Direct acting or piloted relief valve ?????

[xtal01]

I went to order the valves for my project and the person taking the order said I should change the valve I picked out for my relief valve.

I picked out a direct acting valve since it had a very low leak rate ... 5 drops per min.

He suggested a piloted relief valve because it was "quieter".

Is he right?

I didn't think the relief valve should ever be used so I may want it louder to alert me if it is being used .... or is it "really" loud? On the original forklift, I am sure the relief valve actuated every time I hit full stroke and I don't remember it being that loud.

Looking at my circuit, maybe a small leakage would not matter though?

Looking at my circuit, maybe I even have it in the wrong spot ... should it have been before the pump check valve? It would then protect the pump 100% but not the entire circuit?

Any advice ?????

Again, circuit diagram attached.

Thanks .... Mike

 

[HPost]

Yes pilot operated relief valves can be quieter than direct operated, but they are more expensive and prone to contamination. They also have a leakage value, as you point out.

All that said, a well designed direct acting valve should not be noisy.

Try the direct operated valve first, if it's too noisy, change it.

 

[xtal01]

Do you recommend putting it before or after the pump check valve?

If the valve is protecting just the pump, then it makes sense to put it right after the pump ... which also makes sense because in my mind it should have nothing between the pump and what is protecting it.

On the other hand, if I ever think there could be anything that would cause an overload in the system ( I don't known what ... I can't imagine a sudden load of over 3000 lbs on the lift since the second floor would not even take that weight ... but one thing I have learned is to never say never ), then I think were it is now is the right spot.

Thoughts???

Thanks again .... Mike

 

[HPost]

The only reason to install it at the pump would be if you think that the check valve could fail closed at some point.

Things can and do go wrong, it's your choice to decide how to mitigate the risk.

If it is necessary, add another valve to protect the pump, just make sure that it set higher than the "system" relief by at least 20 BAR, otherwise they can start to affect each other.

 

[hydtools]

A direct acting relief valve may squeal or chatter more, but then you know it is working. It will also have a greater difference between full flow pressure and reseat pressure and between cracking pressure and full flow pressure. I don't believe the difference between the relief valve type performance will make any difference in you system.
Either valve would be downstream of the pump check valve to provide over-pressure protection for all system components.

Ted

 

[kiwitom235]

direct acting relief valve should be fine. Also, direct acting relief valves will better at relieving any rapid pressure spikes that may occur in the system, although i don't think this would be an issue for you. pilot operated relief valves often cant open fast enough to sudden pressure spikes.

A funny example of this with my old work, my boss had a customer who was having trouble with seals blowing on cartridge valves in their system they had designed. They had a pilot operated relief. They were blaming our products. My boss said it could be pressure spikes that are to quick to be picked up on the pressure gauge, and that the pilot operated relief cant react to. They didn't believe it, so he bet them that if they switched the pilot operated relief for a direct acting relief the problem would be sorted. he said if it didn't work we would give them all the products we had sold for their system for free, and if it worked they only had to pay for the new relief valve. they put a bucket under the relief port, and lo and behold after a day or so there were a few drops of oil in the bucket, showing that every now and then there was a huge pressure spike which would squirt a bit of oil out of the direct acting relief.

Sorry about the long post, just thought it was a good example to share!

Cheers,

Tom

 

[xtal01]

You guys are the greatest!

The amount of information you have given me is awesome. I have learned more in the last month about hydraulics than I ever could have gathered anywhere else. A description in a text book is no substitute for real world knowledge.

Mike