Structural principle of multistage pumps

The multistage pump is a type of centrifugal pump that relies on the change in volume of the pump chamber to achieve suction, compression and exhaust, and on the rotation of the impeller to obtain centrifugal force. Multi-stage pumps can be divided into many kinds according to the structure, each structure principle is different.

First, the remaining oscillating type

The multistage pump cavity is eccentrically equipped with a rotor whose profile is the residual cycloid, which rotates along the inner wall of the pump cavity and divides the pump cavity into two variable volumes. The dynamic balance of the pump is good, so the operation is smoother, vibration is also small, the speed can be increased, the size can be small, pumping speed is large, suitable for the development of large pumping speed of mechanical multistage pump. As the suction line is short and thick, it is conducive to improving the pumping speed of multi-stage pumps at low pressure.

Second, fixed vane type

The fixed vane multistage pump is equipped with an eccentric rotor in the pump casing close to the inner surface of the multistage pump, and the pump casing is equipped with a radial slide that is always in contact with the surface of the rotor, when the rotor rotates, the slide can slide up and down to divide the multistage pump cavity into two variable volumes. The multi-stage pump has a simple structure, long service life and easy maintenance, but because its performance is not as good as the rotary vane pump, so it is rarely produced and used.

Third, rotary vane type

Rotary vane multi-stage pump rotor with a certain eccentric distance installed in the multi-stage pump casing and the pump casing inner surface of the fixed surface close to the rotor groove is equipped with two (or more than two) rotary vane, when the rotor rotates the rotary vane can slide along its radial groove back and forth and always in contact with the pump casing inner wall, this rotary vane with the rotor rotation, the pump cavity can be divided into several variable volume. The rotary vane pump is a low multi-stage pump. It can be used alone or as a pre-stage pump for other high vacuum pumps or ultra-high multistage pumps. Rotary vane multistage pumps are mostly small to medium sized pumps and the products have been serialised. Rotary vane pumps are single-stage and two-stage, generally made into two-stage to obtain a higher pumping degree. The vast majority of rotary vane multi-stage pumps are single working chamber structure, commonly used two radial slider, also useful for three oblique slider. Through the sliding vane multi-stage pump also has the application.

Fourth, the slide valve type

Slide-valve multistage pump is equipped with a slide-valve outside the eccentric rotor, rotor rotation drives the slide-valve along the inner wall of the pump casing sliding and rolling, the upper slide-valve stem can slide in the swinging slide-valve guide, and the multistage pump cavity into two variable volume. The pumping principle of the slide-valve multistage pump is similar to that of the rotary vane pump, but the two structures are different. Slide-valve pump is the use of slide valve mechanism to change the volume of the suction chamber, so called the slide valve multi-stage pump.

Fifth, multi-stage ejector pump

Often single-stage ejector by two or more ejectors and condenser in series, known as multi-stage ejector pump. The role of the condenser is the condensable steam in the mixture is partially condensed and removed to reduce the load on the next level of the injector.

The condenser is installed in front of the inlet of the first stage injector, mainly to reduce the load on the first stage pump. It is only used when the pumped mixture contains a large amount of condensable vapour and the partial pressure of the vapour is greater than the saturation vapour pressure corresponding to the cooling water temperature. The intermediate condenser is installed in the middle of the multi-stage pump, depending on the partial pressure of the steam in the mixture entering the condenser and the temperature of the cooling water, its function is to reduce the load on the lower stage pump. After the condenser is installed in the final stage after the injector, mainly to eliminate the exhaust gas of the final stage injector, noise, sometimes used to recover the waste heat of the unstaged injector.