When buying a pump, is it necessary to specify the value required for the net positive suction head?
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When purchasing a pump, it makes no sense to specify a value for the net positive suction head. When the centrifugal pump arrives at the site and is inspected, who will check whether the net positive suction head meets the required standards? Moreover, how can this net positive suction head be measured?
There is the required NPSH for the pump, as well as the NPSH required for the installation. The NPSH required for the installation is something that must be provided, while the required NPSH is a parameter specified by the pump manufacturer.
You can go to the manufacturing plant to witness the tests
When buying a pump, it’s necessary to calculate based on the actual medium and height conditions, right?
It should be that the equipment layout plan and the pipeline layout plan are prepared first before purchasing pumps. By that time, the effective net positive suction head available for the system has already been determined; therefore, it is necessary to specify the required net positive suction head for the pumps when making the purchase. This is especially true in cases where the temperature is high, the fluid is prone to vaporization, the pump is installed at a great height, and the piping ahead of the pump is complex with high pressure losses – in such situations, it’s even more important to specify the requirements regarding net positive suction head when purchasing pumps
Initially, designers should conduct calculations to determine the net positive suction head available for the device; based on these results, a pump should be selected to ensure that cavitation does not occur under the operating conditions of the device. NPSH is an important performance parameter of a pump. As long as requirements are specified, manufacturers generally will not cheat, but from the perspective of a rigorous work attitude, it is advisable to have the test results verified by the manufacturer. A complete set of factory documentation should include test reports.
The process requirements must be specified, and the net positive suction head of the device as well as the required net positive suction head should be indicated in the manufacturer’s data sheet
To check whether the net positive suction head is satisfactory, it is generally done through on-site verification as mentioned in point 3#. This parameter must be specified when purchasing a pump; it is just as essential as parameters such as head and flow rate. Otherwise, the pump purchased may not meet the required standards or may not be usable. There are quite a few factors that affect the net positive suction head, but all of them are controllable – just make sure none are overlooked
Generally, cavitation tests are conducted when the excess amount is within 0.5, and this can be witnessed on-site
The net positive suction head should be calculated in advance; only by meeting the design requirements can the pump model be determined, which is when the decision to purchase a pump is made