## 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

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

## RE: Hydraulic cylinder emptying

TTFN (ta ta for now)

I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

## RE: Hydraulic cylinder emptying

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

## RE: Hydraulic cylinder emptying

## RE: Hydraulic cylinder emptying

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)

I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg

FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

## RE: Hydraulic cylinder emptying

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

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.