I am learning about hydraulics presently and am fascinated by their
simplicity and potential. There are a number of issues that are still
unclear to me and I would be appreciative if someone could answer these
questions if I post them here from time to time...

The first being with regards to the hydraulic pump. It appears that 2200 PSI
is a standard line pressure used in hydraulics, do all pumps produce this
pressure with the variation between pumps being the flowrate or are all
pumps basically the same with the flow rate and pressure being determined by
the power source for the pump ?

For example does a pump produce either high pressure at a low flow rate or
low pressure at a high flow rate with the flow rate and pressure determined
by the power source ?

I understand that

Thanks

Murphy

Murphy wrote:
I am learning about hydraulics presently and am fascinated by their
simplicity and potential. There are a number of issues that are still
unclear to me and I would be appreciative if someone could answer these
questions if I post them here from time to time...

The first being with regards to the hydraulic pump. It appears that 2200 PSI
is a standard line pressure used in hydraulics, do all pumps produce this
pressure with the variation between pumps being the flowrate or are all
pumps basically the same with the flow rate and pressure being determined by
the power source for the pump ?

There isn't a standard pump design; you get thousands of different pump
designs with different working pressures and displacements. Also note
that the pressure quoted is the maximum working pressure. If you
connected a pressure gauge to the system it wouldn't necessarily show
this pressure. The actual pressure depends on the load on the system.

For example does a pump produce either high pressure at a low flow rate or
low pressure at a high flow rate with the flow rate and pressure determined
by the power source ?

You do get variable displacement pumps (i.e., you can change the volume
of oil discharged per revolution of the shaft), but these are less
common than fixed displacement pumps.

Hope this helps,

Chris

On Sun, 31 Jul 2005 11:06:49 +1000, the opaque "Murphy"
clearly wrote:

I am learning about hydraulics presently and am fascinated by their
simplicity and potential. There are a number of issues that are still
unclear to me and I would be appreciative if someone could answer these
questions if I post them here from time to time...

Get thee to the library and read up! Or grab inexpensive books off
www.Half.com , www.Ebay.com , etc.

Audel put out some, like "Pumps, Hydraulics, & Air Compressors",
"Pneumatics & Hydraulics", etc. Audel books are all KEEPERS! I have
half a dozen of them now covering quite a range of subjects. (They'll
be better than gold after "the fall." /survivalism)

I've found others on Ebay like "Let's Get Into HYDRAULICS, Farm
Equipment ELECTRICAL SYSTEMS, Hydraulic Systems DIAGNOSIS", a
collection of articles from Implement & Tractor Magazine. It covers
both theory and troubleshooting.


The first being with regards to the hydraulic pump. It appears that 2200 PSI
is a standard line pressure used in hydraulics, do all pumps produce this
pressure with the variation between pumps being the flowrate or are all
pumps basically the same with the flow rate and pressure being determined by
the power source for the pump ?

Pumps of a given displacement are designed for a certain flow and
pressure. Variable-displacement pumps are one exception. Valving
can alter flow, too, as can regulation.


For example does a pump produce either high pressure at a low flow rate or
low pressure at a high flow rate with the flow rate and pressure determined
by the power source ?

I'm fascinated by it, too. From what I've read, flow is pretty much
set by the pump volume @ RPM and pressure is adjustable within a given
range as determined by the type of regulator.


--
Guns don't kill people. Rappers do!
-----------------------------------
www.diversify.com Rap-free Website Development

On Sun, 31 Jul 2005 11:06:49 +1000, "Murphy"
wrote:

I am learning about hydraulics presently and am fascinated by their
simplicity and potential. There are a number of issues that are still
unclear to me and I would be appreciative if someone could answer these
questions if I post them here from time to time...

The first being with regards to the hydraulic pump. It appears that 2200 PSI
is a standard line pressure used in hydraulics, do all pumps produce this
pressure with the variation between pumps being the flowrate or are all
pumps basically the same with the flow rate and pressure being determined by
the power source for the pump ?

For example does a pump produce either high pressure at a low flow rate or
low pressure at a high flow rate with the flow rate and pressure determined
by the power source ?

I understand that

Simple overview:

Pumps deliver a flow rate determined by displacement and RPM.
Pressure is determined by the load and other factors, though the pump
and drive will have a maximum pressure rating.

Hydraulic pumps are "positive displacement" pumps that move a
certain volume of liquid per revolution, nearly regardless of
pressure.

If there is nothing to resist flow then pressure will be very low.
If there is resistance, as perhaps a cylinder with a load, then
pressure will increase until one of the following happens:

* the load moves when hydraulic force exceeds load resistance
* the motor stalls or a clutch or belt slips
* something breaks
* a pressure-actuated relief valve diverts flow around the load

Liquid flow rate is determined by the displacement of the pump and the
speed at which it's driven. Operating pressure is determined by the
load: light load = low pressure. Max pressure is determined by
the ratings of the pump, the hydraulic lines, and whether the drive
(motor, belts, etc) can deliver the torque to produce that pressure.
Pressure is often limited by a bypass valve that will divert flow at
some set pressure, like the 2200 PSI you mention. This valve may be
incorporated in the pump rather than being an external entity.

"Murphy" wrote in message
...
I am learning about hydraulics presently and am fascinated by their
simplicity and potential. There are a number of issues that are still
unclear to me and I would be appreciative if someone could answer these
questions if I post them here from time to time...

The first being with regards to the hydraulic pump. It appears that 2200
PSI is a standard line pressure used in hydraulics, do all pumps produce
this pressure with the variation between pumps being the flowrate or are
all pumps basically the same with the flow rate and pressure being
determined by the power source for the pump ?

For example does a pump produce either high pressure at a low flow rate or
low pressure at a high flow rate with the flow rate and pressure
determined by the power source ?

I understand that

One off the basic concepts to understand is, pumps only create flow. The
pressure is caused by resistance to that flow (ie the load).

In article ,
"Murphy" wrote:

I am learning about hydraulics presently and am fascinated by their
simplicity and potential. There are a number of issues that are still
unclear to me and I would be appreciative if someone could answer these
questions if I post them here from time to time...

The first being with regards to the hydraulic pump. It appears that 2200 PSI
is a standard line pressure used in hydraulics, do all pumps produce this
pressure with the variation between pumps being the flowrate or are all
pumps basically the same with the flow rate and pressure being determined by
the power source for the pump ?

For example does a pump produce either high pressure at a low flow rate or
low pressure at a high flow rate with the flow rate and pressure determined
by the power source ?

I understand that

Thanks

Murphy

Pumps will be sized by displacement. Usually cubic inches of oil
pumped per revolution of the pump. The flow rate will be determined by
how fast you spin the pump. Revolutions per minute times displacement
is cubic inches per minute. Divided by 281 (IIRC) gets you gallons per
minute oil flow. In the case of variable displacement pumps it will
list the maximum possible displacement.
Pumps have a maximum operating pressure, typically 3,000 PSI for
hydraulic equipment. A relief valve somewhere downstream from the pump
will be set lower than that most of the time. That's where that 2,200
PSI number comes from.
Your actual pressure when working depends on how much is required by
the load on the system. If you actually need 2,000 PSI to move it, the
pump will deliver 2,000 PSI as long as it is turning. OTOH, if the load
only needs 50 the pump will only deliver 50.
The relief valve sets an upper limit that system pressure can reach.
That keeps you from killing the engine, blowing off lines, or damaging
the pump. If your load needs more pressure than your relief allows, you
can't move it.
In systems with variable displacement pumps there is often a small
servo attached to the pump that will cause displacement to go down as
pressure goes up. That way the horsepower used remains constant and
heavier loads will just move more slowly without bogging down the
engine. Those systems can have a much higher maximum pressure and
usually don't use a relief valve. The pump displacement will just be
turned to zero before anything breaks.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/

231 cubic inches per gallon

B.B. wrote:
In article ,
"Murphy" wrote:


I am learning about hydraulics presently and am fascinated by their
simplicity and potential. There are a number of issues that are still
unclear to me and I would be appreciative if someone could answer these
questions if I post them here from time to time...

The first being with regards to the hydraulic pump. It appears that 2200 PSI
is a standard line pressure used in hydraulics, do all pumps produce this
pressure with the variation between pumps being the flowrate or are all
pumps basically the same with the flow rate and pressure being determined by
the power source for the pump ?

For example does a pump produce either high pressure at a low flow rate or
low pressure at a high flow rate with the flow rate and pressure determined
by the power source ?

I understand that

Thanks

Murphy


Pumps will be sized by displacement. Usually cubic inches of oil
pumped per revolution of the pump. The flow rate will be determined by
how fast you spin the pump. Revolutions per minute times displacement
is cubic inches per minute. Divided by 281 (IIRC) gets you gallons per
minute oil flow. In the case of variable displacement pumps it will
list the maximum possible displacement.
Pumps have a maximum operating pressure, typically 3,000 PSI for
hydraulic equipment. A relief valve somewhere downstream from the pump
will be set lower than that most of the time. That's where that 2,200
PSI number comes from.
Your actual pressure when working depends on how much is required by
the load on the system. If you actually need 2,000 PSI to move it, the
pump will deliver 2,000 PSI as long as it is turning. OTOH, if the load
only needs 50 the pump will only deliver 50.
The relief valve sets an upper limit that system pressure can reach.
That keeps you from killing the engine, blowing off lines, or damaging
the pump. If your load needs more pressure than your relief allows, you
can't move it.
In systems with variable displacement pumps there is often a small
servo attached to the pump that will cause displacement to go down as
pressure goes up. That way the horsepower used remains constant and
heavier loads will just move more slowly without bogging down the
engine. Those systems can have a much higher maximum pressure and
usually don't use a relief valve. The pump displacement will just be
turned to zero before anything breaks.