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Maybe I'm missing something, but if your fixed displacement pump is putting out 10 GPM, 5 of which is being used at full pressure, 5 at reduced pressure - correct me if I'm wrong, but doesn't the pump see full pressure and flow anyway? Is there any advantage to a pressure reducing valve?

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If you have multiple pressure requirements, you can use a PRV to save (at the very least) a lot of money by being able to use lower pressure rated components in the {same} hydraulic system.

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The whole purpose of a pressure reducing valve is to cause a pressure drop, and thus there will be wasted energy.

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Originally posted by Bud T:
Redpoint wrote;

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If you have multiple pressure requirements, you can use a PRV to save (at the very least) a lot of money by being able to use lower pressure rated components in the {same} hydraulic system.

Redpoint, what happens when the UNTRAINED, and that is the norm for Hydraulics, Turns tha Adjusting Screw on that "SILVER THINGIE" and got his stuck cylinder to move because the pressure increased? However, do you in your wildest dreams believe that Untrained person will go back nd readjust the Reducing Valve back to its original setting even if he bothered to check it before screwing the adjustment in???????

Then who is at fault when a cheaper Hose or Valve, allowed by the reduced pressure in that circuit, Blows Up and INJURES SOME INNOCENT BYSTANDER OR OTHEF UNLUCKY SOUL????? Who gets to pay for Loss of Life or a Debilitating Injury??? I don't think most Fluid Power Designers will use a Reducing Valve to cut the cost of components 15% and take te chance that the pressure will remain at a safe level for the CHEAPER COMPONENTS.

Just a thought.

I don't believe Rory Mclaren would think very highly of the above scenario either.

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I was giving an example of how a PRV "may" be used and maybe that wasn't the best example. You would normally protect that part of the system with a pressure relief valve. That being said, one could argue that a pressure relief in ANY system could be improperly adjusted with accident potential.

Usually a when pressure relief valve is adjusted higher than the initial setting it causes Electric Motors to OverHeat at best or downright stalls them in most cases. I can't say adjusting a Relief Valve higher than design pressure never happens just that it usually causes problems immeiately. The other point is, even untrained persons know what a Relief Valve is and rarely adjust them to a higher pressure without getting input from the circuit designer.

"Also, by lower rated components I didn't mean "cheaper".

In my thinking that would be the only reason for applying lower rated components.

"Now, if I was quoting a hydraulic system that used multiple pressures. (ie. multiple cylinders w/multiple pressures) I would probably quote the system BOTH ways, all high pressure cylinders AND/OR some heavy duty, some medium duty and let the customer decide."

That will work but can come back to haunt you when one of the lower rated components fails. Never seemed worth it to me. I never made any commission on service calls for machines that failed due to using lower rated components and I never made points for those service clls either. However, I got a lot of repeat business from satisfied customers and a lot of leads from them also when a service call was from lower rated components that needed replaced.

"Are you telling me you've NEVER seen a hydraulic circuit with various pressure rated components?"

I have seen many circuits with the lower rated components and what I saw often made me even more determined to never go that route.

There was one exception to that rule though. When a customer was making a circuit that would be for short run product and then scrapped out lower rated components might be used.

"And I'm not saying it's the best idea either."