Multi-stage centrifugal pumps rely on changes in the volume of the pump chamber to achieve suction, compression and exhaust, and rely on the rotation of the impeller to obtain centrifugal force. Multi-stage pumps are a type of centrifugal pump.
Multi-stage centrifugal pumps are divided into types and types according to structure
Multi-stage centrifugal pumps can be divided into many types according to the structure, and each structure has a different principle.
One, trochoidal type
A rotor with a trochoidal profile is installed eccentrically in the multi-stage pump cavity, which rotates along the inner wall of the pump cavity and divides the pump cavity into two variable volumes. The pump has good dynamic balance, so the operation is relatively stable, the vibration is small, the speed can be increased, and it can be small in size and large in pumping speed. It is suitable for developing into a mechanical multistage pump with high pumping speed. Due to the short and thick suction pipe, it is beneficial to increase the pumping speed of the multi-stage pump at low pressure
Two, fixed piece type
The fixed-vane multi-stage pump is equipped with an eccentric rotor close to the inner surface of the multi-stage pump in the pump casing. The pump casing is equipped with a radial sliding vane that always contacts the surface of the rotor. When the rotor rotates, the sliding vane can move up and down. Sliding divides the multi-stage pump chamber into two variable volumes. The fixed-vane multi-stage pump has a low pumping speed, which can be divided into single-stage and double-stage. The ultimate vacuum of the pump can reach 10-1Pa. Multi-stage pumps have simple structure, long service life and easy maintenance, but because their performance is not as good as rotary vane pumps, they are rarely produced and applied at present
Three, rotary vane type
The rotor of the rotary vane multi-stage pump is installed in the multi-stage pump casing with a certain eccentric distance and is close to the fixed surface of the inner surface of the pump casing. Two (or more) rotary vanes are installed in the rotor slot. When the rotor rotates The rotary vane can slide back and forth along its radial groove and is always in contact with the inner wall of the pump casing. The rotary vane rotates with the rotor to divide the pump cavity into several variable volumes. Rotary vane pumps are low-level multistage pumps. It can be used alone or as a backing pump for other high vacuum pumps or ultra-high multi-stage pumps. Rotary vane multistage pumps are mostly medium and small pumps, and the products have been serialized. There are two types of rotary vane pumps: single-stage and double-stage. Generally, two-stage pumps are used to obtain higher pumping power. Most of the rotary vane multistage pumps have a single working chamber structure. Two radial sliding vanes are commonly used, and three inclined sliding vanes are also used. Through-slide multi-stage pumps are also used.
Four, slide valve type
The slide valve type multi-stage pump is equipped with a slide valve outside the eccentric rotor. The rotation of the rotor drives the slide valve to move and roll along the inner wall of the pump housing. The slide valve on the upper part of the slide valve can slide in the swingable slide valve guide, and The multi-stage pump chamber is divided into two variable volumes. The pumping principle of the slide valve multistage pump is similar to that of the rotary vane pump, but the structure of the two is different.
Slide valve pump uses a slide valve mechanism to change the volume of the suction chamber, so it is called a slide valve multi-stage pump.
Five, multi-stage jet pump
Usually a single-stage ejector is composed of two or more ejectors and condensers connected in series, which is called a multi-stage ejector pump. The role of the condenser is to partially condense and remove the condensable steam in the mixture to reduce the load of the downstream ejector.
The condenser is installed before the inlet of the first-stage ejector, mainly to reduce the load of the first-stage pump. It can be used only when the pumped mixture contains a large amount of condensable steam and its partial pressure is stronger than the saturated steam pressure corresponding to the cooling water temperature. The intermediate condenser is installed in the middle of the multi-stage pump. The specific position should be determined by the partial pressure of steam and the temperature of the cooling water in the mixture entering the condenser. Its function is to reduce the load of the lower pump. The rear condenser is installed after the final ejector, mainly to eliminate the exhaust gas and noise of the final ejector, and is sometimes used to recover the waste heat of the final ejector.
