Centrifugal water pump equipment operation and maintenance

Why should the centrifugal pump be primed before the first start?

If the centrifugal pump is not primed before it is started, there may be gas in the pump. Due to the low weight of the gas, the suction pressure and discharge pressure of the pump are very low, the gas is not easy to discharge, and the liquid cannot be sucked into the pump. Therefore, the centrifugal pump must be primed before it is started, so that the pump is full of liquid to avoid "cavitation" and vacuum.

Why should the standby centrifugal pump be cranked regularly?

① The pump shaft is equipped with accessories such as impellers, which will bend the shaft under the long-term action of gravity. Frequent cranking and constantly changing the force direction of the shaft can minimize the bending deformation of the shaft. ② Check the tightness of the moving parts to avoid rusting of the moving parts due to long-term static, so that the pump can be in standby state at any time. ③ The cranking brings lubricating oil to all parts of the bearing to prevent the bearing from rusting, and because the bearing is initially lubricated, it can be started immediately in an emergency.

Why should the standby hot oil centrifugal pump be preheated before starting?

If the standby hot oil pump is not preheated before starting, during emergency start, hot oil will quickly pour into the cold pump cylinder, which will cause uneven heating of the parts in the pump and bend the main shaft, and cause the stationary ring in the pump body and the impeller seal ring on the rotor to get stuck, causing wear, shaft sticking, shaft breakage and other accidents. In addition, if the oil with high viscosity is not preheated, the oil will condense in the pump tank, and it will not be able to increase the amount after starting, and it may even cause the motor to trip. The same reason for uneven thermal expansion will cause leakage, such as serious leakage at the end face sealing pump cover, balance pipe joint, pump inlet and outlet line flange, packing, etc., and may also cause fire accidents.

What problems should be paid attention to when preheating the standby centrifugal pump?

① The preheating process is correct. Generally, it is the pump outlet pipeline-through the preheating jumper across the inlet and outlet-preheating valve-pump body-pump inlet. Do not open the preheating valve too much to prevent the pump from reversing.

② Preheating is carried out at a speed of 50℃/hour. In an emergency, measures can be taken to speed up the preheating speed (such as blowing the pump body with steam to help preheat). But too fast speed will cause the pump body to heat up rapidly, causing leakage at each joint and the rotor to bend and get stuck.

③ During preheating, the pump should be cranked, usually once every 30-45 minutes, to avoid bending of the main shaft and facilitate the removal of gas in the pump.

④ The cooling water of the bearing box, pump seat, and end face seal should all be opened to protect the shaft and bearings.

Why is a check valve installed at the outlet of a centrifugal pump? What are the types of check valves?

The check valve is installed on the pump outlet pipeline to prevent the liquid from returning to the pump and preventing the pump from reversing. There are two types of check valves: one is a lifting check valve, which is suitable for horizontal installation on the pipeline; the other is a swing check valve, which can be installed on horizontal, vertical, and inclined pipelines. If installed on a vertical pipeline, the medium flow direction should be from bottom to top. Will the motor be burned out if the centrifugal pump is running when the outlet valve is closed?

Whether the centrifugal pump will cause the motor to burn out due to overload when running under the condition that the outlet gate valve is closed is related to the pump's specific speed, flow rate, power curve shape, and the selected motor. Generally speaking, the specific speed of a centrifugal pump is less than 300, and the power consumed by the pump is the smallest at zero flow. As the flow increases, the power consumed also increases. In addition, the motor used for the centrifugal pump is selected based on the design point power, leaving a considerable margin. Therefore, generally speaking, when the centrifugal pump is running under the condition of closing the outlet valve, most of the power is converted into heat energy, causing the temperature of the liquid in the pump to rise and gasify, which will cause damage to the centrifugal pump. Therefore, the centrifugal pump cannot be operated continuously for a long time under the condition of closing the outlet valve.

Why does the centrifugal pump have to close the outlet valve to start?

From the characteristic curve drawing of the centrifugal pump, we have learned that the centrifugal pump has the smallest power consumption when its flow is zero, and the motor rises from the original static state to the working speed. The current at startup (that is, the power consumption of the motor) is 5-7 times greater than that during normal operation. In this case, if the outlet valve is not closed and the mechanical load is increased, it may cause accidents such as motor tripping. In order to start the motor under the minimum load, the outlet valve must be closed.

How to refuel the white oil tank of the high-temperature oil centrifugal pump of the constant pressure reduction device?

When the DCS sealing oil level alarm sounds or the level is slightly lower than the red line below the glass plate, the sealing oil tank must be refilled. The specific operation steps are as follows:

① Operation pump: Open the oil filling valve at the bottom of the manual refilling device, shake the refilling handle, stop when the liquid level exceeds the lower red line of the oil tank, and close the refilling valve.

② Standby pump: Close the nitrogen charging valve, unscrew the oil filling port cover, slowly open the lower valve of the oil filling port, remove the pressure in the tank, and then refill the tank from the oil filling port. Stop when the liquid level exceeds the lower red line of the oil tank, close the oil filling valve, screw on the cover, and open the nitrogen charging valve.