The first of the reasons for the increase in resistance:
the diameter and flow rate of the pump inlet and outlet pipes. Under normal circumstances, if multiple pumps are connected in parallel, and the branch pipe section of each pump is not long, the inlet pipe section can be the same diameter as the pump inlet. The outlet pipe section should be the same diameter as the inlet pipe section. Generally, the diameter of the pump outlet is smaller than the diameter of the inlet, so the number one should be enlarged. The pipe diameters of the inlet and outlet sections of the pump are configured according to the diameter of the pump. Check according to the rated flow of the pump: the diameter of the inlet pipe section is DN300mm and the flow rate is 3.51m/s. The outlet diameter is smaller than the inlet diameter, which is DN250mm and the flow rate is 5m/s. (Obviously not feasible) The pipe diameter of the inlet and outlet sections of the pump is too small, which will inevitably cause a large pressure loss. When configuring a component with a large resistance (such as a pipe filter and a check valve) on each pump branch, pay more attention to the pipe diameter and flow rate.
The second reason for the increase in resistance:
the pipeline filter should use the decontamination device as much as possible, avoiding the use of the pipeline filter, and the operation failure caused by the excessive resistance of the filter may occur. Although the decontamination device has a ζ = 4 to 6, the pipe filter has a ζ = 1.5 to 3 (these data are not accurate and should be related to the diameter of the filter and the number of meshes). However, the decontamination device is conditioned on the main pipe and can be arranged in parallel.
The third reason for the increase in resistance:
check valve
There are many types of check valves, and the resistance characteristics should be specifically understood when selecting. In particular, some so-called "slow-closed noise-reducing check valves" have great resistance. Operational failures caused by excessive resistance also occur from time to time. The head of the circulating water pump of the heating and air conditioning water system is generally not more than 50m. The pressure difference between the inlet and outlet of the pump will not form a serious water hammer, and it is not necessary to select a check valve with complicated functions but great resistance. Resistance characteristics data should be obtained for any component that is placed on an air conditioning or heating system. The dimensionless local resistance coefficient, the flow coefficient KVS or the resistance value at the rated flow.
