low and high pressure accumulator

[mawad]

Dear All,
I have a question and I would be grateful if you can help me to find its answer. I saw in some hydraulic circuits they use 2 accumulators for both high and lower pressure. I don't understand why they use two. I would be grateful if you help

 

[BrianPetersen]

If two parts of the system have two different operating pressures (which could happen for a multitude of reasons) and they each need an accumulator ... two it is.

 

[zeusfaber]

Can't say I've ever seen it, but you could imagine a system that wants to be ripple-free about either of two different pressures (you might call them "on load" and "off load"). If the LP accumulator shell is rated to take the high pressure and the precharge on the HP accumulator is higher than the LP working pressure, it ought to work.

More likely to be what Brian said though.

A.

 

[hydtools]

If you have a sealed, non-vented reservoir you may use a low pressure accumulator connected to it.

Ted

 

[mawad]

Actually, it was for hydraulic fatigue testing machine. The two accumulators were connected to the cylinder which was controlling the force and the load. The load varies during the testing cycle in cyclic load .

 

[mawad]

Is there a guide for the calculations of the high and low accumulator to use it in fatigue machine

 

[hydtools]

A system schematic and operation parameters would be most helpful for anyone here to offer guidance.

Ted

 

[BrianE22]

If there are dynamics then you would use a LP accumulator along with a check valve to maintain some pressure (typically 100-200 psi )in the return line. Without it and with high dynamics you can create negative pressure and cavitation in the return line.

 

[mawad]

I don't have circuit diagram and I need to design a circuit for hydraulic fatigue machine. I am wondering where can I find help and guide in designing such hydraulic system. I saw a photo for fatigue machine and I found they use 2 accumulators.
@Brian. Yes, there are dynamic loads during the testing

 

[BrianE22]

Is it an MTS or Instron type servo-hydraulic fatigue machine? 3000 psi hydraulic pressure? Typically you would purchase a Hydraulic Service Manifold (HSM) and install close to the testing machine. HSMs come with HP and LP accumulators, filters, on/off valve, check valves etc. All you need to do then is install hydraulic lines to the HSM from the pump and from the HSM to the testing machine.