Second stage pressure for piloted relief valve.

[Kostet]

Hi, I'll appreciate any advice on this.

Let the spring 9 cracking pressure setting be 400bar. Main line pressure P is 300bar. What pressure do we need to supply via pilot port X to overcome spring 9 setting - 110bar or 410bar?
Thanks.

 

[HPost]

If pressure in the X port is the same as the pressure in P port, then P port pressure will be 400 BAR. If you back spring (9) off to 300 BAR, the pressure in the P port will be 300 BAR.

In other words, the valve responds to the pressure in the X port, not the P port. It doesn't matter what pressure is in the P port is the X and P port are separate.

If you want pressure in the P port to be 300 BAR max, then you have to set the pressure of spring (9) to 300 BAR. The X port also needs to be connected to the P port.

If you want remote pressure setting, that is fine, but you will get a different pressure in the P port.

What exactly are you trying to achieve?

 

[Kostet]

Hi, thanks for the reply. I'm trying to understand how the valve works with different pilot pressures. The description says ports P and X are connected via orifice 4 (not separate).
Also it is said that the valve can be unloaded or changed over to another pressure via port X.
Imagine the situation: spring 9 is set to 400bar cracking pressure, P pressure is 300bar, port X blocked - so, spool 3 is closed.
What happens to the valve if we supply 450bar pressure via port X?

 

[HPost]

OK, I see

Hopefully you can see that the valve functions by controlling the pressure on both sides of the main poppet. Using internal orifices, when the pilot section opens and the pressure differential across the main poppet is enough to open the valve, oil flows from P to T, whilst the set pressure is maintained.

If you block the X port and use the internal pilot, the valve will remain closed until you exceed the force at spring (9). The pressure to exceed the spring force comes from the P port, so that must also be above the spring valve. Spring (9) value is 400 BAR, so pressure in P port will be 400 (plus a little for the pressure drop over the control orifices 4 and 11).

If you add a signal to via the X port, the valve will still open at 400. Even if the signal in X is 450 BAR. Why do want 450 in X and 300 BAR is P?

 

[Kostet]

Yes, this is clear for me, thank you. But I still can not get what do they mean by saying in the last sentence of description - the pressure relief valve can be changed over to another pressure (second pressure stage) via port X.

 

[HPost]

It means that you can have multiple pilot stages with different pressure settings.

You would set the max pressure on the pilot stage mounted to the main valve(as shown above). Let's say that is set to 400 BAR.

You can then connect another pilot section via the X port. This would be set to a lower pressure, say 350 BAR, but isolated by a solenoid valve or a hand valve. So if you want P to be limited 400 BAR, you isolate the remote valve. If you want 350 BAR in P, then you would open the isolation valve and the pressure in the X port would be limited to 350 BAR. It's a method of having different pressure settings without having to adjust the valve every time.

It is possible to have multiple remote pilot stages, but the pressure settings must be carefully spaced so that they don't overlap and they cannot be too far away from the main valve otherwise the response time of the valve can be a bit slow, allowing the pressure in P to go higher than the required value.

 

[Kostet]

OK, thanks a lot. This is exactly what I'm going to do - installing pressure regulator below X port for lowering pressure at P (what they call unloading). I think I was confused by the valve pic and two triangles at port X - white and black. I thought black one represents some excessive supplied pressure, say 410-420 bar which cracks spring 9 (set to 400 bar) and allows flow from P to T even if P was lower than 400bar.
Now I see it does not work like this. Thanks again.