Control option of Variable Displacement pump
Control option of Variable Displacement pump
(OP)
Hello All,
I have question regarding the control option of Variable displacement pump.
I was going through variable displacement pump technical configuration. It was mentioned that load sensing controlling option is better
than pressure compensated control. I realize that load sensing covers the pressure compensated control, but I would like to know why
load sensing is better option. In which case I really need load sensing control, and in which cases I can get away with only pressure
compensated control?
I have question regarding the control option of Variable displacement pump.
I was going through variable displacement pump technical configuration. It was mentioned that load sensing controlling option is better
than pressure compensated control. I realize that load sensing covers the pressure compensated control, but I would like to know why
load sensing is better option. In which case I really need load sensing control, and in which cases I can get away with only pressure
compensated control?





RE: Control option of Variable Displacement pump
Ted
RE: Control option of Variable Displacement pump
Thank you for replying.Lets say I want to lift a load with telescopic handler or forklift. what option would be good and why?
RE: Control option of Variable Displacement pump
You could do the same with a fixed displacement pump delivering your required flowrate.
Pressure compensation control attempts to maintain constant pressure by varying flowrate.
Ted
RE: Control option of Variable Displacement pump
LS pumps work best when the speed of the input is varied, otherwise you would be best to use a torque limiting controller.
RE: Control option of Variable Displacement pump
Ted
RE: Control option of Variable Displacement pump
RE: Control option of Variable Displacement pump
So far all shots in the dark.
Ted
RE: Control option of Variable Displacement pump
Thank you very much for responses. I was studying my material to respond. Well, the prime mover is transmission with pump drive drive ratio of 0.971:1 and torque capacity of 245 Nm. The transmission maximum input RPM is 3300, but engine rated speed is 2200 RPM.
As hydtools mentioned output device is a cylinder which has to lift 6000 lbs with telehandler.
RE: Control option of Variable Displacement pump
LS on its own will allow you to match the demand at the cylinder, but if that exceeds the engine torque limit the engine will lug down.
When you purchase the pump, tell the supplier that you want 245Nm and they will set the compensator to that value. Then, if ever your load goes high while the pump is at a displacement that exceeds the torque, the controller will back the displacement off automatically.
Under that torque curve, the LS compensator will match the pump flow to the speed requirement.
You will need a valve that has an LS output that you can feed back to the pump to control it.
RE: Control option of Variable Displacement pump
Are you powering more devices than the one hydraulic cylinder? If not, adjust the pump displacement stop to deliver the flow you need for the cylinder and you will not need the load sensing control.
HPost, will not the two controls give conflicting commands? Load sensing trying to increase displacement to maintain flow while torque control tries to decrease displacement to reduce torque demand. Can one control have priority over the other?
Ted
RE: Control option of Variable Displacement pump
The torque controller will back the pump off well before it reaches its corner power. If the pump is at low displacement and the pressure continues to rise, then the pressure cut off will limit the pressure.
If the controller and compensator settings are set too close together then the pump will be unstable, so the pressure cut off is usually set to the maximum working pressure of the pump. Well above the torque control setting.
This is the way that the Bosch Rexroth A10 pump works with the LA DS compensator.
Details of which can be found here...
https://www.boschrexroth.com/various/utilities/med...
RE: Control option of Variable Displacement pump
Hydtools, I honestly didn't get you what you are trying to say in first two lines of answer in today's response. And as you mentioned, apart from cylinder,same PTO would be used for orbitrol steering pump from priority valve.
HPost, I really have to look into this Bosch Rexroth A10 pump and LS compensator and a torque limiter.