Pneumatics Pull force same as Push force?

[Dr.Gusta]

My team is basically building a crossbow to launch the ball. We are planning on using a pneumatic piston to pull the bow into loaded position. I calculated that a 2in bore piston could push 188 ish pounds. What I was wondering is if the pull force of the piston is the same, less, or more.

[Domtech]

The surface area of the pull side is reduced by the cross-sectional area of the piston rod, so the force is slightly less.

[Deke]

Extending a pneumatic cylinder has more force than retracting it. To calculate the retracting force you need to subtract the area of the rod from the area of the cylinder, then multiply the pressure to the area.

Since the retracting side of the cylinder has a rod through it, it has less force than the extending side.

[Mr V]

As others have mentioned the rod reduces the piston area so the retract force is less.

Here is a handy chart from Bimba that give the power factor and the approximate force created with a 60 psi input. http://www.bimba.com/global/library/technical-tips/power_factors.pdf

There is also one on page 20 of this booklet http://www.bimba.com/global/library/catalogs/bimba%20catalogs/bimbarefhandbook.pdf that was included in the KOP in the past. That page (and the entire booklet) includes some important design considerations that are well worth noting. For example there is a page on how to calculate the approximate extension speed of the cylinder and how to maximize it.