Pilot Relief Valve..Simple Question!!

Simple answer, then:

When the line is disconnected, the valve shuts, and no longer "farts" into the relief line. The valve not opening to relieve the pressure might have consequences:

• If the line is to remain disconnected, there is a burst disc on the tank, isn't there? Isn't there?

the pilot line is connected with a hand valve and then with the tank..so we can disconnect and connect the extra tank..so..because i dont really understand the answer..the answer of my problem is that the extra tank of the pilot line when is not connected shut the valve and cannot relieve. when is connected give relieve to the relief valve and the relief valve is working correct?

I have looked at the schematic and noticed a couple of things. This three position control valve dumps to tank and all ports are connected when in the center position. With the pump running look at the pressure gauge---(it may read 0 pressure) (But if the pump can oversupply the lines capacity to drain the oil to tank it may read pressure) if it reads any pressure the load cylinder could creep ahead because of the difference in the area from the shaft side of the piston to the top side of the piston. A valve with A and B ports(cylinder ports) blocked and pressure connected to tank in this position is much safer if the pump can oversupply the lines capacity to drain the oil to tank. If you move the valve to lift the load (flow lines crossed) the load will lift but the gauge could still read 0 because oil is going back to tank on that line where you got the gauge. If you lower the load (the flow lines parallel on the valve) the gauge reads full pressure because of where the gauge is on the line. Your system is prone to noise when the load is not being moved. If you leave the control valve in either the move forward or retract position the relief valve will dump after the cylinder reaches full stroke. The hand operated valve from the pressure relief valve from the drawing should be shut and the system should still work. Unless the second tank you are vaque about that is connected to the hand valve is actually an accumulator in which cause the hand valve is open to smooth and cushion pressure. (An accumulator is a sealed tank with a gas bladder to maintain pressure)

Hope this clears up the fog

Robert

Relief valves keep a hydraulic system from overpressure. Is it possible that the pilot line is controling the maximun pressure and is keeping the relief valve shut but it is now poping open and close (making noise) because the system pressure is too high or because there is a leak in the pilot line? When you remove the pilot line the system loses pressure because the pilot is no longer keeping the valve shut to maintain pressure. This is only one possiblity. Because hydraulic systems with sticking valves can act in unexpected ways you should have a professional look at it if you are not sure. There are any number of ways a hydraulic system can be made and dozens of types of valves. If you have a schematic drawing or picture of the valve setup I may be able to help. I have many years experience and you could do damage and get hurt if you don't hook things up properly.

Robert

First of all I wonder why there are two tanks. When the pilot line is disconnected from the tank by a valve you mention that there is pressure drop? or pressure reduces? and then the noise stops. What kind our noise - is it hammering noise or noise of fluid passing. A circuit would be helpful in understanding. What are the pressures max, min

I normally try to NOT write overly aggressive posts about 'stupidity' but this may be the exception.

Of course it makes a noise and stops ...

An overpressure valve operates against against ambient. If one is 'stupid enough' to think "Oh I'll just connect that 'blow-off' to a capture vessel, the pressure in vessel 'A' will rise, as the 'blow off' thinks the back pressure from vessel 'B' is 'ambient', until vessel A explodes.

ARrrrrrrrrrrrrrrrrrrrrrrrrrrrhhhhhhhhhhhhhhhhhhh!

George; the way to do this is via a separate line, with a regulator set below 'blow-off' operating a pilot operated bleed valve, feeding vessel 'B'.

God, please tell me this is "homework"

yeah..is like a small homework..we have to understand why is this happened..:) but i m not understand yet..when the pilot line is disconnect the pressure is 0.8 bar..when is connected is 80 bar(max)..when the cylinder is retracted and the lever continues to try to retract the cylinder is making noise like flow passes..

When pressure drops to 0.8 bar - it means when you actuate (open) the shut off valve, the pilot line drains to tank and then main relief valve opens to tank. The opposite action of the shut of valve closes the pilot line to the tank and therefore allows the main pressure relief valve piston to seat under pressure. When you continue to retract the cylinder the cylinder cannot move further and the oil blows over the relief valve at high pressure at 80 bar making the noise (when flow passes over the relief valve)

thnx very very much..!!! but i think that in my case is the opposite..when the hand valve is open the pressure is 80 bar..when is close is 0.8..

Ok, now I'm fully confused. Maybe it's the terms

Is "tank" a storage vessel? or accumulator? A thing that just holds oil or air?

or is "tank" a cylinder or ram or actuator? Has a piston that moves?

Is this "pilot operated relief valve" an over pressure relief valve? Oil goes to a reservoir, or sump, for re-pumping?

Or is it a 'pilot operated non return valve'? Fits between cylinder and supply hose, to allow, or not allow, flow?

Do you have a circuit diagram - can you post a photo of the diagram, or the components?

http://img132.imageshack.us/img132/6987/35189372.png

Registration required - nup, I have enough spam. Post her via the camera icon

Does your hand valve have a wheel on it, or is it a lever type ball valve?

is a hand valve with lever..just to close and open the pilot line..to see the difference..

O.K. remove the valve and look through it to see that 'open' is actually open.

From your description it sounds like you have connected the pilot line to the relief valve in such a way that the pressure holds the relief valve shut.

However this will blow up whilst configured this way.

The diagram shows a spring in your relief valve. This spring should be all that is required. It should be set at the relief pressure.

You say that when you open the relief valve pilot line ( via a hand valve ) the pressure drops to 0. This would indicate that the relief valve is connected incorrectly. The spring should hold it shut until it reaches the predetermined pressure.

I suspect the only way the hand valve/pilot section should be used is to overide the spring to OPEN the relief valve to dump pressure in an emergency. You seem to be using it to overide the spring to clamp the relief valve SHUT untill the system blows up. This would create a lot of noise along the way.

Dear referring to the circuit you have provided, the explanation i have given earlier is correct. Now the point is why this valve is provided. This valve could be provided far away from the main system or relief valve (on the control panel) to provide you easy access to help you to dump the oil to tank on regular basis or during emergencies. Now since the pressure is 80 bar which is not a very high pressure, what is your problem. Is noise your problem? then you cannot help it. Is oil heating your problem ? then the arrangement of opening the valve to dump the oil to tank is fine instead of allowing the oil to pass thru the direction control valve. So actually there is not problem to this situation.! If you still have queries I will be happy to clarify.

thnx for ur help..:)))

Thanks for the diagram George.

Sorry for not responding sooner - I was elsewhere.

As shown the control valve is shut. If the pump is running oil will go through the relief valve. This usually makes noise. As it will, when the cylinder reaches full stroke in either direction.

One could install a pressure switch in the pump outlet line to turn off the pump.

But if this is a frequent 'restarting' cycle, it means a lot of pump off and on.

I would recommend you use a control valve with integral flow diversion - such as used in bulldozer hydraulics for blade, rippers etc.

The diagram for that is like yours, except the center position has a 'U' directing flow straight from pump-in to reservoir-out, and both cylinder lines are shut [so the cylinder is 'locked'].

It's also possible you have that valve - but it is connected back to front.

If so you will be able to move the cylinder [by force] when the valve is in neutral.

Hoses do not always connect like diagrams. So you MUST identify the ports.

Take a careful look at all the port markings of all components. As they may be in English - and I'm guessing you are not - you need to check what each letter or number means at the makers website.

If unsure, take pictures of your stuff, showing maker and numbers, and post them here.

Well picked on the control valve. ( i've given a GA ) I didn't pay cognisance to the center position as shown. I assumed that it would be one side or the other not able to be in the center position.

I know I know, never assume anything.

cheers

Jim

When you continue to retract the cylinder the cylinder cannot move further and the oil blows over the relief valve.

Looking at the circuit diagram i see the pressure from the return side of the ram going straight to the tank NOT through the relief valve. However i believe you are right in saying

The opposite action of the shut of valve closes the pilot line to the tank and therefore allows the main pressure relief valve piston to seat under pressure.

I will go further and say that the pilot is, incorrectly, holding the relief valve either open or shut.

Jim

thnx very very much!!!! ur comments was very helpfull!!! thnx a lot!