Calculating Valve size with accumulator

[Tom.C]

Hey everyone, Hope you're all doing well.

So I have been trying to wrap my head around this and seem to be stuck at this point, I am trying to determine what size hydraulic valve I need to incorporate into my system, the valve is intended to be a vent to open slip in logic valve, It will supply flow pushing a cylinder with a weight attached in order to accelerate the weight to a specific velocity. The accumulator will step in as the prime mover due to the short time of the cycle the pump will only supply a small amount of flow.

This is the data I have.
Final velocity needed of actuator
Surface area of piston
volume of blind and rod end (these are equal because the cylinder is double rod)
Minimum force to accelerate in given time/ distance ( this number can be flexible)
Supply pressure
Accumulator volume and precharge
Pump Flow constant
approximate flow from accumulator per 100 psi drop
fluid gravity
fluid temperature

So I have read about finding the "Cv" or flow coefficient however i am not sure how to apply it. I know that as my valve opens the pressure supplied via accumulator will drop this will in turn change the Cv no? furthermore, I don't fully understand how to calculate the demand from the actuator, I know how many gallons per minute it will require to accomplish the stroke I don't know how that will effect pressure or how to calculate a pressure drop. It seems like I will have to find a "median" point and go over/under IE size the valve for an average acceleration to meet my final velocity goal.

 

[PNachtwey]

I have written a series of articles in Hydraulics & Pneumatics magazine about this very topic.
I have a program that I use for sizing hydraulic servo systems.

https://www.eng-tips.com/viewthread.cfm?qid=468941

Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/

IFPE Hall of Fame Member

 

[Tom.C]

Yeah that calculator looks excellent, how can I gain access to that?

 

[PNachtwey]

Right now, no.
We don't have the program web based yet and it would be foolish to let it out in the wild without compensation.
You need to read the H&P articles. Search for my name.




Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/

IFPE Hall of Fame Member

 

[Tom.C]

I agree that it would, im sure this took a lot of your time to make, it surely would be a great resource for engineers to avoid some of these complex math equations and calculations, Thanks for the reply. I will definitely go follow your work on H&P and will be looking forward to seeing more about that software!

 

[PNachtwey]

This is used to support our customers that use our hydraulic servo controllers.
I agree though. A few engineers with my software could size all the hydraulic servo systems in North America easily.



Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/

IFPE Hall of Fame Member

 

[LittleInch]

Cv of a valve is fixed. The pressure drop will change as flow changes. Unless this is a variable control valve?

For this you are probably best using an accumulator which only uses 10-15% of its capacity per iteration before being refilled. Then the pressure should stay more or less constant.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Tom.C]

The valve will be an on/off valve, there will be no metering function other than a tuning stud, Due to the nature of the application 10-15% of the volume will not be possible because of the size accumulator that would require.

The valve will turn on and off very quickly I am thinking I may have to accelerate the cylinder much faster than the straight on paper calculation at first and as the pressure drops it will fall below that calculation as well and the average number will be the target.