Determining fluid flow in a closed system.

[goodguy1405]

I have a tool that uses external hydrostatic pressure and internal fluid pressure to move a piston.( In static equilibrium) I have 2 check valves inside that allow the transfer of fluid internally from one chamber to another. I also have another regulated valve internally that allows .1gpm to flow from the check valves. The external forces acting on the tool is around 15000 lbf. My question is, How do I calculate the velocity the fluid will flow through the tool with the check valves and regulator valve? The internal piston moves through the fluid with only the pressure build up from the resistance of the check valves and regulator valve.

 

[LittleInch]

I've read this about four times and am struggling to make sense of it. Can you please sketch it out with sizes, flows, pressures etc and then you might get some sensible comments. It would appear quite simple, but is couched in so many confusing connections it is difficult to work it out or indeed why you want to know - Is there a problem or is this a question someone is asking you. It would be much better for you to work out what you htink it is and ask forum members to comment rather than expecting them to do your job....

just a thought

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[goodguy1405]

I am a mechanical engineer not a fluid dynamics engineer. Fluid dynamics as a whole is still a lost art. I am looking to get a close enough answer to what my calculations show in order to run the tool and get results. Like I said I am a mechanical engineer not a fluid engineer. I believe all my calculations are correct but I want someone to give their input to see if it matches my thinking and calculations. Their are 2 check valves on one piece. one allows fluid to flow one direction at a cracking pressure of 75 psi the other is a 0 crack in the other direction. These 2 valves feed through a .281 hole that has a flow regulator valve inside it that allows .1 gpm through it. I know this flow rate as I just stated is .1 gpm. I have external forces across a piston, subjected to hydrostatic pressures, of 20,000 lbf pushing fluid through the tool. I can't be real specific here about the whole idea for proprietary reasons. The fluid forces push across a 1" piston (internally) allowing it to move up inside the tool. The velocity of the fluid is my concern with the check valves and flow regulator inside. If the velocity is too high I could blow the seals out inside the tool. So my question is how to determine the velocity of the fluid in the tool? The knowns are: .1 gpm flow regulator, .75 psi cracking pressure check valve, 0 cracking pressure check valve, f= 20,000 lbf across a 2.5 inch piston externally, a force across a 1" piston internally.
unknown= velocity due to these external forces acting across a piston onto internal fluid pressures across a 1" piston.

 

[MikeHalloran]

Sorry, your word picture is not translating into any kind of diagram or drawing for me.



Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

Glad it's not just me.... If you know the flow, and the ID of the diameter of your hole or the piston, then this is simple no? The forces and cracking pressures are irrelevant if you are controlling the flow to your 0.1 USGPM

in your .281 hole its 10,5 m/sec, say 35 ft/sec

In your 1" piston it's 1.2 m/sec - 4 ft/sec

A sketch would really really help though....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[goodguy1405]

Thank you for your comments. It has helped immensely.

 

[hydtools]

Velocity inside will depend on piston area compared to piston rod area and net displaced volume. Are extend and retract active areas/volumes the same? Single-ended or double-ended?

Never heard of a mechanical engineer disavow knowledge of fluid statics and dynamics.

Ted

 

[goodguy1405]

2.38" piston pushing fluid across a 1" diameter rod in a distance of 4" with 20,000 lbf exerted on the 2.38" piston from the underside. I am entry level engineer going back to finish those particular classes lol. Statics I have fluid NO. extend and retract are the same on that particular piston. changes when dealing with check valves and flow regulator as the tool moves through the fluid in that instance. Check valves and regulator control the time before the tool moves and the time it moves when it begins moving with the .1gpm flow regulator.

 

[LittleInch]

Glad to help. Diagrams do help though....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[chicopee]

Draw a sketch with all the details. As a ME you should be able to do that.

 

[goodguy1405]

I would draw a sketch but for patent reasons I am not able to yet. Thanks for all the help.

 

[hydtools]

You are displacing 14.65 cu.in. Flow is 23.1 cu.in./min If velocity is constant for full stroke of 4 in., stroke time is .63 min. 4/.63 = 6.3 in./min piston velocity.

Ted

 

[LittleInch]

Sorry,

doing it too late last night - divide my answers by 60 as I forgot to change gpm into seconds.

velocity in your .281 hole is 0.168 m/sec

velocity in the 1" cylinder is 0.02 m/sec, but please check my calcs....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[hydtools]

LittleInch, your calcs are good.

Ted

 

[goodguy1405]

All looks good. Now I am sure the fluid forces across the 1" piston is enough to move the piston at the speed I am needing to accomplish the goal of moving a 2.01" top piston up from the hydrostatic pressure force across a 2.38" piston across the 1" rod. Thanks all....

 

[LittleInch]

Eh?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[hydtools]

Exactly.?

Ted

 

[goodguy1405]

I have a tool that is using hydrostatic pressure across a 2.38" piston on the bottom which pushes internal fluid a distance of 4" across a 1" rod attached to a 2.01" knob on top. Without being too specific. This hydrostatic force on bottom is greater than the hydrostatic force on top allowing the 1" rod to move upwards. My concern is blowing out the seals due to this force with the check valves and flow regulator inside the tool. I hope that clears it up some.....

 

[LittleInch]

Nope, but I'm glad you know what you're talking about...

Glad to help you out, I think....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way