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Unread 12-01-2002, 18:54
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Ghetto_Child Ghetto_Child is offline
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Pneumatic equations

I am making a xls for my team regarding pneumatics.

PLEASE PLEASE PLEASE!!!!!

Does anyone have equations?

I need all types and as many as possible.

Thank you.
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Unread 12-01-2002, 19:49
Lloyd Burns Lloyd Burns is offline
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To find the force available from a piston, look it up in the pneumatics manual, or use the formula
P = F/A or F = P * A
where P : pressure, A : area, F : force

Don't forget that the area is different going either way; subtract the area of the shaft when calculating the force available to retract the shaft.


Work = F x d ..... Work, Force, distance
.......P * A x d . subst earlier eq'n
.......P * V ..... Volume (stroke * Area)

The work done depends on the pressure and the volume. Eg, for charging the reservoir; use 1/2 the final pressure to compensate for the changing pressure.

Now you know the work, and you can figure the pressure, so to calculate the power, divide work/time, which is equal to the pressure times the amount of volume change / time unit, as an approximation.

The pump probably draws about 8 A @ 12 V when running, or about 96 W , or about 2/15 HP. It won't run at 100% efficiency, so you'll get less.
Check the specs, for pressure and volume/sec to get an idea of the output.

You'll want to know how much air goes through your valves, for volume change in the cylinder calculations, realizing that there will be a pressure drop which gets bigger when the flow is more. At the end of the stoke, when the flow slows, the pressure drop gets less, approaching the system pressure, which may be the regulator set pressure, if the reservoir isn't depleted.

The gas Laws say PV = nR(a constant for a closed system) times the temperature.
The air in the reservoir at 120 psi, has as many molecules as a reservoir twice the size at 1/2 the pressure. Glitch: once you get to 60 psi in the reservoir, the regulator pressure, if the compressor doesn't do something, the next push will drop the available pressure, slowing you piston movement, and reducing the power of the stroke. The T fot temperature is part of the reason your pump gets warm. It is the absolute temperature; ask your teacher.

Is that enough formulae ?

As with everything in engineering, the skill is in knowing where the thing is likely to depart from the mathematical model, and compensating where neccessary for the amount of departure. This should give you a first approximation to a good answer.
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Unread 13-01-2002, 16:42
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thank you

Thank you, that helps a lot!
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