indicated the discussions would get very favourable if a 250kN
(25Tonne-force) "vibrophore" were available.

The rig I've sketched is for if say you needed to test a weld to
hundreds of tonnes cyclic stress range.

Rich S

"Ned Simmons" wrote in message
...

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
.. .

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons
-----------------------------------

I'll take your expert word for it. My brain is still in a primitive BC
state. (Before Coffee)
https://www.hydraulicspneumatics.com...equence-valves

"When flow stops, spring force closes the main poppet because pressure has
equalized."

"Richard Smith" wrote in message ...
....
You asked about this device.
I'll share with you
http://www.weldsmith.co.uk/tech/fatg...hyd_inner.html
It's an idea for a metal fatigue test, particularly of welds.

So in this rig, the sample is inaccessible, inside the hydraulic
cylinder immersed in the hydraulic fluid.

For the advantages you get, the disadvantages are "nothing".
This test could be running for days to 10's of days, by the way.
It's "high stakes".
---------------------------

You might be able to significantly reduce the 80KW power demand if the
pressure source is a small flywheel-driven piston built into the fixed end
of the cylinder to minimize flow friction loss, that absorbs the pressure
energy as it retracts. You'd add oil/bleed air until a pressure sensor
signal peaks at the desired pressure.

This could require some custom machining and knowledge of using an
oscilloscope. Are those acceptable for you?

When I was in the automated testing business we had to figure times for high
count operations such as testing each cell on a memory chip wafer, often in
conversation without a calculator. There are 86,400 seconds in a day. 1
million seconds (cycles?) is 11.57 days. A micro-year is 31.5 seconds. 1 US
billion (10^9) seconds is 31.7 years.

https://www.youtube.com/watch?v=hj7LRuusFqo

"Jim Wilkins" writes:

"Richard Smith" wrote in message ...
...
You asked about this device.
I'll share with you
http://www.weldsmith.co.uk/tech/fatg...hyd_inner.html
It's an idea for a metal fatigue test, particularly of welds.

So in this rig, the sample is inaccessible, inside the hydraulic
cylinder immersed in the hydraulic fluid.

For the advantages you get, the disadvantages are "nothing".
This test could be running for days to 10's of days, by the way.
It's "high stakes".
---------------------------

You might be able to significantly reduce the 80KW power demand if the
pressure source is a small flywheel-driven piston built into the fixed
end of the cylinder to minimize flow friction loss, that absorbs the
pressure energy as it retracts. You'd add oil/bleed air until a
pressure sensor signal peaks at the desired pressure.

This could require some custom machining and knowledge of using an
oscilloscope. Are those acceptable for you?

When I was in the automated testing business we had to figure times
for high count operations such as testing each cell on a memory chip
wafer, often in conversation without a calculator. There are 86,400
seconds in a day. 1 million seconds (cycles?) is 11.57 days. A
micro-year is 31.5 seconds. 1 US billion (10^9) seconds is 31.7 years.

https://www.youtube.com/watch?v=hj7LRuusFqo

Exactly so.

I have already done these calculations for my "beam configuration"
fatigue test.
Static version of it - tensile test
http://www.weldsmith.co.uk/tech/stru...t_testrig.html

The benefit you have there are the highly predictable Euler-Bernoulli
beam calculations for long sections.
I found one fixed stroke actuator would cover every need.


The problem with the "hydraulic inner fatigue test" is it is difficult
to know with much accuracy how much hydraulic oil it is going to take
per stroke to reach the intended force on the sample.
The end pistons seem to be the design challenge. Flexing. Cylinder
analysed by "hoop stress" no problem.

Also - adjusting it so you can arrive at different forces...
Because you need to explore the shape of the fatigue "S-N curve".

That's why took thought of servo-hydraulic.
With "catalog" equipment you could quickly get started.
Connect it up and off you go.
You'd probably use a pressure transducer and servo valves, wth digital
logic linking them. In reality. As the equipment would be already
there and familiar.

I've drawn the servo-hydraulic drive system.
Mechanical logic though.
Drawn as best I can.
Sorry about any offence to familiar conventions.

http://www.weldsmith.co.uk/tech/fatg...-hyd_drive.pdf

There's two "bobbin" valves.

The big one dumps the main power system oil to the tank.
It opens when the cylinder pressure exceeds the reference pressure.
That cylinder oil comes through a check-valve, so once pressurised and
vlave open, it stays open.
Until...
The other "bobbin" valve opens when the cylinder pressure is so low it
cannot overcome a spring - that opening dumping the ex cylinder
pressure holding open the main bobbin valve against the reference
pressure - that reference pressure reopening the main valve.

All this mechanism could be on one "pallet" - reference system and
power system adjacent, with one pipe to the test-rig atking
back-and-forth flows.

Sorry that's "reference pressure re-closes the main valve" - to start the next cycle.

It would be good if this system could cycle very quickly and the bigger the pump, the faster it cycles.

On Wed, 19 May 2021 17:42:41 -0400, "Jim Wilkins"
wrote:

"Joe Gwinn" wrote in message
.. .

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:

[snip]

Like "Fluid-operated vibration test exciter" to John Dickie, patent
US2773482A. This is basically a siren driving a shuttle piston back
and forth. If the shuttle piston is prevented from moving, it will
generate a cyclic stress. The addition of a dead weight to this
allows the cyclic stress to ride atop a static stress.

Joe Gwinn

----------------------------

I considered an oscillator-based solution but didn't suggest it because they
may require specialized instruments, dataloggers, digital storage
oscilloscopes and spectrum analyzers, to test and debug. It's much easier to
test a system that can be stopped or run slowly.

In the patent reference above, the oscillation cycle is controlled by
an external "variable speed motor" of unspecified kind, designated is
item 25 in the figures and accompanying text.

If the motor runs slow, so does the oscillation cycle, in direct
proportion.

Joe Gwinn

there's other errors.
Reference pressure must hold main dump valve closed, until cylinder pressure exceeds refernce pressure.
Sure there will be other errors.
Got to head off now. Thanks for everything
Rich S

"Joe Gwinn" wrote in message
...
....
If the motor runs slow, so does the oscillation cycle, in direct
proportion.

Joe Gwinn
----------------------
If the expected fatigue life is 2 million cycles, the test time at 1 cycle
per second is three weeks. I think a good solution would be a closed loop
based on a pressure sensor that shows when the high and low limit pressures
have been reached, so the controller can switch between the fill and dump
solenoid valves as rapidly as fluid flow permits.

If I had to build a prototype of the tester the controller would be an old
laptop (or desktop) with a printer port, the data bits driving a
successive-approximation A/D converter to measure the pressure sensor and
two control bits operating the fill and dump solenoid valves.

QBasic running in DOS gives full unhindered access to all of the printer
port bits for input and output, unlike Windows. An Arduino could also work
but the laptop has the advantages of a huge hard drive to store data, the
keyboard for control, and the LCD on which QBasic can display the cycle
count and a graph of the pressure.
http://www.nicolasbize.com/blog/30-y...till-the-best/

This simple resistor network outputs a voltage proportional to the binary
code from the port bits:
https://www.tek.com/blog/tutorial-di...rsion-r-2r-dac

The other electronics are an analog comparator (LM311) driving a printer
port status bit that tells if the sensor output voltage is more or less than
the DAC output, and the two high current solenoid valve drivers.

On Thu, 20 May 2021 12:01:50 +0100, Richard Smith
wrote:

Ned Simmons writes:

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
...

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons

Ned - I thought this is it.

Then I realised (?) - the full flow of the pump will always be the
minimum flowing through valve - which will defeat the closing action
we are counting on? This device, the "kickdown valve", is for filling
say a hydraulic cylinder, where the flow comes to a definitive stop at
full stroke? It avoid the energy loss of pumping oil past in-effect
an "intermediate-pressure" relief valve.

I suspect that constant flow from the pump would defeat it ??

Good question, but I don't think so, as long as the valve and the
return piping are sized such that the pressure at the OUT port (at
full flow) is low enough that the "light spring" in Fig 2 can force
the spool closed.

In other words: the pressure rises to the set point; the "control
relief poppet" opens, releasing the balancing pressure on the back
side of the main spool; the spool shifts open, and the pressure at the
IN port drops; the control poppet closes, but; the "kickdown jet" is
now open and bleeds the balancing pressure from the back of the spool,
until; delta P across the spool * spool area spring force and the
valve closes.

I hope that's right. Whether this is a practical way to control your
device in the real world is another matter.


I'll try to do sketches.

I have thought of a circuit I believe would act quickly at the set
pressure - giving the set pressure and no more. I ran with the idea
of having "separate reference pressure system" where a small pump,
large accumulator and pressure in it freely set via an adjustable
pressure relief valve dumping back to the reference-system tank. I'll
try to sketch that too.

Rich S

--
Ned Simmons

On Thu, 20 May 2021 07:22:42 -0400, "Jim Wilkins"
wrote:

"Ned Simmons" wrote in message
.. .

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
. ..

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons
-----------------------------------

I'll take your expert word for it. My brain is still in a primitive BC
state. (Before Coffee)
https://www.hydraulicspneumatics.com...equence-valves

"When flow stops, spring force closes the main poppet because pressure has
equalized."


I don't entirely follow that paragraph. See my reply to Richard.

Re a device with memory, a directional valve with two detented
solenoid actuators would do the trick. One solenoid controlled by a
pressure switch that closes at the high pressure setting, the other by
a pressure switch that closes at the low pressure setting. Or the
hydraulic equivalent.

https://www.festo-didactic.com/int-e...i4xMjMxLjY3Nzk

--
Ned Simmons

"Jim Wilkins" writes:

"Joe Gwinn" wrote in message
...
...
If the motor runs slow, so does the oscillation cycle, in direct
proportion.

Joe Gwinn
----------------------
If the expected fatigue life is 2 million cycles, the test time at 1
cycle per second is three weeks. I think a good solution would be a
closed loop based on a pressure sensor that shows when the high and
low limit pressures have been reached, so the controller can switch
between the fill and dump solenoid valves as rapidly as fluid flow
permits.

If I had to build a prototype of the tester the controller would be an
old laptop (or desktop) with a printer port, the data bits driving a
successive-approximation A/D converter to measure the pressure sensor
and two control bits operating the fill and dump solenoid valves.

QBasic running in DOS gives full unhindered access to all of the
printer port bits for input and output, unlike Windows. An Arduino
could also work but the laptop has the advantages of a huge hard drive
to store data, the keyboard for control, and the LCD on which QBasic
can display the cycle count and a graph of the pressure.
http://www.nicolasbize.com/blog/30-y...till-the-best/

This simple resistor network outputs a voltage proportional to the
binary code from the port bits:
https://www.tek.com/blog/tutorial-di...rsion-r-2r-dac

The other electronics are an analog comparator (LM311) driving a
printer port status bit that tells if the sensor output voltage is
more or less than the DAC output, and the two high current solenoid
valve drivers.

Stunning detail.
I see that with
* test method and hardware
* control and data acquisition
2million cycles would be a start. With well-performing welds, you'd
want to get out to 20million cycles or more
(200Million is something around what a ship or bridge gets in its
entire period of service, but can be a bit of an ask in test).
I've programmed in Basic. Access to devices / ports - hadn't thought
about it being that convenient and tailor-made.

Ned, Jim, everyone - massive thanks. Rich S

"Richard Smith" wrote in message ...
....
I've programmed in Basic. Access to devices / ports - hadn't thought
about it being that convenient and tailor-made.

----------------------

I can't claim credit for the idea, it was the engineer's suggestion when we
(Unitrode / Texas Instruments) wanted to design and operate evaluation
boards for new user-configurable ICs from customers' unmodified laboratory
computers, which at the time were typically former office desktops and
laptops running Win98. We started with Visual Basic but quickly found that
it lacks the hardware control instructions of QBasic, and Windows polls the
printer port to detect newly attached devices. DOS + QB give full read/write
access to the I/O address space, interrupted only to update the clock.

The only change to the computer was setting the BIOS to boot from a DOS
floppy if present, else to Windows. The same can be done with a USB flash
drive using HPUSBFW. FAT32 USB flash drives are big enough to store programs
and large data files without access to the NTFS internal drive though older
FAT32 hard drives could handle either DOS or Windows, up through XP.
https://www.handheldgroup.com/knowle...ble-usb-drive/

The computer boots normally with the flash drive removed and you can read
any data log files the QB program created, such as cycle intervals which
might increase when the sample began to stretch, and indicate the point of
failure if you can't otherwise sense it.

I had previously assembled one-time computer to hardware interfaces with
added plug-in boards, a purchased digital I/O card and a 16 bit A/D
converter for the Macintosh that I designed. The printer port and DOS/QB
method turned out to be easier for relatively simple tasks. I'm also very
familiar with relay ladder logic controls if you choose to go that way.

Do you have the equipment or machinist friends to consider custom machining
as part of solutions? I couldn't do nearly as much without my lathe and
milling machine.

"Jim Wilkins" writes:

"Richard Smith" wrote in message ...
...
I've programmed in Basic. Access to devices / ports - hadn't thought
about it being that convenient and tailor-made.

----------------------

I can't claim credit for the idea, it was the engineer's suggestion
when we (Unitrode / Texas Instruments) wanted to design and operate
evaluation boards for new user-configurable ICs from customers'
unmodified laboratory computers, which at the time were typically
former office desktops and laptops running Win98. We started with
Visual Basic but quickly found that it lacks the hardware control
instructions of QBasic, and Windows polls the printer port to detect
newly attached devices. DOS + QB give full read/write access to the
I/O address space, interrupted only to update the clock.

The only change to the computer was setting the BIOS to boot from a
DOS floppy if present, else to Windows. The same can be done with a
USB flash drive using HPUSBFW. FAT32 USB flash drives are big enough
to store programs and large data files without access to the NTFS
internal drive though older FAT32 hard drives could handle either DOS
or Windows, up through XP.
https://www.handheldgroup.com/knowle...ble-usb-drive/

The computer boots normally with the flash drive removed and you can
read any data log files the QB program created, such as cycle
intervals which might increase when the sample began to stretch, and
indicate the point of failure if you can't otherwise sense it.

I had previously assembled one-time computer to hardware interfaces
with added plug-in boards, a purchased digital I/O card and a 16 bit
A/D converter for the Macintosh that I designed. The printer port and
DOS/QB method turned out to be easier for relatively simple tasks. I'm
also very familiar with relay ladder logic controls if you choose to
go that way.

Do you have the equipment or machinist friends to consider custom
machining as part of solutions? I couldn't do nearly as much without
my lathe and milling machine.

Machining, making parts and equipment... My cider-maker / cider
supplier could feature in that... Can see a need to trade favours...


Digression into computing.
I often put "emacs" on a CD-ROM, take it by IT-support and invite them
to check it (fully up-to-date virus check software, etc, etc.)
If it's a write-once CD-ROM, it can't be altered ever again.
So if they trust that is all I will ever put in the drive of "my"
networked computer, that's sound in terms of IT security.

The reason for this is;
I have a range of suites of functions for various engineering
tasks which run in the test-processor I am using now - the famous /
well-known "emacs".
They will inject the answer straight into the document you are
writing. You can quote the function and the values you fed to it, and
the answer it gave. Complete record.
"sketching" your way to often high-value decisions.
Plus I do most other text-based thing in emacs.
For examples I didn't just type
"
Thermo-Mechanically Controlled-Processed High-Strength Low-Alloy
"
I typed tmcpqc hslaqc
When you are typing documents with huge strings of standard quotes of
Standards, Company Specifications, etc, that can save a huge amount of
time and effort, and leave your mind clear to think of the big
picture.
Boot off a CD-ROM? Could do?

Ned Simmons writes:

On Thu, 20 May 2021 12:01:50 +0100, Richard Smith
wrote:

Ned Simmons writes:

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
m...

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons

Ned - I thought this is it.

Then I realised (?) - the full flow of the pump will always be the
minimum flowing through valve - which will defeat the closing action
we are counting on? This device, the "kickdown valve", is for filling
say a hydraulic cylinder, where the flow comes to a definitive stop at
full stroke? It avoid the energy loss of pumping oil past in-effect
an "intermediate-pressure" relief valve.

I suspect that constant flow from the pump would defeat it ??

Good question, but I don't think so, as long as the valve and the
return piping are sized such that the pressure at the OUT port (at
full flow) is low enough that the "light spring" in Fig 2 can force
the spool closed.

In other words: the pressure rises to the set point; the "control
relief poppet" opens, releasing the balancing pressure on the back
side of the main spool; the spool shifts open, and the pressure at the
IN port drops; the control poppet closes, but; the "kickdown jet" is
now open and bleeds the balancing pressure from the back of the spool,
until; delta P across the spool * spool area spring force and the
valve closes.

I hope that's right. Whether this is a practical way to control your
device in the real world is another matter.


I'll try to do sketches.

I have thought of a circuit I believe would act quickly at the set
pressure - giving the set pressure and no more. I ran with the idea
of having "separate reference pressure system" where a small pump,
large accumulator and pressure in it freely set via an adjustable
pressure relief valve dumping back to the reference-system tank. I'll
try to sketch that too.

Rich S

--
Ned Simmons

Hi Ned.

Your real-world experience enables you to answer this question?

You've already raised the point

"... Whether this is a practical way to control your device in the real
world is another matter."

I was thinking of constancy of pressure at which it triggers.
This thing is perfect when sequencing.
For a fatigue test, hydraulic pressure at trigger = peak force.
This is crucial to the test - for the peak force to be known and constant.
Would this device settle down to triggering at a very constant
pressure, do you reckon?
Within reason, so long as it stays constant, what that pressure is is
just fine - plot the "F=PA" force on the "S-N curve / plot" for
comparability of data.

(That's why I designed a parallel small system "reference pressure"
concept - so the peak force / pressure is accurately at, but neither
more or less, than a constant reference pressure)

Rich Smith

"Richard Smith" wrote in message ...

"Jim Wilkins" writes:
....
Do you have the equipment or machinist friends to consider custom
machining as part of solutions? ...

Machining, making parts and equipment... My cider-maker / cider
supplier could feature in that... Can see a need to trade favours...

-----------
So not easily, perhaps shortening a bolt but not to the full custom extent I
would otherwise suggest, like the small piston in the cylinder end cap.
Experimenting is difficult when you are limited to only what you can afford
to buy. My shop is what an inventor would have dreamed of in 1960 though
perhaps not today, after 50~60 years of wear.

How about electronic test equipment? Capturing the brief peak value from an
analog pressure sensor during rapid cycling will be difficult without a
digital storage oscilloscope.

https://www.aliexpress.com/price/200...sor_price.html

"Richard Smith" wrote in message ...
Ned Simmons writes:

....
This is crucial to the test - for the peak force to be known and constant.
Would this device settle down to triggering at a very constant
pressure, do you reckon?

-----------------

I don't know about that valve but I do have lots of R&D experience on
difficult projects.

Generally you design and build what you predict (hope) will work, then
measure and correct until you run out of time, money or patience, and
declare it "good enough". The limit is how accurately you can measure.

If the valve is inconsistent you may simply need a better filter, or
different oil viscosity. A recording of cycle intervals and peak pressures
would show you if a problem develops and perhaps hint at why, i.e. was the
change sudden or gradual.

I save measurement data into text files that can be loaded into a
spreadsheet as *.csv for analysis.

"Richard Smith" wrote in message ...
...
Boot off a CD-ROM? Could do?

_____________
Can do easily.

Hit the key during startup that enters the BIOS setup and put the CD-ROM
ahead of the hard drive in the Boot Sequence. On my Dells it's F2 before the
self-test completes. F12 lets me select any bootable source for this session
only.

My Lenovo laptop is a little different. It came in a Fastboot mode that
bypassed the chance to enter the BIOS.
https://support.lenovo.com/us/en/sol...n-windows-1081

On Fri, 21 May 2021 16:05:45 +0100, Richard Smith
wrote:

Ned Simmons writes:

On Thu, 20 May 2021 12:01:50 +0100, Richard Smith
wrote:

Ned Simmons writes:

On Wed, 19 May 2021 12:43:21 -0400, "Jim Wilkins"
wrote:

Ned Simmons" wrote in message
om...

On Wed, 19 May 2021 07:18:38 +0100, Richard Smith
wrote:



The set pressure of opening means you reach an aim maximum tension in
the sample.
That that valve stays fully open until the hydraulic pressure drops to
(very near) zero completely unloads the sample to no load.
The valve closes and the cycle repeats, etc.

Does such a valve exist?

Look at "sequence valves."

For example:
http://valveproducts.net/pressure-se...sequence-valve


Rich Smith

--
Ned Simmons
---------------------------

You need some bistable hydraulic, mechanical or electrical memory device
that remembers if the pressure should be increasing or decreasing after the
limit sensors stop signaling the limit condition, and operates the valves
accordingly, and that sequence valve could be the trigger that switches it
at the high pressure side.

The proper sequence valve may do it all. See Figure 2 on the page I
pointed to. Connect the IN port to a tee at the cylinder's port; the
OUT port resturns to tank. It'll act like a relief valve when the
pressure reaches the preset, but unlike a normal relief, won't reclose
until the pressure drops to a very low value.

--
Ned Simmons

Ned - I thought this is it.

Then I realised (?) - the full flow of the pump will always be the
minimum flowing through valve - which will defeat the closing action
we are counting on? This device, the "kickdown valve", is for filling
say a hydraulic cylinder, where the flow comes to a definitive stop at
full stroke? It avoid the energy loss of pumping oil past in-effect
an "intermediate-pressure" relief valve.

I suspect that constant flow from the pump would defeat it ??

Good question, but I don't think so, as long as the valve and the
return piping are sized such that the pressure at the OUT port (at
full flow) is low enough that the "light spring" in Fig 2 can force
the spool closed.

In other words: the pressure rises to the set point; the "control
relief poppet" opens, releasing the balancing pressure on the back
side of the main spool; the spool shifts open, and the pressure at the
IN port drops; the control poppet closes, but; the "kickdown jet" is
now open and bleeds the balancing pressure from the back of the spool,
until; delta P across the spool * spool area spring force and the
valve closes.

I hope that's right. Whether this is a practical way to control your
device in the real world is another matter.


I'll try to do sketches.

I have thought of a circuit I believe would act quickly at the set
pressure - giving the set pressure and no more. I ran with the idea
of having "separate reference pressure system" where a small pump,
large accumulator and pressure in it freely set via an adjustable
pressure relief valve dumping back to the reference-system tank. I'll
try to sketch that too.

Rich S

--
Ned Simmons

Hi Ned.

Your real-world experience enables you to answer this question?

You've already raised the point

"... Whether this is a practical way to control your device in the real
world is another matter."

I was thinking of constancy of pressure at which it triggers.
This thing is perfect when sequencing.
For a fatigue test, hydraulic pressure at trigger = peak force.
This is crucial to the test - for the peak force to be known and constant.
Would this device settle down to triggering at a very constant
pressure, do you reckon?
Within reason, so long as it stays constant, what that pressure is is
just fine - plot the "F=PA" force on the "S-N curve / plot" for
comparability of data.

(That's why I designed a parallel small system "reference pressure"
concept - so the peak force / pressure is accurately at, but neither
more or less, than a constant reference pressure)

Rich Smith

I've designed hydraulic systems that included sequence valves, but I
wouldn't want to make a prediction on how repeatable the cracking
pressure might be, especially at high cycle rates relative to the size
of the device. It's also likely to drift with oil temp, though that's
a slow-changing parameter that could be compensated for manually.
Probably best to speak to manufacturers, Eaton/Vickers, for example.

--
Ned Simmons

On Fri, 21 May 2021 14:15:03 -0400, "Jim Wilkins"
wrote:

"Richard Smith" wrote in message ...
Ned Simmons writes:

...
This is crucial to the test - for the peak force to be known and constant.
Would this device settle down to triggering at a very constant
pressure, do you reckon?

-----------------

I don't know about that valve but I do have lots of R&D experience on
difficult projects.

Generally you design and build what you predict (hope) will work, then
measure and correct until you run out of time, money or patience, and
declare it "good enough". The limit is how accurately you can measure.


It's easy to run out of all three quickly fiddling with a new
hydraulic design. They're messy, difficult to change, and often don't
allow easy access to the parameters you'd like to measure when
debugging.

--
Ned Simmons

Ned Simmons writes:

... ....
...
...

I've designed hydraulic systems that included sequence valves, but I
wouldn't want to make a prediction on how repeatable the cracking
pressure might be, especially at high cycle rates relative to the size
of the device. It's also likely to drift with oil temp, though that's
a slow-changing parameter that could be compensated for manually.
Probably best to speak to manufacturers, Eaton/Vickers, for example.

--
Ned Simmons

Ned - that's what I "feared" - it will likely settle down to a stable
pattern, but what that is will drift around in time, with many
variables, including ambient temperature, etc.

Running 24hrs a day for many days, you couldn't keep fine-tuning to
stay on one condition.

I'm seeing why servo-hydraulic with digital logic control on the basis
of pressure transducer(s) is the way things are done.

By the way Ned - "drift" affects welding - not sure how much that is
your thing. "drift" is central to a funny (?) story.

This Company owner knew I wanted to get ahead, so ordered the Foreman
- "Don't let Richard weld - he doesn't know how to". Well, this job
comes in with far thicker plate than anyone has ever met - even the
"old-timers" with 40+ years experience. They couldn't get their welds
to "stick" in those slot-welds. None knew spray-transfer. Co. had
one really good machine, and I flipped it up into spray and was
putting in these slot welds easier than shelling peas. These big
structurals were up on plinths, so I was up there in the middle of the
shop, on top of these things, putting in the welds no-one else could.

No-one came and asked me how I did it.

Reason - they knew I'd say "Don't know. I can't weld. I just pick up
the torch and it seems to work".

The reason they couldn't just copy my setting, or order me go buy
striped paint while they take the torch and continue on that setting
is - conditions drift...
You have to tune and get back to the right condition every few
minutes.
Variables?
Line voltage?
Ambient temperature?
How long since the machine was turned on?
etc.

If you drift downwards, the wire will stub and the weld will
transition to dip transfer. Get too long and it can burn-back to the
torch which will instantly destroy the contactor tip and probably the
shroud. You'll spend a long time rebuilding your torch (N.Am. "gun")
if you don't know how spray works.

So yes, drift...

Again Ned - thanks, appreciated.

"Jim Wilkins" writes:

"Richard Smith" wrote in message ...

"Jim Wilkins" writes:
...
Do you have the equipment or machinist friends to consider custom
machining as part of solutions? ...

Machining, making parts and equipment... My cider-maker / cider
supplier could feature in that... Can see a need to trade favours...

-----------
So not easily, perhaps shortening a bolt but not to the full custom
extent I would otherwise suggest, like the small piston in the
cylinder end cap. Experimenting is difficult when you are limited to
only what you can afford to buy. My shop is what an inventor would
have dreamed of in 1960 though perhaps not today, after 50~60 years of
wear.

How about electronic test equipment? Capturing the brief peak value
from an analog pressure sensor during rapid cycling will be difficult
without a digital storage oscilloscope.

https://www.aliexpress.com/price/200...sor_price.html

Could be more than that...
Device with an eccentric crank?
Simple and presents a huge bearing area to take high forces.

"Jim Wilkins" writes:

"Richard Smith" wrote in message ...
..
Boot off a CD-ROM? Could do?

_____________
Can do easily.

...

There's a mini-computer called a "Raspberry Pi". Designed by group
endeavour of hobbyists. Meant for education. Uses a "merchant"
embedded-chip for eg. washing machines as its processor.
Might look if that offers a way.
Lots of devices been matched to it.

However, note you "PC architecture / QBasic" way.

"Ned Simmons" wrote in message
...

On Fri, 21 May 2021 14:15:03 -0400, "Jim Wilkins"
wrote:

Generally you design and build what you predict (hope) will work, then
measure and correct until you run out of time, money or patience, and
declare it "good enough". The limit is how accurately you can measure.


It's easy to run out of all three quickly fiddling with a new
hydraulic design. They're messy, difficult to change, and often don't
allow easy access to the parameters you'd like to measure when
debugging.

--
Ned Simmons

-------------------

I bought the largest used baking pan Goodwill had, for working on small
engines and hydraulics.

A low-profile drain for a pan or bucket can be made by turning down one end
of a brass push-on tubing connector into a tubular rivet.

"Richard Smith" wrote in message ...

"Jim Wilkins" writes:

"Richard Smith" wrote in message ...
..
Boot off a CD-ROM? Could do?

_____________
Can do easily.

...

There's a mini-computer called a "Raspberry Pi". Designed by group
endeavour of hobbyists. Meant for education. Uses a "merchant"
embedded-chip for eg. washing machines as its processor.
Might look if that offers a way.
Lots of devices been matched to it.

However, note you "PC architecture / QBasic" way.

----------------------------
Sure. The Pi has the advantage that you can buy and plug in an A/D converter
to read the pressure sensor, and a keyboard and display to monitor the test,
no technician bench skills required. I haven't played with one and don't
know the learning curve for it. Are you generally familiar with computer
hardware and software architecture?

As for the eccentric, I considered it because you could vary the piston
stroke, but you'd need a lathe to make it, the pump drive is more than a
friend could whip out in a spare hour. A pump built into the cylinder end
might give the fastest cycle rate because there's no flow restriction. You
could fine tune the peak pressure during operation with a screw that
displaces oil. A cheap used tie-rod cylinder with a scratched bore could be
cut down to be your pressure chamber. Cylinder rebuilders can provide the
tubing in any length.

On my tractor's homebrew bucket loader attachment hydraulics I turned the
head of a bolt round and grooved it for an O ring, so it can screw into or
out of the oil space without leaking. It operates the variable pressure
relief valve I made to replace the fixed relief the control valve came with.
The tractor's front tires turned out to be the weakest link that limited how
high I could set the pressure.

The decision comes down to what you can build or buy. I've spent significant
time and money becoming able to build what I or the customer wanted,
electrical, optical and mechanical. Right now I'm upgrading my sawmill and
its overhead gantry hoist to handle a larger log than it was designed for.

The sawmill is a large horizontal bandsaw made from salvaged motorcycle
wheels. Thursday was lost to the miserable task of prying off the drive
wheel's tubeless tire, scrubbing the corroded bead seating surfaces and
getting it to hold air. The slow air leak reduced the blade's initial 500 lb
tension and let it wander in the 20 inch long cut. I learned manual tire
repair at the Hardway School (an Army motor pool) on split rim truck tires.
As the tire store manager told me, a 2" right angle air sander is the
perfect tool for cleaning up a leaking rim. My tractor's rusted wheels will
be its next victims.

Would fatigue cracking in oil be similar enough to cracking in air, which
oxidizes freshly exposed steel?

On Sat, 22 May 2021 09:01:35 -0400
"Jim Wilkins" wrote:

snip
Would fatigue cracking in oil be similar enough to cracking in air, which
oxidizes freshly exposed steel?

And what about heat? Flexing metal creates heat. If you accelerate
flexing to speed up failure detection you will likely create heat that
would not be present in its actual use...

--
Leon Fisk
Grand Rapids MI

"Leon Fisk" wrote in message ...

On Sat, 22 May 2021 09:01:35 -0400
"Jim Wilkins" wrote:

snip
Would fatigue cracking in oil be similar enough to cracking in air, which
oxidizes freshly exposed steel?

And what about heat? Flexing metal creates heat. If you accelerate
flexing to speed up failure detection you will likely create heat that
would not be present in its actual use...

--
Leon Fisk
Grand Rapids MI

----------------------

That's a good point, however since the sample is in an oil bath its
temperature is easy to control with equipment that can be added later, if
needed.
https://www.wattco.com/product_category/band-heaters/

"Richard Smith" wrote in message ...
....
This Company owner knew I wanted to get ahead, so ordered the Foreman
- "Don't let Richard weld - he doesn't know how to". Well, this job
comes in with far thicker plate than anyone has ever met - even the
"old-timers" with 40+ years experience. They couldn't get their welds
to "stick" in those slot-welds. None knew spray-transfer. Co. had
one really good machine, and I flipped it up into spray and was
putting in these slot welds easier than shelling peas. These big
structurals were up on plinths, so I was up there in the middle of the
shop, on top of these things, putting in the welds no-one else could.
....

--------------------------

You could get a high-paying job welding submarine hulls, and be invited
aboard for the test dive.

"Jim Wilkins" writes:

You could get a high-paying job welding submarine hulls, and be
invited aboard for the test dive.

There is a submarine base nearby.
Very exacting recruitment.