What is a Duplex Pump?

A designation of a reciprocating pump that uses two drive rods.

Duplex pumps are common in both single and dual acting designs. Due to some of the benefits over simplex pumps, and simpler design than other reciprocating pumps, they are often a preferred pump for many applications.

Essentially, a single action duplex pump is two simplex pumps running at 180 degrees from each other. As one plunger or piston is pumping fluid into the outlet port, the other is drawing in from the inlet. A dual action is similar in style but is only offset at 90 degrees. Theoretically, a dual action duplex operates using four single-acting plungers or pistons. Keeping the rotation at 180 degrees would create two overlapping sets of plungers or pistons. A 90-degree offset helps to stabilize the flow. See the flow characteristics below for more information.

Duplex Pump Flow Characteristics

Duplex pumps have a steadier flow than simplex pumps. However, their flow still has a large variation. In a single action duplex pump, the maximum flow velocity is 160% of the average. That is, every rotation of the crankshaft, the flow varies from 0% to 160% of the average flow rate. In a double acting duplex pump, the maximum flow velocity only varies between 111% and 79% of the average flow rate.

Note that the dual action charts are made specifically for a plunger pump. In a dual action piston pump, pump chambers one and three would look similar to that shown above, but chambers two and four would have a slightly lower relative velocity. This is due to the fact that one side of the piston requires the drive rod, reducing the usable volume within these pump chambers.

Duplex Pump Example Applications

Duplex pumps are used in low flow applications across many industries. Several example applications may include:

  • Crude Oil Transfer
  • Hydrocarbon Condensate Collection
  • Coke Oven Tar
  • Bauxite Slurry
  • Salt Water Disposal
  • Hot Oil
  • Cement
  • Aluminum Ore Slurry
  • Coal Slurry
  • Cryogenic Service
  • Steam
  • Ore Slurry
  • Drilling Mud

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