Is the outlet pressure of a screw pump related to the length of the screw?
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Under normal operation, the outlet pressure of the screw pump remains stable; to adjust the outlet pressure, the outlet return valve can be slightly opened. Recently, I specifically sought out some information on this topic, which shows that the outlet pressure of a screw pump is related to the back pressure. This statement is consistent with the actual practices. However, the operating procedures state that the outlet pressure of a screw pump depends on the screw length; so what is the basis for designing the screw length? Is it really related to stress? Is there a specified minimum pressure at the pump outlet?
LZ, don’t confuse design with actual operation. When in use, the length of the screw in a screw pump is fixed; therefore, the pump’s outlet pressure has nothing to do with the screw length. What matters instead are the actual operating conditions, such as the inlet and outlet pressures； For screw pumps of the same specification, generally the longer the screw, the higher the discharge pressure. I have no experience in designing screw pumps, but when designing their length, the stiffness of the screw must definitely be taken into account. For example, if the displacement is low but the discharge pressure is high, the screw needs to be longer; in such cases, if stiffness is insufficient, intermediate supports must be added.
Perhaps I didn’t express myself clearly enough; what I’m asking is whether there is a relationship between the length of the screw and the pressure during design.
Yes. Its discharge pressure depends on the sealing length between the stator and rotor. Therefore, for the same rotor, the longer its length, the higher its discharge pressure ； The same is true in reverse. This is my understanding.
Sure, there is a connection. I’m not the one who designed it either
It is related; in addition to being related to the length of the screw, it is also related to the radial diameter of the screw rotor. Of course, it is also related to the rotor speed, as well as the temperature and viscosity of the medium being transported!
For each additional pitch, the outlet pressure increases accordingly. Outlet pressure refers to the pressure loss due to the resistance in the pipelines of the outlet system.
There is definitely a connection – one has to take into account the issue of pressure, as well as the strength of the screw, sealing, and efficiency; it’s necessary to find an optimal value in all these aspects.
It is related to the matching length between the stator and the rotor. Generally, the pressure difference per stage in a screw pump is 0.6 Mpa; the more stages there are, the higher the pressure. However, the pressure relief mechanism of the screw pump also needs to be taken into consideration
If you ask that way, then it refers to a single-screw pump. Strictly speaking, the design pressure is related to the fitting length between the stator and rotor (the compression length), as well as to the degree of sealing between them (volumetric efficiency). For example, the standard stator single-screw compressor from ALLWEILER in Germany achieves a pressure of 6 Bar at one stage and 12 Bar at two stages... whereas its G-type high-efficiency stator single-screw compressor can reach a pressure of 10 Bar at one stage. On a microscopic level, the outlet pressure of a single-screw pump is automatically distributed evenly across each pitch increment. Therefore, the longer the screw is, the lower the load borne by each stage, and its lifespan is naturally longer. But it cannot be simply said that the longer the screw, the higher the pressure. Since stators of different shapes have different volumetric efficiencies, pressure is related not only to the number of stages but also to the stator efficiency.