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Converting a Variable Displacement System to Fixed

Converting a Variable Displacement System to Fixed

Converting a Variable Displacement System to Fixed

(OP)
Hi All,

I have a Rexroth AA10VSO Series 31 hydraulic variable displacement, axial piston pump (please see attachment)
The reason I want to convert it to fixed displacement is because we don't need any variable output anymore. we will have a mechanical softstart for the hydraulic.
Also we need to reduce numbers of electrical control on our system.

Sorry, I'm not an expert in hydraulic. My question is how can I energize the pilot pressure? below is the snapshot from the datasheet.



Below is a snapshot from our existing hydraulic system and items in red circle are the control manifold which we will eliminate. can i just introduce a tee after 'LR'. one outlet to the 'x' (with pressure limiter) and the other outlet to the system?



thank you for your help in advance.

R.Efendy

RE: Converting a Variable Displacement System to Fixed

Not sure what a mechanical softstart is?
But one problem with not having a variable displacement on the pump is that when you start the motor for the pump, you want the output to be as low as possible in both pressure and flow, otherwise the start current on the motor will be to high and it will start tripping, if it even is possible to start it at all.

Best Reagards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

RE: Converting a Variable Displacement System to Fixed

Contact Rexroth to ask if they have a kit to convert the pump to fixed displacement.

Ted

RE: Converting a Variable Displacement System to Fixed

Currently the pump is a variable displacement with electrical proportional pressure control. In other words, it will swivel down when the pressure setting is reached.

You should be able to remove the electrical proportional valve and plug the line to the pump since there is still a DR regulator as base.
It will then still be a variable displacement pump but the pressure setting will now be fixed and can be adjusted on the pump regulator.

Another option if you are in doubt is to simply replace the electrical proportional valve with a mechanical one.

RE: Converting a Variable Displacement System to Fixed

(OP)

Quote (RedSnake)

Not sure what a mechanical softstart is?
same theory as to reduce the starting current. we use it to avoid high starting current as well by allowing the pump to produce a smooth pressure/flow before running at full capacity automatically by the mechanical soft start.

R.Efendy

RE: Converting a Variable Displacement System to Fixed

(OP)

Quote (Jacc)

Currently the pump is a variable displacement with electrical proportional pressure control. In other words, it will swivel down when the pressure setting is reached.

You should be able to remove the electrical proportional valve and plug the line to the pump since there is still a DR regulator as base.
It will then still be a variable displacement pump but the pressure setting will now be fixed and can be adjusted on the pump regulator.

Another option if you are in doubt is to simply replace the electrical proportional valve with a mechanical one.

I definitely have to eliminate the electrical proportional manifold as it may interfere with my newly system arrangement due to limited space and the reason i mentioned earlier.
I really appreciate your idea. We will definitely give a try on regulating the regulator on the pump later. Adding a mechanical control valve will involve too much new design as our system needs to be unmanned and dive into the sea.

R.Efendy

RE: Converting a Variable Displacement System to Fixed

(OP)

Quote (hydtools)

Contact Rexroth to ask if they have a kit to convert the pump to fixed displacement.
yes I may. They may have different ideas too.

R.Efendy

RE: Converting a Variable Displacement System to Fixed

A system with a variable displacement pump has a directional valve system with a closed center. IF you want to convert it to a fixed displacement pump you will need a directional valve with an open center so the entire pump flow can be dumped or by-passed to the tank when no hydraulic function is needed. When flow is directed to a function/actuator the pump will stay in max flow till it reaches the "cut off" pressure setting of the pump compensator.

You say you "don't need a variable flow anymore"?! Does that mean you are also rebuilding the system including the directional valve system?

Quote (OP)

My question is how can I energize the pilot pressure?
If you energize the pilot pressure the pump will de-stroke and deliver zero pump flow.

RE: Converting a Variable Displacement System to Fixed

Converting to fixed displacement is going to increase the fluid heating substantially. Be sure you're system can handle the extra heat input.

RE: Converting a Variable Displacement System to Fixed

This is how the pump manages the pressure with the compensator


Disconnect the compensator and plug the ports/holes in the pump housing and the pump can't destroke

RE: Converting a Variable Displacement System to Fixed

I don't think OP wants to convert it to fixed displacement, if you read between the lines he just wants to get rid of the proportional pressure control as that is no longer needed.

RE: Converting a Variable Displacement System to Fixed

Quote (BEMPE16524)

I want to convert it to fixed displacement is because we don't need any variable output anymore
I agree that it is a Q from someone that does not know a lot about hydraulics in general. That's why I tried to lay out some explanation "cards" about how these pumps works

Quote (BEMPE16524)

Sorry, I'm not an expert in hydraulic
And this question shows the ignorance

Quote (BEMPE16524)

how can I energize the pilot pressure?
So before we actually know exactly what OP thinks is possible to accomplish we need him to respond to our questions. We just can not assume, "across the globe" what he really mean

RE: Converting a Variable Displacement System to Fixed

(OP)

Quote (TugboatEng)

Converting to fixed displacement is going to increase the fluid heating substantially. Be sure you're system can handle the extra heat input.
sorry for the late response. no worry, the whole unit will submerge in sea water. we have done it thousands times. only this time we are not so lucky to have the variable type (2nd hand unit we bought from 3rd party)

R.Efendy

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