(a) Shaft seal inspection:
For the packing seal pump, it is necessary to check the sealing water used, and ensure that the amount of the sealing water is sufficient and its pressure is normal.
For the slurry pump, the pressure of the sealing water should be 0.05 Mpa higher than the pump's outlet pressure. Adjust the packing gland to obtain a small stream of water along the shaft. Note that for pumps directly supplied by the slurry manufacturing plant, the packing gland is tightened more tightly to reduce the vibration of the shaft during transportation.
For the centrifugal sealed impeller pump, unscrew the grease seal cover a few turns to allow the seal chamber to be filled with oil.
The rubber-lined pump is equipped with a rubber pressure-reducing cover. This type of pump is usually sealed with a lip-type rubber ring and does not require grease.
(b) Loosening the shaft:
To prevent shaft vibration and damage during transportation, the bearings of the slurry pump must be tightened. Usually, a wrench (one of the assembly tools) is used to tightly screw the positioning screws onto the bracket to secure the bearings.
Before starting the pump, the positioning screws must be removed to allow the bearings to return to their free state. Then, use a wrench to turn the shaft clockwise to see if the shaft can rotate the impeller smoothly. If any abnormal noise occurs, it should be eliminated by adjusting the impeller clearance (refer to Pump Assembly: Impeller Clearance Adjustment).
(c) Check of motor rotation direction:
Remove all the V-shaped belts or the entire coupling. It is particularly important to note that if the rotation direction is opposite to the direction indicated by the arrow on the pump, the impeller will come loose and fall off the shaft, causing damage to the pump.
Start the motor and check its rotation direction. If it is incorrect, correct it. Make sure the pump shaft rotates in the direction indicated by the arrow on the pump body.
Reinstall the V-belt or coupling, ensuring that the shaft is centered after tightening the belt.
(d) Startup of the pump:
Check to ensure that all the belts are tightened properly, that the impeller can move freely, and that the shaft seal is functioning correctly. If using shaft seal water, check whether the pressure is correct.
The experiment shows that whenever possible, water should be used to start the pump before pumping the slurry, and before stopping the pump, the pump should be kept running for a while.
Open the valve of the suction pipeline (if such a valve exists), and check whether there is any blockage at the pump inlet. Start the pump and the motor and make them reach the normal speed. If the pump is operating under the suction condition, then use the provided device to follow the water intake procedure.
After the pump starts drawing water, if there is a water isolation device (if such a device is present), check the pressure at the suction and discharge ports (if pressure gauges have been installed at both locations).
The flow rate can be measured by a flowmeter, or it can be estimated by observing the outlet.
Check the leakage at the packing area. If the leakage is not significant and the packing cover is slightly warm, then loosen the packing cover nut. If this does not work and the cover continues to heat up, stop the pump to allow the cover to cool down. The packing cover nut should be loosened to the extent that the packing behind the cover can move freely.
Note:
Even though the leaked water from the filler is slightly warmer than the water supplied to the filler, this is still within the normal range because the leaked water will carry away the heat generated by the friction within the filler.
During low-pressure (single-stage) operation, a very small amount of leakage is required. This is because the low-pressure pump can operate with a small amount of water leaking through the packing. When the packing gets hot, it does not need to be stopped immediately. The pump will only be stopped if there is hot steam or smoke coming out.
The annotations on the reference page are about the assembly of the pump.
The problem of packing overheating usually occurs only during the initial start-up of the pump. That is, when the pump is first started and the packing gets hot, the common approach is to start - stop - cool. The pump is started 2-3 times until the packing and the shaft sleeve have achieved a good running-in.
A better method to solve the problem of packing overheating is to allow the leakage to exceed the rated value when starting the pump. After the pump has been running for 8 to 10 hours, the packing leakage can be adjusted to the ideal value using the gland bolts.
If the packing always gets hot, it should be replaced.
When the outlet pressure is below 0.5 Mpa, use buttered cotton rope packing or oil-soaked asbestos packing. When the pressure is above 0.5 Mpa, use polytetrafluoroethylene packing or carbon fiber impregnated polytetrafluoroethylene packing. For pressures exceeding 1 Mpa, it is usually necessary to install packing rings between the gland and the nearest layer of packing.
(e) Abnormal startup
If the pump fails to draw water, it may be caused by one or more of the following reasons.
(1) Inflation of the inhalation tube
After the pump has been running for some time, it is likely that due to drawing water from the pit, the slurry will settle in the suction pipe or around it, thereby preventing water from entering the impeller. Therefore, the water level in the pump can be checked using the pressure gauge at the pump's suction inlet.
(2) The air enters the pump through the packing.
Any one of the following working conditions can cause air to pass through the packing and enter the pump. When air enters the pump, it often prevents the pump from drawing water or causes the water supply to be interrupted during operation.
1) The sealing water pressure is too low;
2) Excessive wear of the filler;
3) The water for the packing seal gets blocked in the piping of the packing box.
If such a fault occurs, it can be detected in advance through the inspection of the packing. Then, a remedy will be available.
(f) Operational failure
Ⅰ) ) Inlet pipe blockage
It is likely that during the operation of the pump, impurities are drawn to the bottom of the suction pipe, causing local blockage. This blockage does not cause a pump shutdown failure, but it can reduce the pump's flow rate. It can also cause the outlet pressure to continue to decrease, increase the suction vacuum degree, or due to the excessively high suction vacuum degree, cavitation may occur inside the pump, causing the pump to be in an abnormal operation and vibration state.
2). Impeller blockage
The impeller allows a certain particle size of materials to pass through. If materials with excessively large particle sizes enter the suction pipeline, it may cause blockage at the inlet of the impeller, thereby limiting the pump's discharge volume. Such a fault often leads to a decrease in power, as well as a reduction in the outlet pressure and suction vacuum degree.
The vibration of the pump may also be caused by the imbalance of the impeller.
III) Blockage of the outlet pipeline
When large particles are highly concentrated in the discharge pipe of the pump, the discharge pipe will become clogged. Or if the speed of the discharge pipe is too low to adequately convey the liquid, such clogging will manifest as an increase in the outlet pressure and a decrease in the motor power.
