Precautions for starting and stopping centrifugal pumps

Closing the outlet valve before starting the pump is intended to reduce the current during startup, while closing it before stopping the pump prevents backflow of fluid in the outlet pipeline from potentially damaging the impeller. Additionally, attention must be paid to venting air when starting a centrifugal pump.

Preparations before starting 　　1. Turn the motor blades by hand; the impeller should rotate smoothly without any jamming. 　　2. Open the inlet valve and the exhaust valve to fill the entire pump chamber with liquid, then close the exhaust valve. 　　3. Turn the pump by hand to allow the lubricant to reach the mechanical seal faces. 　　4. Turn on the motor to confirm whether the direction is correct. 　　2. Starting and Operation 　　1. Fully open the inlet valve and close the outlet line valve. 　　2. Connect the power supply; once the pump reaches its normal operating speed, gradually open the valve on the discharge pipeline and adjust it to the desired operating conditions. 　　3. Pay attention to the instrument readings and check for leaks in the shaft seals; under normal conditions, the mechanical seal should leak at a rate of less than 3 drops per minute. Check that the temperature rise at the motor and bearings is ≤ 70 degrees C. If any abnormalities are detected, they must be addressed promptly. 　　Three stops 　　1. Gradually close the valve on the discharge pipeline and cut off the power supply. 　　2. Close the inlet valve. 　　3. If the ambient temperature is below 0°C, the liquid inside the pump should be drained to prevent it from freezing and cracking. 4. If it is to be out of use for an extended period, the pump should be disassembled, cleaned, and stored in packaging.

Reply to 2# chinazwr: May I ask why it is necessary to vent air before starting a centrifugal pump? How is the exhaust handled? Thank you!

After the medium is filled into the centrifugal pump, the air is expelled. After the centrifugal pump starts, the fluid inside the pump is forced out through the outlet by centrifugal force, creating a negative pressure at the center of the pump. This negative pressure draws in fluid at the inlet, allowing the pump to continuously discharge and draw in fluid. Otherwise, there is air inside the centrifugal pump; air has a low mass (it is light), so it cannot generate sufficient centrifugal force. As a result, the medium cannot be discharged from the outlet, nor can the medium at the inlet be drawn in. When venting, slightly open the outlet vent valve; once medium is detected, close the vent valve promptly. Of course, hazardous media such as toxic substances must not be discharged arbitrarily.

From my experience, before starting a centrifugal pump, it is necessary to fully open the pump’s inlet and slightly open the outlet valve. This helps to remove gases from within the pump, and it also prevents damage to the pump’s components caused by excessive heat – as no flow at the outlet means that the heat generated cannot be dissipated. Of course, to stop the pump, one first closes the outlet valve and then stops the pump. Generally speaking, if the pump outlet valve is slightly open, the chances of successful pump startup are quite high, and it is basically unaffected by gas. Personal experience, for reference only.

Mainly, the power is at its minimum when the outlet current is 0, and thus the starting current is also at its minimum! Protect the motor

Our company has set a minimum flow threshold for shutdown, so the outlet valve cannot be closed. The circulating water pump I purchased has a ball valve on its pump casing; each time the pump is started, it is necessary to ensure that the inlet valve is open and to use the ball valve to release air.

Both when starting up and stopping the equipment, it is necessary to close the shut-off valve first. Closing it before starting up prevents excessive current spikes, as well as air entrapment. Closing the shut-off valve when stopping the equipment prevents fluid from flowing back, which could cause damage to the housing and impeller and thus extends the equipment’s service life.

Reply to 6# slayerstar: There is a problem with your view. Firstly, when the centrifugal pump discharges air, this can be done through a backflow valve. When starting the pump, if the outlet valve is open, the current drawn by the centrifuge increases suddenly upon startup; this not only damages the pump’s impeller but also causes severe wear on the pipes. However, if the outlet valve is closed, the centrifugal pump will not do any work, and the motor’s startup will not be affected

Reply to 10# gsh1037221014: What I said just now was to slightly open the outlet valve; it shouldn’t cause that much damage to the pump, right?