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Hydraulic Calculations


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While researching hydraulic forging presses, I came across some nifty calculations. These should help with the setup and aquisition of the parts needed. I hope.

Sizing the electric motor

Hp = (Q x P) / (1714 x Em)

Hp = Horsepower
Q = gpm flow
P = pressure psi
Em = pumps mechanical efficiency

As an example, say you had an 85% efficient 13 gpm pump and a 2500 psi rated cylinder.

(13 x 2500) / 1714 x 85%) = Hp
This combo would require a 4.4 hp motor to operate.

A funny note to add is that some pumps are considered two stage. At the beginning stage, you get full flow, and once the pump encounters resistance, that flow drops. Ofcourse, at high flow, you get the best speed, and at the lower flow you get the most power but slower speed.

But you don't know what size cylinder you need? There's a calculation for that too!! Amazing!!

Say you want your end product to be a 40Kpsi press for mashin metal. This is a two part equation.


Ap = F / P

Ap = cross section area of piston in cylinder
F = force required
P = pressure supplied by pump

Ap = 40,000 / 2500
Ap = 16


Dp = Sq root of 4 x A / pi

Dp = diameter
4 = constant
A = cross section area
pi = 3.14

Dp = 4 x 16 / pi
Dp = Sq root of 20.382....
Dp = 4.5

You would need a 4.5" dia cylinder.

Its pretty basic, but I hope that it helps with any research anyone is doing when thinking about stepping up to a hydraulic press. There are alot of safety variables involved in building your own as you would imagine. Care should be taken when building a machine such as this.

If I did anything wrong, I would hope that some of the seasoned pro's would chime in. :)

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