Screw pumps are divided into:
A single screw pump is a pump in which a single screw engages and rotates in the internal thread groove of the pump body.
A twin-screw pump is a pump that transports liquid by interlocking two screws.
A three screw pump is a pump that transports liquid by interlocking multiple screws.
Single screw pump
It is a single screw transport pump, whose main working components are the eccentric spiral screw (referred to as the rotor) and the screw liner (referred to as the stator) with a double helical surface on the inner surface. Its working principle is that when the motor drives the pump shaft to rotate, the screw rotates around its own axis on one hand, and on the other hand, it rolls along the inner surface of the liner, thus forming a sealed chamber of the pump. With each rotation of the screw, the liquid inside the sealed chamber advances one pitch forward. As the screw continues to rotate, the liquid spirals from one sealed chamber to another and finally squeezes out of the pump body. Screw pump is a new type of mechanical device for conveying liquids, which has the advantages of simple structure, safe and reliable operation, convenient use and maintenance, continuous and uniform liquid output, and stable pressure.
Double and multiple snails
Taking three screws as an example.
It is mainly composed of a liner (pump cylinder) fixed in the pump body, an active screw inserted in the pump cylinder, and two driven screws engaged with it. Three interlocking screws form a sealed chamber in the pump cylinder according to each lead, creating a seal between the suction and discharge ports.
When the pump is working, due to the symmetrical meshing between the two driven screws and the driving screw, the radial force acting on the driving screw is balanced, and the driving screw does not bear bending loads. The radial force acting on the driven screw is supported along its entire length by the pump cylinder liner, so there is no need to install additional bearings at the outer end, and it basically does not bear bending loads. During operation, a layer of oil film is formed between the outer surface of the screw and the inner wall of the pump cylinder, which can prevent direct contact between metals and greatly reduce the wear of the screw tooth surface.
When the screw pump is working, the suction and discharge pressures of the liquid are applied at both ends, thus generating axial thrust on the screw. For pressure differentials less than 10 kgf/cm2Small pumps can use thrust bearings. In addition, high-pressure oil is introduced into the bottom of each screw shaft sleeve through the central oil hole of the active screw, thereby generating a balanced thrust opposite to the axial thrust direction at the lower end of the screw.
Like other positive displacement pumps, when the discharge port of the pump is closed, the pressure inside the pump will rise to a dangerous level that could damage the pump or overload the motor. So, a safety valve must be installed at the suction and discharge ports of the pump.
The shaft seal of screw pumps usually adopts mechanical shaft seals and can take different forms according to the working pressure.