Specifying the right cylinder for the job results in better and longer cylinder performance. This means lower overall operating costs.
Proper cylinder sizing starts with a calculation:
- Load weight
- Required speed
- Air pressure to be used.
Load weight: This is set by the design of the machine. In order to move the load, you obviously need a cylinder that provides more force than the load. We recommend allowing an additional 25% force on the load to compensate for friction.
Speed: Speed is usually set by machine design as well, but usually has some degrees of freedom within a range. Low speeds (up to 4 inches/second) require 25% more force than the load, medium speeds (4 to 16 inches/second) about 50% more, and high speeds (greater than 16 inches/second) about twice as much.
Air pressure: You need consistent airflow at the minimum effective pressure to maintain the desired speed. Operating the cylinder at too high a pressure will accelerate seal wear and create pressure on the cylinder. Inconsistent pressure can lead to system malfunction or failure.
Next, you need to determine the orifice size. Let's look at an example, assuming a maximum load of 100 lbs, a minimum speed of 8 in/sec, and a minimum pressure of 60 psi. The speed is moderate, but the force should be about 50% over the load, or 150 lbs. Dividing the force (150) by the pressure (60) gives a power factor of 2.5.
A 2″ bore cylinder with a power factor of 3.1 will provide the required force. You must also consider stroke length, spring force, and overall dimensions of the space. But that's just the beginning.