The delta P rating of a particular D03 proportional directional control valve is 145 psi at 4 gallons per minute. The valve serves as the control orifice for a load sensing (pressure and flow compensated) variable displacement pump. The flow compensator’s spring is set at 350 PSI. After the proportional valve spool shifts into a power envelope, at what flow rate will the pump begin to destroke?

Best Regards,
Bill O'Donnell

It is hard to determine because different types of pumps(different manufacturers) have different dimensions and those dimensions are not provided.

The pump control you are talking about is probably an electrically operated flow control(by means of a proportional pilot valve), with an auxilliary hydraulic pressure control(pressure compensator)... built in into the pump(in most if not all cases)?

Actually your statement is quite hard to analyze, until you can provide a circuit.

Some proportional valves are used to control pump flow, but normally the flow start at minimum(destroked/deadhead), then regulated(electrically thru prop valve) to a desired flow. The purpose of the compensator is to destroke/deadhead at maximum allowable pressure.

quote:

at what flow rate will the pump begin to destroke?

Recalculate the flow across the valve at the new pressure drop, assuming the spool is still in the same position. Once the pump achieves the 350 psi drop across the valve it will start destroking.

quote:

The pump control you are talking about is probably an electrically operated flow control

Maglub, the style control Bill is reffering to is like this 'flow compensating controller'
http://hydraulics.eaton.com/pr...s/E-PUPI-MC005-E.pdf

My pc is down.. I'm using my phone... But try rexroth a10vso...fed. It is equipped with prop Dcv, x'ducer,and hydraulic press controller.
The flow is min at 0 current and increases stepped with supply. Doug,the eaton u showed were just normal hydraulic flow/pressure control... A prop valve that controls pilot thru load sensing port would probably irrelevant since pump controls are pilot pressure dependent..
Most prop/servo control on pumps just Barry the pressure(varrying press drop on orifices) that will result to a variable back pressure on the stroking piston...
As u can see, the piloting of a regular flow/press comp is different from the electronically pilot control.

quote:

As u can see, the piloting of a regular flow/press comp is different from the electronically pilot control.

Bill isn't talking about electronically controlling the pump. It is a simple load sensing pump and the proportional directional control valve is being used as a variable orifice. The two together create pressure compensated flow control as the pump will always try to keep a 350 psi pressure drop across the valve.

Ok... If he is referring to the same set-up, the pump is destroked at center at 350 psi(deadhead setting of pump at neutral valve...Or any desired minimum).
When the valve is activated, the pump will re- destroke only at any load pressure+350psi. If the application is not precision, valve pressure drop will become insignificant once the pump swashplate is settled to the demand flow/actuator speed wrt load.

In a rexroth FED control(or any pump electronic control... probably), the pump is like a handwheel controlled, but just using prop/ servo pilot instead...

quote:

Originally posted by Peter Nachtwey:
Just curious.

What happens when the pressure is only 349?
Is the valve "off" when the pressure is below 350 psi?

The reason I ask is that just because the valve is rated for 4 GPM at 145 psid that doesn't mean that 4 GPM of flows at 145 psid when the proportional valve is open.

Is the proportional directional control valve fully open at 350 psi? The affects the answer.

Bill said the valve is a directional proportional valve. This probably means that the valve can move the swash plate both ways instead of using an opposing spring to return the swash plate.

One more point to think about. Not all valves have flows that scale nicely when the pressures or flows go above the rated values.

Bill, a link to the pump and valve pdf files would be helpful.

On or off function of the control valve is not dictated by pressure...I think you're confusing it with load sense stand-by pressure.

There are too many unknowns to answer his question. First of all, why do you have a valve that flows 4 GPM at just 145 psi being used for control pressure? That's way too much.

In a similar application, Bosch Rexroth requires just a 0.8mm orifice in the control path to their A10V pumps to limit saturation, when you can add a remote compensator to a load sensing pump. 0.8mm at 350 psi is around 1/2 gallon per minute. So why would you use a valve to supply control flow in the range of 6 GPM?

Gentlemen:

I thought there wouldn't be much of a response to my question. Thank you for taking time to write your thoughts.

The correct answer is 6.2 gpm, as Doug illustrates in one of his posts. And, as he writes in another post, the pump control type I'm talking about is a "simple load sensing" type.

My purpose in posting this question was to illustrate a point to a young colleague who has been in the FP business only a short time.

I told him (as I tell young colleagues frequently) that although there is accurate and precise terminology with which system details can be described, such terminology is not always understood as it is intended - not even by expert and experienced people in the fluid power business.

I insist to our rookies that it is essential that they learn all the correct terminology and that they learn incorrect terminology as well (because people use it), and that they learn how to describe a particular system detail in more than one way. I tell them that it is up to us as fluid power specialists/engineers to extract from our customers/clients the information we need, it is not up to the customers to spoon feed the information to us, and that it is up to us to explain to our customers what they need to know in terms they can understand. It is not up to our customers to learn all the technical terms we know.

It was my point in the post to show my young colleague that if I used text book terms like "load sensing", "control orifice", "delta P" "proportional directional control valve", "flow compensator", "power envelope", etc., each term would not be understood identically by everyone reading them - even among fluid power people. I am gratified that you gentlemen proved my point.

This is not a criticism of any of you. You made good points and asked good questions (which I'll be happy to discuss if you still want to). I hope you don't mind my using your responses as an illustrative lesson for a young man who is new to our fascinating field.

Thank you for responding.

Best Regards,
Bill O'Donnell

I could bring up the fact that the College of Hard Knocks training most in he Fluid Power Industry go through makes answering questions like these a little more difficult and understanding the different terms in the answers even more so.

BUT, I promised Peter I would not mention the fact that Fluid Power needs TRAINED/DEDICATED persons to apply it, similar to the TRAINED/DEDICATED persons applying Mechanical and Electrical systems.

Oh well.

quote:

BUT, I promised Peter I would not mention the fact that Fluid Power needs TRAINED/DEDICATED persons to apply it, similar to the TRAINED/DEDICATED persons applying Mechanical and Electrical systems.
Oh well.

This is still whining Bud.

I like a little Whine every now and then Peter. Helps me me get through my whaning years.