Lift pumps, in which the water flows freely away from the pump, which performs lifting duty only.
Force pumps, which deliver the water under pressure.
Plunger pumps, in which a “plunger,” or “ram,” as it is sometimes termed, is used.
Piston pumps have a piston instead of a plunger.
A double acting pump is one in which water enters into and is delivered from the pump at each stroke of its piston or plunger, or, in other words, one in which, while water is being drawn in at one end of the pump, it is also being forced out at the other.
A single acting pump is one in which the water enters the pump barrel during one piston or plunger stroke, and is expelled from the pump during the next stroke, hence the action of the suction and of the delivery is intermittent, although the pump is in continuous action.
For very heavy pressures plunger pumps are generally used, the plunger being termed a ram.
The advantage of the plunger or ram is that it gives a positive displacement, whereas in a piston pump a leaky piston permits the water from the suction side to pass through the leak in the piston, to the delivery side.
Piston pumps possess the advantage that there is less difference between the contents of the pump and the displacement than is the case in plunger pumps.
The displacement of a piston pump is found by multiplying the area of the pump bore by the length of the piston stroke.