"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