What is marine screw pump? Screw pump is a kind of rotary positive displacement pump, and it is widely used on board. The pump can draw and discharge liquid due to the rotating of the rotors in the pump. According to the number of the rators, there are single screw pump, twin screw pump and triple screw pump…
Triple Screw Pump Working Principle
The pump mainly consists of pump casing, inner rotor housing and three rotors. Fluid is trapped within a series of successive helical cavities that are formed between the threads of the three screws and are sealed by a close-clearance casing. As the vacant cavities increase within each rotor spin at the casing’s suction port, vacuum is created that draws additional fluid into the pump. The meshing of the rotors results in the formation of sealed cavities that progress axially along the path of the casing and carry fluid from the inlet port to the discharge port.
The return of fluid back to suction port is referred to as “slip”, which is impeded by close internal clearance. Therefore, maintaining a proper radial clearance between the rotors and the inner wall of the casing is very important to control the slip. The thermal expansion and the friction between the rotor and the inner wall of the casing should be taken in to account, and the clearance is about 0.016√D(D is diameter of screw) in most cases.
In order to prevent the external leakage, shaft penetrations in rotary pump casing are usually sealed with packing or mechanical seals. A mechanical seal is usually consists of a stationary ring, a running ring, rubber ring and a spring. The stationary ring is made of hard material while the running ring is made of elastomeric material.
