Why can't I adjust the proportional band on a pump?

[PNachtwey]

I can't believe it? You hydraulic people put up with what ever garbage the manufacturers give you.

I want to adjust the proportional band of a pump so I can set the band to be 0% at 1500 psi and 100% flow at 1400 psi or even 1450 psi. If I can I like to know how. If not I would like to know what is wrong with you guys?

 

[PNachtwey]

You also have to consider the use of a torque and speed sensor depending on the type of motor and pump setup to verify the output of the VFD matches the actual delivery of the pump.

The VFD is driving the fixed displacement pump. The speed of the VFD and the pump are the same because they are on the same shaft so the flow is proportional to the rate of rotation of the VFD. There is an encoder on the shaft so one can equate 4000 ( just and example ) encoder counts to what ever the pump flow is per revolution. Next a gear ratio needs to be set up between the line flow and the VFD rotation rate. Now the pump will always output the average amount of oil for that line speed no matter what the line speed is. Accumulators can keep the pressure constant within a cycle. However, a more sophisticated controller could vary the speed and a function of the production line feed rate. This would be the ultimate because the pump would always be supply the correct amount of flow ( very close anyway ) for any part of the cycle as a function of line speed.

I would still have a pressure sensor and small accumulator for correcting small errors. For instance if the gear ratio if off by 0.01% it may not be noticeable for a few hours but eventually the pressure would stray from the desired. A pressure sensor could be used to make fine adjustments in the gear ratio. Also fluid expands and contracts as a function of heat so there is always be a need for fine adjustments but at least one doesn't have to wait for the system pressure to drop 300 PSI before the pump starts to supply the rated amount of oil.

Think about this. If I want a pump to supply 10 GPM at 50 PSI drop I must buy a 60 GPM pump at 300 PSI drop. That is a waste. This assumes the pumps swash plate response is linear.

 

[budt]

Peter;

Are you getting any closer to understanding of why I have been pushing for TRAINED/DEDICATED FLUID POWER PERSONS for 20 plus years?

Not much in Fluid Power Training or Fluid Power implementation has changed in those years so it is either a bad Soap Box to be on or someone is fighting progress.

I still have hopes that the situation will change or at least will be recognized before Fluid Power is replaced like the Line Shaft Systems of the 20's.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[EdDanzer]

The actuator gain should change very little if you are metering out with your valves if they have a fast response time and some metering capabilities.

Why do you choose such low operating pressures? In the mobile world 5000 psi is standard on excavators with 250 psi load sensing hp compensated pumps.

Most inexpensive swash plate pumps have a piston moving the plate angle. There are limitations on how fast the plate can move before the pistons want to pull away. The piston valves have small passages to restrict the speed change can happen

I think one version of the Kawasaki pump has a plate to hold the pistons down and is available with electronic controls. This pump at 4000 to 5000 psi coupled with high speed meter out valves should provide a stiff more linear system than a 1500 psi can ever have.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com