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High Viscosity Flow Through an Orifice

High Viscosity Flow Through an Orifice

High Viscosity Flow Through an Orifice

(OP)
Hello,

I am designing a closed hydraulic cylinder with high viscosity fluid. The piston in this cylinder forces fluid through orifices in the bottom of the cylinder, then up through a fluid return cylinder, finally back into the piston area through the same size orifice in the top of the cylinder.

I am having difficulty determining the appropriate size of the orifice.

What I do know is:
constant pressure on the piston
piston size
fluid properties

It seems reasonable to assume that by varying the orifice size I can find the appropriate speed I wish the piston to move.

Any suggestions or help would be greatly appreciated
Thanks!

RE: High Viscosity Flow Through an Orifice

But you can't change orifice plates without shutdown, draining, cleaning, disassembly, and full rebuild of the system, cleaning, and refilling/venting.

Isn't that going to cause a problem with schedule?

RE: High Viscosity Flow Through an Orifice

Use a needle valve like all the speed control valves now made. You will get the exact speed you need without calculation and will be able to adjust for dirt in the orifice, and viscosity changes with time and temperature.

RE: High Viscosity Flow Through an Orifice

(OP)
Thank you for your help

I should have attached a sketch originally, but here it is.
http://files.engineering.com/getfile.aspx?folder=3f5f321d-f20e-4793-bd60-78d53847c519&file=SimpleSketch.PNG
ProE drawing, colored to make it easier to see. Dark blue is fluid, light blue is the orifice. The rest of the body and piston is solid and sealed.

The cylinder is a very small damper, about 3" max height and 1" max bore size. The orifice total area per half of the cylinder will be less than 1/2" over 4 orifices, making each hole a mere 1/8" area.

The orifice values I just mentioned are my best guess on what I need based on the velocity I wish the piston to move when about 50psi is exerted on it.

However, I am looking for mathematical background for these guesses. My goal is to graph the average velocity of the piston over 1" displacement as it relates to the orifice size (simplifying my future decisions).

I am also assuming the temperature does not change, for ease of calculations, possibly to be looked at again in the future. Also there time dependent situation such that the velocity of the piston will not instantaneously change due to a pressure build up at the orifice. So an average velocity will do for now but any help into that next level would also be appreciated.

Thanks again for any additional help
 

RE: High Viscosity Flow Through an Orifice

How are you accounting for the change in cylinder volume as the piston rod moves in or out?  

RE: High Viscosity Flow Through an Orifice

(OP)
The total cylinder volume or volume of fluid will not change, the fluid only moves from the bottom to the top of the cylinder. As a control volume problem I am only considering half of the cylinder.

RE: High Viscosity Flow Through an Orifice

>>>The total cylinder volume or volume of fluid will not change, ...<<<  

Yes, but you are drawing the wrong conclusion.  You need to review how hydraulic systems, and especially cylinders, work.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: High Viscosity Flow Through an Orifice

Which is to say, if you build it as drawn, once you have removed all the air from inside, the piston rod will _not_ move, except as allowed by the bulk modulus of the fluid.

 

Mike Halloran
Pembroke Pines, FL, USA

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