Air Cannons
There are two special type of pistons used in air cannons: close tolerance pistons and double pistons. While in close tolerance pistons, O-rings serve as a valve, O-rings are not used in double piston types.
Close-tolerance pistons have a number of disadvantages: They can swell and stick, their properties alter due to atmospheric changes, and they fit tightly in the cylinder with close tolerances. Backlash may suck some of the bin material into the valve which can cause the piston to stick.
Common features of double piston construction: They cannot swell and stick, they fit loosely in the cylinder (no tight tolerances), atmospheric changes do not affect them, and foreign material entering the cylinder doesn't cause sticking.
Read more about this topic: Piston
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