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Hydraulic cylinder emptying

Hydraulic cylinder emptying

Hydraulic cylinder emptying

(OP)
Hi,
I need some help with my problem:
I have an hydraulic cylinder filled with a volume V of oil.
I apply a force F on the piston to push the oil throuh a hole d.
How can I calculate the time for the cylinder to be empty?
Thank you

RE: Hydraulic cylinder emptying

I would recommend using Fluid Dynamics to calculate your emptying time.

RE: Hydraulic cylinder emptying

(OP)
It's for work, I have to design some single acting cylinders with spring return (something like the RCH series from ENERPAC), but I don't know what spring to use.
I think on starting with the same emptying-time/stroke and than move to the load.

RE: Hydraulic cylinder emptying

There are speed control valves for this purpose. No calculation, just adjust as needed.

RE: Hydraulic cylinder emptying

"I think on starting with the same emptying-time/stroke and than move to the load."

If you're trying to attain the same stroke for fill and empty, a spring isn't going to cut it. The spring needs to be substantially weaker than the whatever is filling the cylinder, which makes it substantially weaker for emptying.

TTFN (ta ta for now)
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RE: Hydraulic cylinder emptying

(OP)
I don't have any problem with the extension. I want that different cylinders (different bore), drain with the speed via spring.
For the spring stiffness lower than my pushing force, I have my pushing force are 300, 600 and 1000 KN, so no problem here.
This kind of cylinders works at 700 bar with a manual pump, and need to retract at the opening of the drainage.

RE: Hydraulic cylinder emptying

Hole d will act as an orifice or damper...

You need to know the area of the hole, the discharge coefficient for the hole (usually 0.62), the pressure drop and the density of the fluid.

The orifice flow equation will tell you the flow rate based on the above.

The pressure drop is just the pressure in the cylinder - if we set the downstream side to zero.

The pressure is a function of the area of the cylinder and the force in the spring = F = PxA

The force is not steady state though...

You will need the equation of motion for the spring mass system - The orifice is working as the damper

Once you know the flow rate, as a derivative of time - noting that the flow will change as the force imparted by the spring drops as a function of displacement - you can calculate the time to empty a cylinder of a given size...

Or you can do it empirically...and play with different springs and flow control valves until you get the speed you need.

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