Should the outlet valve be closed when starting a centrifugal pump?
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Should the outlet valve be closed when starting a centrifugal pump? The outlet valve should be closed when starting a centrifugal pump, but it cannot be closed when starting a positive displacement pump. Since there is no fluid in the pump’s outlet pipeline when the centrifugal pump starts, there is no pipeline resistance or head loss. After the pump begins to operate, its head is very low while the flow rate is high; at this point, the motor driving the pump generates a large amount of power (according to the pump’s performance curve), which can easily lead to overload and damage to the pump’s motor and electrical wiring. Therefore, it is necessary to close the outlet valve at the time of startup, and only after the motor reaches its rated speed should the outlet valve be opened so that the pump can operate properly. Generally, positive displacement pumps have self-priming capability. The flow rate of a centrifugal pump changes significantly with pressure, whereas the flow rate of a positive displacement pump changes only slightly with pressure. Contrary to the trend where the shaft power of a centrifugal pump decreases as the head increases, the shaft power of a positive displacement pump increases as pressure rises. This requires that safety valves be installed on the positive displacement pump and within the pumping system, to prevent accidental blockages in the discharge pipeline, which could lead to excessive pump pressure and thus high power consumption, resulting in damage to the prime mover or the pump due to overload. Therefore, when starting a positive displacement pump, the outlet valve cannot be closed; it can operate normally by simply starting it.
Before starting the pump, the inlet and outlet valves of the pump should be in the following open positions: Inlet valve: fully open； Export valve closed, centrifugal pump fully closed, all other pumps fully open (when the mixed-flow pump is used for vacuum priming, the export valve is fully closed).
The inlet valve of the centrifugal pump is open, and the outlet valve is closed. Fully open the inlet and outlet of volume-type pumps
It seems that the way workers operate in factories is a bit different from theory
Is it necessary to operate the minimum flow line of the centrifugal pump during startup in order to prevent cavitation?
When the centrifugal pump starts, the outlet valve should be left slightly open. For pumps with recirculation, such as boiler feed pumps, it may not be necessary to open the main valve, but the recirculation valve must be opened. This prevents the motor from being damaged due to starting under load, and it also avoids pressure buildup in the pump, which could cause leakage in the multi-stage pump’s casing. My opinion is for reference only.
Before starting the centrifugal pump, the outlet valve should be closed, and it should be opened 2–4 minutes after the pump starts running. The purpose is: 1. To start without load and save energy ； 2. Prevent pump suffocation.
Before starting the centrifugal pump, the outlet valve should be closed and the bypass valve opened, to prevent high motor current during startup from causing damage to the motor
The outlet valve should be closed to reduce the starting current.
Turn it off so that the pump can start under no load.