A triplex pump is a pump that contains three cylinders. A cylinder is a barrel and rod device used to push and pull pressurized fluid.
Triplex pumps fall into the category of reciprocating-style pumps. Reciprocating pumps move fluid via one or multiple plungers or pistons. A plunger is a rubber cap and shaf device that uses pressure to release stoppages. A pump piston is a moving component that uses piston rings to create a seal, and transfers force in order to eject or compress fluid in the cylinder. Reciprocating pumps are either duplex (two cylinders) or triplex (three cylinders). These pumps may be powered by steam or air, or via a motor or engine's belt drive.
Single- or Double-Acting
These pumps can be single-acting, meaning they operate via single or independent discharge and suction strokes. Triplex pumps can also be double-acting, meaning they create discharge and suction in both directions.