A duplex pump is a pump typically found in waste water treatment plants and oil fields. It consists of two pumps that alternate the pumping process, thereby allowing it to be more efficient than a single version. This pump has a higher flow rate due to its not having a dead spot in the pump stroke. As one pump is completing its stroke cycle, the other is beginning its stroke — maintaining maximum pumping action without a break in the cycle.
The first duplex pump was steam operated. It consisted of two steam chambers as well as two pump housings. The pumps were capable of pumping twice as much liquid as a single-stage pump. There are no dead spots in this type of pump. The pumping cylinders are constantly under pressure and operate just enough out of time with each other to ensure that one or the other is always pumping.
The steam-operated pump was replaced with a duplex pump, which operates on compressed air. The compressed air acts in the same manner as the steam and maintains constant pressure on the cylinders of the pump. The original steam duplex pump was created in the 1800s and steam-operated pumps are still in use, but compressed air has taken over as the primary operating system.
The duplex pump is used where a high volume of sustained pumping is required. Waste water treatment plants utilize the pumps because of the need to move large quantities of water without the threat of backwash. Any backwash could potentially contaminate large freshwater storage tanks and render the system unfit for use.
In oil fields, the need to pump large quantities of water to cool drilling heads as well as to flush out the boring holes requires the use of a duplex pump. The ability to move the great quantity of water allows the drilling rigs to operate at a much faster pace than those equipped with a single-stage pump.
Duplex pumps are also used to pump diesel fuel and heating oils that do not require heating. The thin viscosity of these oils allow the pumps to transfer them to holding tanks as well as to pass the oils through a strainer to clean them of impurities. Thicker oils require heating to allow them to be pumped. The thin make-up of the heating oil allows the oil to flow freely through the pumps at a high rate.