Positive displacement pumps are the pumps that provide flow and pressure to the outside, which are conventional pumps. A negative displacement pump is a hydraulic motor that runs on external pressure and flow. Positive displacement pumps are self-charging. Unlike centrifugal or turbo pumps, flow is constant regardless of system pressure drop.
Structural Characteristics and Application of Positive Displacement Pump
Compared with centrifugal pumps, positive displacement pumps have high delivery pressures. There are two types of positive displacement pumps: piston pump and plunger pump. The maximum pressure of the plunger pump is 24-28MPa, and it is equipped with a clean water flushing system to ensure that there are no abrasive solid particles on the plunger during the working process. The piston pump has a larger delivery flow, but the delivery pressure is lower than that of the plunger pump, and the maximum pressure is 17-20MPa.
The positive displacement pump consists of two main parts, namely the power end and the infusion ends.
The power end part converts the rotational motion of the prime mover into the reciprocating motion required by the infusion end part. For the plunger pump, the infusion end generally consists of three single-acting plungers, a single or integral parallel working cylinder, and a suction valve and a discharge valve for each cylinder. The plungers in the three working cylinders are at an angle of 120° and reciprocate, and their volumes increase and decrease alternately, so as to achieve continuous suction and discharge. In piston pumps, a single- or double-acting piston replaces the plunger.
The parts that are often worn in positive displacement pumps are valves, valve seats, piston or piston seals, plunger or cylinder bushings, etc. For highly abrasive slurries, the life of these consumables is typically only a few hundred hours. Therefore, the short life of wearing parts and the high cost of spare parts are one of the disadvantages of positive displacement pumps.
The twin-screw pump independently developed by our company has effectively overcome this problem, greatly extending the life of the pump and improving economic benefits.
The positive displacement pump is the main pump of the long-distance slurry pipeline. After a long-term test abroad, the performance is relatively good.