What should the inlet and outlet valves be in when starting and stopping a centrifugal pump?

I see everyone say to open the inlet valve at startup to fill the water pump, but won’t the water filled in flow out through the inlet? Is this the exit? At startup, the inlet valve opens and the outlet valve is slightly open. When pumping, the inlet valve remains unchanged while the outlet valve closes.

The water pump is installed on the ground at a certain height. End-suction centrifugal pumps have water intake at the bottom and discharge at the top; when water is injected through the inlet, doesn’t it flow out through the outlet as well? Why open the imported valves again?

Water injection is carried out through the inlet valve, with water being forced in by pressure or potential energy

I see there’s also a water injection port on the pump casing – isn’t it used for injecting water?

The liquid level in the tank in front of the water pump is generally higher than that of the pump; if it is lower, there should be a check valve at the pump inlet.

For centrifugal pumps, water must be filled into the pump before starting up. The purpose of this is to prevent the pump from suffering from \"air locking\"; the water injected does away with the air in the pump chamber, a process also known as priming the pump. A check valve is installed on the inlet side of the pump, so the water used to fill it does not flow out completely from the pump body. Before starting the pump, open the inlet valve first and slightly open the outlet valve; once the pump is running properly, adjust the outlet valve to the appropriate setting ； To stop the pump, first slowly close the outlet valve, and then turn off the motor.

The poster isn’t asking about ordinary centrifugal pumps, but rather self-priming pumps used to draw water from a pool. This type of water pump has a solenoid valve at its inlet that acts as a check valve; water from the tank can be drawn into the pump chamber but cannot flow back into the tank ； Before starting the pump, there is a dedicated water filling line used to fill the pump; once this is completed, the pump is started following the standard startup procedures for centrifugal pumps. The following is excerpted from BD: After the pump starts properly, the impeller draws in both the liquid present in the suction chamber and the air in the suction pipeline, mixing them thoroughly within the impeller. Under the effect of centrifugal force, the liquid carrying the gas flows toward the outer edge of the volute, resulting in the formation of a white foam band of a certain thickness as well as a high-speed rotating liquid ring at the outer edge of the impeller. The gas-liquid mixture enters the gas-liquid separation chamber through a diffusion tube. At this point, due to the sudden decrease in flow rate, the lighter gases are separated from the gas-liquid mixture, and the gases continue to rise and be discharged through the pump’s outlet. The degassed liquid returns to the liquid storage chamber, and then enters the impeller through the return hole, where it mixes again with the gas drawn in from the intake pipeline inside the impeller. Under the action of the rapidly rotating impeller, it flows toward the outer edge of the impeller... As this process repeats itself, the air in the suction line gradually decreases until all the gas is drawn in, completing the self-priming process; at that point, the pump begins to operate normally.

Original poster, you mentioned two scenarios: 1. If it is an industrial centrifugal pump, then the fluid entering the pump from the front must flow in from above, so the water used to fill the pump will not flow away. 2. There is another type of pump in which the inlet pipeline enters the pump’s inlet from below; this is a self-priming pump. It may seem as though water will flow out when filling the pump, but there is a check valve in front of the pump’s inlet, preventing backflow.

Actually, there is a bottom valve at the bottom of the pump. It’s simple if you understand pump operation; if not, come to this forum to learn – then it becomes even simpler to consider

There is a bottom valve at the inlet side, similar to a check valve that prevents leakage