pressure drop in relief valve (prince RV-1H)

[orangetree]

None of the "datasheets" for relief valves I can find seem to provide a flow-vs-pressure-drop curve. I'd like to know so I can verify the heat load & pressure loss I'm incurring here is acceptable.

---

I'm modifying my hydraulic system to function with a grapple as if it were built into my FEL valve (and that valve was series plumbed). This means it's upstream of the FEL valve - and thus upstream of the factory pressure relief.

My system is ~7gpm, 2631psi. What's the pressure drop across a pressure-relief valve at 7gpm?

Note I penciled in Prince RV-1H for the following reasons:

• seems like a highly reliable brand / part. Any other valve can fail on my system, and it's just downtime to replace that valve, for some I could even continue using other functions if what i'm doing isn't blocked. BUT not so for the main pressure relief valve - if that fails, I run the risk of blowing up the pump or possibly other stuff. So for this part I'm more quality sensitive than I might other wise be.
• Rated for flow well above mine (30gpm), I hope/assume this means minimal pressure drop

 

[orangetree]

For the curious, the modified system will flow

1. pump
2. --> (new) pressure relief
   1. obviously has it's own return to tank
3. --> (new) valve, tandem center; size D05 for minimal pressure losses P->T**
   1. **T is fully pressurized here.
      1. There is no return to tank on this valve/manifold.
      2. So the system functions at full flow as long as the grapple cylinder can move freely.
      3. Which is what i want - I'm open-center, i only want expect to have this "series" functionality during "repositioning" / un-loaded operation
   2. Cylinder exhaust port flows directly to FEL valve when fully open; when partially open, (flow split A->B & P->T), all flow downstream still goes to FEL valve.
4. --> existing FEL valve (including pressure relief, rear remotes, etc)

as covered in some other recent threads.

 

[oldnslo]

I presume you asking about flowing the relief body not through the relief to tank. Depending on relief valve style Some bodies have a hole straight through and others have the relief cartridge with passage around the cartridge. In either case I would suspect minimal drop through the body unless ports are way undersized for flow rate.

 

[orangetree]

I presume you asking about flowing the relief body not through the relief to tank. Depending on relief valve style Some bodies have a hole straight through and others have the relief cartridge with passage around the cartridge. In either case I would suspect minimal drop through the body unless ports are way undersized for flow rate.

Correct - i hope that pressure drop line to tank would be 100% of my system pressure

The "cartridge" aspect was actually what prompted this question. The RV series is a cartridge BUT goes up to 3000psi. The smaller RD series (RD-1800) is a "direct acting" ball (cuttaway seems to show literally a straight channel + relief ball out of the way: i recon this is zero pressure drop...) but only goes to 2500psi

Further, the RD is advertised as "fast opening" - do i care about this? / should i be looking for another mfg with a higher pressure "direct acting" ball?

I've attached the only "datasheet" i can find here

 

[oldnslo]

Fast acting would help clip pressure spikes but not certain if you would notice on your application. Typically differential area has lower pressure rise that ball type direct acting. Looking at those curves the ball type was terrible for rise vs flow during operation.

 

[orangetree]

Fast acting would help clip pressure spikes but not certain if you would notice on your application.

AFAICT, it's only safety / longevity of pump that I'm "worried" about regarding actual performance of the device, not so much how much a human operator would notice anything. I'm not really sure what there is to "notice" in relief valve operation, anyway - a larger audio "pop" at the beginning of it opening iff it's "too slow" and dangerous pressure spikes build? Note there is very little elasticity in the system here - stock setup has metal pipe (pump)-->(FEL); thus this new valve will be essentially the same (just a short hose coupler/adapter for (pump)-->(new Relief valve)

Typically differential area has lower pressure rise that ball type direct acting. Looking at those curves the ball type was terrible for rise vs flow during operation.

I could easily be wrong - but the way I interpreted those curves is pressure drop when activated / OPEN - eg (pump)-->(atmospheric tank). The spring/ball valve has a steeper rise in pressure there as flow increases, which might make sense as it's the full flow pushing against the full ball to keep it open. Contrast to the cartrige type which can use some sort of "pilot" operation or similar, requires less effort to keep the valve open [once triggered]

not the pressure drop the across the valve when closed.

 

[oldnslo]

Yes rise when activated is what I called pressure rise. This is semi important to consider when designing a circuit. Example with RD1800 rise was over 200 PSI from 1 to 8 GPM this means you start losing flow at 200 PSI below system setting. This can reduce lifting capabilities especially when tractor is idled down.

Fast response vs directing acting ball vs system life. Not sure how to answer that question. I would guess that 95+ % of circuits have standard response relief valves. Where I have seen fast response is on systems where there was potential for high spikes. I could be 100% wrong but I doubt your circuit would have component threatening spikes with standard response relief valve.

 

[orangetree]

Example with RD1800 rise was over 200 PSI from 1 to 8 GPM this means you start losing flow at 200 PSI below system setting.

Good question - am i understanding this wrong?

Call the three ports on a pressure relief valve Pin, Pout, and T(ank).

I see the high head across the relief valves "when they are relieving" eg open Pin-->Tank

But my understanding is I would adjust that valve such that my actual system pressure when it opens is as desired (2631 psi). THEN, yes, the valve has a ~200psi head across Pin-->Tank (and the full 2631psi across Pin-->Pout, as we're talking about max relief flow - some cylinder is dead-headed with the valve still open)

But that doesn't mean I can't have cracking pressure at full 2631 psi ... just that when the over-pressure is operating (eg, i have the FEL deadheaded but am stubbornly pulling that lever ... hearing the "whine" of the OPvalve) - it's making a decent amount of heat. So if i leave it there, i might heat up the fluid.

Or is that 200psi somehow relevant to Pin-->Pout?

 

[orangetree]

talked to a Prince FE; they're going to get back to me on the actual pressure across (Pin --> Pout),

but they did note that the RV line ("differential poppet inline relief") is the exact same cartridge style that is used in Prince FEL valves. So that adds a fair amount of confidence as that's apples-to-apples with my application.

They also noted that a direct acting, ball/spring type relief valve might NOT be appropriate for this use case as well; Because of the simple action, pressure spikes from the pump (recall the system is pretty inelastic between the pump and the system OP valve - all steel pipe), the ball might actually see repeated small actuation, causing wear and eventual constant leakage.

 

[oldnslo]

Orange
You cannot have cracking pressure and full system pressure be the same on RD valve. In my example above the valve would crack at approx 200 PSI lower than full flow set point.

Yes ball type relief can have some instability which will potentially cause premature failure.