May I ask which type of pump requires a lower net positive suction head?
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Which type of pump requires a lower net positive suction head? I need a pump with a flow rate of 50 cubic meters per hour, a head of 18 meters, and the fluid temperature around 90 degrees. The system is of the backflow type, but the feed tank cannot be placed too high; the liquid level must be no more than two meters above the pump inlet. The feed tank is a vacuum evaporator. Because the previous pump suffered from cavitation, the feed tank was placed at a height of 4 meters, and no cavitation occurred. How to keep the liquid level below 2 meters without cavitation, what type of pump should be chosen, and the material should be 304.
Reply to 1# lzj2008888: It is recommended to use a vertical multi-stage tubular belt pump. The impeller is below the ground level, which effectively increases the installation height difference and thus raises the effective net positive suction head. It is recommended to minimize pipe resistance and reduce the number of bends in the piping.
Use a positive displacement pump! It’s possible to draw liquid below the liquid level! As long as you get used to the pump!
This post was last edited by pydch on 2011-5-11 at 15:44. The effective NPSHr is a property of the pump itself, related to factors such as the structure of the impeller; it can be reduced by lowering the rotational speed or by using a double-suction impeller, thereby decreasing the inlet velocity of the impeller and thus reducing NPSHr. Furthermore, the smoother the impeller surface, the more effective it is in reducing NPSHr.
Reply to 1# lzj2008888: It’s definitely better to use a positive displacement pump for this; try using a gear pump or a rotor pump instead.
We have vertical special pumps with self-regulating flow and an NPSHr of < 0.1 m. For inquiries: fei.root@gmail.com Typical application: condensate transfer.
"However, the feed tank cannot be placed too high; the liquid level should be no more than two meters above the pump inlet. The feed tank is part of the negative-pressure evaporator. As you described, the liquid in the feed tank above the pump is in a saturated state, and the effective net positive suction head of the pump depends solely on the height of the liquid column. If the liquid level is 2m from the pump centerline, NPSHa=2m. The centrifugal pump chosen earlier probably had an NPSHr of over 1.5 m, which makes cavitation more likely to occur. It is not easy for domestic pump manufacturers to supply pumps with a low NPSHr of 1.5 m. Foreign companies such as Flowserve and ITT Goulds can do it. There is also a very special type of pump, different from the side channel pump; only a few manufacturers in Germany such as SIHI, SPEC PUMPEN, and SERO are capable of producing it. Its working principle is unique, as it can handle two-phase flow of vapor and liquid, and it can operate successfully under the conditions you mentioned of 2 meters. However, its maximum flow rate is 32 m3/h, and two pumps are required to achieve a flow rate of 50 m3/h.
API VS6 pump, but this pump is a bit expensive!
Suggestion: The pump inlet is equipped with an inducer, and the pump has a double-suction design； The pump should be positioned as low as possible below the horizontal level to improve its resistance to cavitation.