Relief Valve in Cylinder Circuit with Counterbalance Valve

[shtevie]

Hi there,

I'm looking for some advice on a circuit.
In the attached schematic, could anyone foresee any issues with setting the counterbalance valve (CB1) to 210 bar, and removing relief valve RV2?

Settings:
RV1 = 190 bar
RV2 = 210 bar
RV3 = 90 bar
CB1 = 250 bar

Thanks

 

[kiwitom235]

i can see other issues than just that.

How will you raise the cylinder? If the working pressure required is 210 Bar, you will relieve through RV3 (90Bar), so the cylinder wont move.

You seem to have to many relief valves, Why dont you just use one R.V. and one C.B.

Also, you should use an open centre directional valve.

 

[HPost]

I suspect that the 210 BAR relief valve (RV2) is there to protect the cylinder from static loading.

If a load is placed on the cylinder that causes the pressure to rise above 210 BAR, what will protect the cylinder? It could be that the cylinder will buckle above 210 BAR.

The directional valve is open centre, it has 6 ports and 3 positions.

The 190 BAR relief valve (RV1) will limit the dynamic pressure, the pressure at the pump.

RV3 sets the maximum lift pressure.

The cylinder will lower at approx 166 BAR.

You need to verify the cylinder buckling calcs before you remove RV2.

 

[kiwitom235]

HPost, The counterbalance valve will protect the cylinder from static loading will it not? It is also a relief valve after all...

The control valve is not open centre, look at it, it has 4 ports blocked in middle position!

Why dont you just use a simple circuit like htose here:

http://www.comatrol.com/application-notes

 

[HPost]

I have looked at it. In the neutral position, the pump is connected to tank.

The counter balance valve is set to 250 BAR and will open at 166 BAR if there is a pilot signal from the rod side of the cylinder to push the valve open.

With no pilot signal, the counter balance valve is just a relief valve set to 250 BAR.

 

[hydtools]

If the counterbalance valve is used as a relief valve when the directional valve is centered, the counterbalance relief flow would have to pass through RV3. The pressure at the cylinder would then be 210 + 90, if RV2 is eliminated and the counterbalance set to 210.

HPost is correct in that the pump is connected to tank when the directional valve is centered.

Ted

 

[kiwitom235]

seems like an over-complicated circuit to me. more RVs than what is actually required to achieve the same result.

With the working load applied the pilot pressure will need to be 26.7Bar to lower the cylinder. But it doesn't matter anyway as RV2 will open at the working pressure.

why not just use a simple circuit like this (

http://valveproducts.net/upload/images/counterbalance-valve/press-circuit-b.jpg)

with perhaps an additional RV after the pump.