01 Preparation before startup
In order to ensure the safe operation of the water pump, a comprehensive and careful inspection of the unit should be carried out before starting the water pump, especially for newly installed pumps and pumps that have undergone major repairs. It is important to pay attention to the inspection work so that problems can be identified and dealt with in a timely manner. The main inspection contents are as follows:
1. Check if the rotor of the unit is flexible and lightweight, and if there is any metal friction sound inside the pump. If so, investigate the cause. This inspection is often carried out by turning the coupling of the unit by hand.
2. Check if the lubricating oil in the bearing is normal and if the oil quality is clean.
3. Check if the gate valve on the water outlet pipe opens and closes flexibly.
4. Check if the anchor bolts and other connecting bolts of the water pump motor are loose or detached, and tighten or repair them if necessary.
5. Remove debris from the inlet of the water pump to prevent damage to the impeller if debris is sucked in after startup.
6. Check whether the direction of rotation of the motor and water pump is consistent, and whether the power supply and distribution equipment is fixed properly; Checking the motor direction is an essential task for newly installed or overhauled water pumps.
7. Check whether the control system is normal, whether the instrument displays accurately, and if there is remote control, also check whether the remote monitoring is accurate and effective.
02 Water diversion and start-up
1. Water diversion
According to the working principle of the centrifugal pump mentioned above, it is necessary to introduce water before starting the centrifugal pump. Generally, small centrifugal pumps mostly use the method of water filling and exhaust, and a bottom valve should be installed at the lower end of the suction pipe. The methods of water diversion include using tap water for irrigation, using elevated boxes for irrigation, and using a water pump for irrigation. Most large and medium-sized centrifugal pumps use a water ring vacuum pump to extract air and introduce water. When there is water gushing out of the exhaust pipe during pumping, it means that the suction pipe and pump are filled with water, and the water pump can be started to work.
For self-priming water pumps installed below the level of the suction tank, opening the inlet valve will automatically fill the suction pipe and pump with water.
2. Start up
Centrifugal water pumps are generally started by closing the gate. When starting, the operator and the crew should not be too close. After the pump speed stabilizes, the valves on the vacuum gauge and pressure gauge should be opened immediately. At this time, the reading on the pressure gauge should rise to the idle head at zero flow of the water pump, indicating that the water pump has been pressurized. Gradually open the gate valve on the pressure pipe, and the vacuum gauge reading will gradually increase while the pressure gauge reading will gradually decrease. The ammeter reading on the distribution panel should gradually increase. The start-up work is completed when the gate valve is fully opened.
When the water pump is closed, the operating time should generally not exceed 2-3 minutes; If the time is too long, the water flow inside the pump will generate heat due to continuous circulation, causing damage to some parts of the water pump.
If only a buzzing sound is heard after the motor is closed and it does not rotate, the power should be immediately cut off to check the cause.
If the water pump rotates without producing water, the pump should be stopped immediately to check the cause.
03 Operation and management of centrifugal pumps
1. After each water pump unit is put into operation, the relevant record items on the daily operation report should be filled out in a timely manner. For computer management, the daily operation data of each pump should be input into the computer's storage system.
2. Pay attention to any abnormal sounds and vibrations from the crew. When the water pump is running normally, the unit should be calm and the sound should be continuous and uninterrupted. Abnormal noise and vibration are often precursors to water pump failure, and in such cases, the machine should be stopped immediately for inspection.
3. Pay attention to checking the temperature and oil level of the unit bearings. The temperature rise of bearings should generally not exceed the ambient temperature of 30 ℃~40 ℃, and the maximum should not exceed 75 ℃. When there is no temperature timer, it can also be touched by hand and judged based on experience. If it feels very hot, the machine should be stopped for inspection.
4. The new unit uses ball bearings with lubricating grease, and the first oil change time is after the unit has been running for 80-100 hours. Afterwards, the oil should be changed approximately every 2400 hours (using molybdenum disulfide lubricant can double the time). For bearings lubricated with mechanical oil, the oil should be changed every 240 hours, and the oil level should be kept between the two marks on the dipstick. If it is insufficient, it should be refilled at any time.
5. The normal dripping level of the packing box is generally controlled to be able to drip continuously and not form a continuous line, that is, 20~150 drops per minute. The amount of dripping can be controlled by loosening and tightening the packing cap. Be careful not to press on one side to prevent wear on the shaft sleeve and cover.
6. Regularly check the coupling and the various foot bolts on the unit. If any deviation or looseness is found, it should be corrected and tightened in a timely manner.
7. Pay attention to the changes in the instrument pointer. Under normal operation, the position of the instrument pointer should be basically stable at a certain position. If there is a drastic change or jumping of the instrument pointer, the cause should be immediately identified. For example, if the vacuum gauge reading rises, it may be due to blockage of the suction pipe or a decrease in the water level of the water source; The pressure gauge reading increases, which may be due to the blockage of the pressure water pipe outlet; The pressure gauge reading drops, which may be due to air leakage in the suction pipe and the intake of air, or due to a decrease in speed or blockage of the impeller. For electric motors, attention should be paid to whether the reading on the ammeter exceeds the rated current of the motor. If the current is too high or too low, it should be stopped and checked in a timely manner.
8. If a large pump unit uses water-cooled bearings or motors cooled by circulating oil, the water and oil circuits should be kept unobstructed. If the circulating cooling system malfunctions, the pump should be stopped immediately for maintenance.
9. If the water level of the injection and suction well changes and falls below the minimum design water level, one or two units should be shut down appropriately to avoid cavitation and damage to the impeller. Generally speaking, urban sewage usually receives less water from midnight to 8am, so special attention should be paid.
10. For water pump units without insulation measures, when the water pump is not running in winter, the water should be drained from the threaded pipe plug at the bottom of the water pump to prevent the water pump from freezing and cracking. Even if the water pump is not used for a long time, it should be drained and stored.
04 Parking of centrifugal pump
Before stopping the centrifugal pump, the vacuum gauge and pressure gauge valves should be closed first, and then the gate valve on the pressure pipe should be slowly closed to implement a closed shutdown.
After parking, pay attention to wiping off the water and oil sludge on the surface of the pump and motor. After the water pump is not used for a long time or stopped in winter, the water inside the pump casing should be drained immediately. For some problems that cannot be handled during operation, they should be dealt with promptly after parking.
For pumps with high head, attention should be paid to the potential damage caused by water hammer when stopping the pump. Generally speaking, the impact of water hammer during pump shutdown is already considered in the design of water pump systems. For operators, it is important to ensure the integrity and effectiveness of the water hammer elimination system at all times, in order to effectively minimize the impact of water hammer when the pump is shut down or suddenly stopped due to faults.
