The role and type of multistage centrifugal pump pressure chamber
Multi-stage centrifugal pump press-out chamber refers to the space between the impeller outlet and the flange joint of the pressure water pipe. Its function is to collect the high-speed fluid flowing out of the impeller, and then introduce it into the pressure water pipe or the secondary impeller inlet with minimal resistance loss. The function of the press-out chamber is to correctly introduce the liquid to the next stage impeller or to the outlet pipe with minimal loss, while converting part of the kinetic energy into pressure energy. There are two types of multi-stage pump extruding chambers: spiral extruding chamber and annular extruding chamber.
Multistage pump
1. Spiral volute
Spiral extrusion chamber, also known as volute, collects the liquid flowing out of the impeller, and at the same time converts part of the kinetic energy of the liquid into pressure energy in the spiral diffuser. The spiral extrusion chamber has the characteristics of simple structure, convenient manufacturing, and high efficiency; however, it will generate radial force when operating under non-design conditions. It is mostly used in single-stage single-suction and horizontal split multi-stage centrifugal split pumps.
In the spiral volute, the gap between the pump tongue and the impeller should be appropriate. If it is too small, it will easily cause vibration and increase the noise near the dead point. After the liquid comes out of the volute chamber, it enters the diffuser. The diffuser angle of the diffuser is generally 6º~10º.
2. Annular push-out chamber.
The cross-sectional area of the flow passage of the annular extrusion chamber is equal, so the flow velocity is not equal everywhere, and the flow loss is large, so the efficiency is lower than the spiral extrusion chamber. It is mostly used in the water outlet section of multi-stage pumps or to transport liquids containing impurities.
3. Radial guide vane
It is fixed on the outside of the impeller outlet. The role of the guide vane and the volute, the front section only plays the role of collecting liquid. The liquid moves at a constant velocity in this section. Only when it reaches the diffusion part does part of the kinetic energy become pressure energy. Therefore, the guide vane can be regarded as being placed on the circumference of the impeller. Of several volutes.
In addition to the radial guide vanes, there are also runner-type guide vanes. They all have the same function but different structures. The flow-channel guide vane is an integral form, that is, liquid flows in the guide-vane channel from the inlet of the guide vane to the outlet of the suction guide vane. But it is complicated to manufacture, and generally not used much.
The comparison of multi-stage centrifugal pumps with volute extrusion chamber and guide vane extrusion chamber is as follows:
1. The volute pump produces large static head, low loss, high efficiency, simple structure, and the axial thrust can be balanced by symmetrically arranging the impeller. The guide vane pump is worse, and has a special balancing device.
2. The whole rotor of the volute pump can be assembled in advance and placed in the pump body. The guide vane pump is very troublesome to disassemble and assemble.
3. The outer diameter of the impeller of the volute pump can be reduced by 20%, which has little effect on the characteristic curve and efficiency, while the guide vane pump cannot, otherwise it will cause a lot of energy loss.
4. When the flow deviates from the design conditions, the motion state of the guide vane pump will change, causing the efficiency to drop rapidly, while the volute pump does not, and its efficiency is not significantly reduced in a relatively wide range.
5. Compared with the guide vane pump, the volute pump has the disadvantages that the casting is complicated, the axial length is large, the larger processing machinery is needed, and the radial force is generated, which must be balanced by structural measures.
