Regarding the parallel operation of centrifugal pumps!
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Assume there are two independent containers, A and B. The pressure in container A is 0.5 MPa, while that in container B is 0.3 MPa. Two identical centrifugal pumps are used to draw the liquid from each container; the inlet pipelines have a diameter of DN65. The outputs of these two pumps are connected through approximately 5 meters of piping to a single DN50 pipeline. The pump pressure for both pumps is 0.8 MPa. Let’s discuss whether there are any issues with this type of process connection ? Can the flow rate of each pump reach the rated discharge volume, that is, the total discharge volume should equal the discharge volume of one pump multiplied by 2, or it should be slightly less than that
1. There is no issue with the process connection, as the outlet pressures are the same; this is a common occurrence. 2. The operating conditions of the two pumps are different; if pump A can achieve its rated flow rate, then pump B will have a lower flow rate due to its higher head compared to pump A. It is recommended that the two pumps should not be of the same type; based on the process requirements, pump B should have a head of 0.5 MPa while pump A should have a head of 0.3 MPa
Whether pumps with the same performance can be used in parallel depends on the following factors: 1. If outlet valves are used to control pressure and flow, pumps with a head of 0.5 MPa can be used in parallel. For the pump serving container A, it is sufficient to adjust the pressure before the valve to 1.0 MPa using the outlet valve, but this results in higher energy consumption； 2. If control via an outlet valve is not desired, then pumps with the same performance cannot be used; as mentioned on the second floor, two pumps with different performances should be used in parallel.
There are no issues with the process connection, and using pumps with the same performance is also fine! What does pump pressure refer to? If it is the pump’s head, then it has no impact! If it refers to the outlet pressure of the pump, then a pump with the same performance cannot be used, as its flow rate varies at different head levels! :)
I have a different view on my sister’s suggestion: she said that pump B has a head of 0.5 MPa and pump A has a head of 0.3 MPa. It doesn’t seem like such units are used for head. If your two pumps are to be connected in parallel, you must use pumps with identical specifications; it is also advisable to have the same outlet pressure for them.
This connection is not allowed. Since the inlet pressures of the two pumps are different while the outlet pressures are the same, this indicates that the work done by the two pumps is not identical; the fluid output by each pump also differs. When they are started simultaneously in parallel operation, one pump will deliver more flow than the other. To ensure proper matching during operation of these two pumps, it is possible to adjust the diameters of their inlets and outlets, or to adjust the valves at the pump outlets. Additionally, it can be adjusted via the outlet valve. The reference indicator is the current when a single pump is operating.
The unit for head is indeed not MPa; it’s always meters. Here, I would like to thank moderator Zhang Yaxiong; it is probably slightly more than 50 meters and 30 meters. Since the inlet pressures of the pumps are different, the head capacity required of the pumps should vary accordingly. Of course, it doesn’t mean that the same type of pump cannot be used; it’s just a recommendation. As BAGE mentioned above, to maintain the same flow rate, it is necessary to adjust the outlet valve. If the inlet and outlet pressures of the two pumps are roughly the same, there is no need to choose pumps with different head capacities. Last edited by sister on 2009-2-3 11:08]
Agreed. . Tests confirmed that pump A can operate at its rated current, while although pump B has the same outlet pressure as pump A, its current is much lower than the rated value; in other words, pump B is essentially doing unnecessary work. .