Improve response of A11 LS pump

[Jacc]

Hello
I have a crane with large cylinders (rod side volume 160 L or 42 gallons), running A11 260 pumps with LS. What I've noticed is that the response when lowering the boom is slightly slower (a few tenth of a second) than when raising the boom.

Here is what I think:
When raising the boom there is a limited amount of oil between the valve and the CB valves on the cylinders that needs to be pressurized before the boom will lift.
However, when lowering there is a large volume on the rod side (assuming the cylinder is halfway retracted or so) that also needs to be compressed before movement starts.

I believe the initial pressure buildup of the pump is critical, once the pressure is up to 50 or 100 bar it will respond much faster than it will at 25 bar (which is the standby pressure).


So based on this I'm considering putting a 50 or 100 bar sequence valve close to the directional valve's B-port (rod side). That would give the pump instant resistance and pressure would build much faster. The extra heat generated is not an issue at all here.

Any inputs? I know I've left out a ton of details but the key question is really if the difference in non pressurized volume makes a difference in the response of an LS pump. And yes, response is an issue here.

 

[MikeHalloran]

I think you need more liability insurance.

Mike Halloran
Pembroke Pines, FL, USA

 

[HPost]

The bulk modulus of the oil is much higher than the pressures you have, so oil volume will not be the issue with regards to pressure generation.

The most likely reason is the counter balance valve. Going up, the oil goes around the main stage via a check valve. When you lower, you have to generate enough pressure to force the valve open.

You mention the rod end volume, what is the head end volume? Have you accounted for the volume ratio in the cylinders?

Also, if there is a big volume difference in the cylinders and the flow area on the control is adjusted to compensate and give the same cylinder stroke time, there will be a different margin at the pump and so the pump will control slightly differently in order to hold the 25 BAR margin.

As always, more info is required to help further.

 

[Jacc]

Thanks for the replies guys! When I say response I mean acceleration. Speed is not the problem. Acceleration, or rather the lack of it, is the problem.
Piston side volume is about 700 L but since that is already compressed by the weight of the boom it does not contribute to what I think is the problem.

 

[TEguy]

Perhaps give us a circuit of your set up.