Essential Series on Pump Selection and Piping(4)

                                        Essential Series on Pump Selection and Piping(4)

5. Influence of Flow Rate and Head

Flow rate determination

A. If the minimum, normal, and maximum flow rates are specified in the production process, the maximum flow rate should be considered.

B. If the production process only specifies the normal flow rate, a certain margin should be considered.

For the high-flow, low-head pump with NS100, the flow margin should be 5%. For the low-flow, high-head pump with NS50, the flow margin should be 10%. For pumps with NS between 50 and 100, the flow margin should also be 5%. For pumps with poor quality or harsh operating conditions, the flow margin should be set at 10%.

C. If the basic data only provides weight flow rate, it should be converted to volumetric flow rate.

6. The Influence of Temperature

The transportation of high-temperature media imposes higher demands on the structure, materials, and auxiliary systems of pumps. Below are discussions on the cooling requirements for different temperature variations and the applicable pump types of the company

1. For media with temperatures below 120°C, a dedicated cooling system is typically not required, and the medium itself is often used for lubrication and cooling. For example, chemical pumps and shielded chemical pumps (the protection class of the motor should be H-grade when exceeding 90°C); while standard and IH chemical pumps, due to their suspension structure, can achieve a temperature limit of 140°C to 160°C; IHF lined fluorine pumps can operate at temperatures up to 200°C; only CQB standard magnetic pumps have a maximum operating temperature not exceeding 100°C. It is worth noting that for media prone to crystallization or containing particles, a flushing pipeline for the sealing surface should be provided (interfaces are reserved in the design).

For media with temperatures above 120°C but below 300°C, a cooling cavity is typically required on the pump cover, and the sealing chamber should also be connected to cooling liquid (requiring a double mechanical seal). When it is not permissible for cooling liquid to mix with the media, the media should be cooled before being connected (which can be achieved using a simple heat exchanger).

3. For high-temperature media above 300°C, not only the pump head but also the suspension bearing chamber should be equipped with a cooling system. The pump structure is typically a central support type, and the mechanical seal is preferably a metal bellows type, though it is costly (prices are more than ten times those of standard mechanical seals).