Houses that depend on the groundwater system, they course require an effective and efficient pumping system and pumping equipment. One of the pumping devices which are mostly used for pumping out water from underground would be a submersible pump.
However, to ensure the satisfactory performance of these submersible pumps, the pump set must be properly selected, installed and maintained. Proper maintenance does not start with rectification repairs or replacement of worn parts but starts right at the time of equipment selection. Equally important is a proper installation. Negligence of fundamental precaution, during installation, may result in premature failure of the equipment. Finally, good operation depends on good maintenance.
1. Selection of pump set:
A proper selection of submersible pump sets ensures trouble-free working for a longer duration. The following criteria have to be considered for selection.
Borewell size:
As submersible pump sets are normally installed on bore wells, the diameter of the bore well is the restricting factor in selecting the size of the pump set. The best size of the borewell is a 6 to 7-inch diameter because the pump can be inserted into the bottom of the ground and fixed easily.
Discharge:
The yield of the bore well is an important criterion for pump selection. For overall efficient performance, the rated discharge of the pump should be taken as 80% of the yield of the bore well. It is desirable to obtain a yield certificate from a bore well contractor. Discharge can be around approximately 0.5 hp is 5 gallons per minute. So you do not need to struggle for calculations just take an approximation from the list provided by the manufacturer and select the amount of water you need to fill your overhead tank. Almost all manufacturers provided the same specification because of standard physical if followed for the design of the submersible pump.
Total Head:
To work out the total Head, add static head, drawn down, seasonal variation in water level and the frictional losses in bends, reducers, non-return valve, column pipe and delivery pipe. This is simply other terms that include the height of the discharge outlet of the pipe because the height is directly proportional to the pressure of the liquid at that particular position, the pressure at which the liquid to pumped out the discharge outlet point is termed as the head of the pump.
Motor H.P number of stages:
From the pump selected above and the desired head, select the number of stages and the corresponding H.P/ phase from the performance chart having maximum efficiency at that duty point.
2. Description of submersible pump set:
The motor and pump are together called a pump set and they are explained individually:
The submersible pump set which is wet type will have a motor of type squirrel cage which can be completely filled with cold, clear water. Motors are suitable for operating in a voltage range of 350 to 440 volts in three phases and 180 to 240 volts in the case of a single-phase power supply. If it contains thrust bearing then it can withstand axial thrust loads with minimal wear and tear. A seal ring and sand guard should be provided to protect the pump from the sand and other foreign particles.
Pump:
Submersible pump sets have a mostly centrifugal multi-stage pump, and there are two types depending on the requirements like for high heads radial flow type of pump is used and for high discharge mixed flow type of centrifugal multi-stage pump is used.
3. Installation of Submersible pump:
Motor filling: The position of the motor should be kept vertical. Mostly a water filling plug is provided at the top of the pump casing so that it can be primed with clean, acid-free water. The water should be oil-free and sand-free before pouring into the plug hole. Gently move the motor to and fro and leave it for 10-15 minutes, with the plug holes open so that any air bubble trapped in the winding will escape. Now pour more water to the loss of volume caused by the escaped air bubbles and screw up the two plugs, the motor is to be checked thoroughly for leakage of water before it is installed. The motor is now ready to be coupled to the pump and installed.
Cable Connection and Megger Test: Connect additional cable length to the standard 3-meter cable supplied with the pump.
The selection of the additional cable must be proper to ensure the proper functioning of the pump. The cable - section/size should match the motor power, line length and starting system. To select the correct cable diameter size we must know the details regarding the nominal voltage of the motor, the nominal power of the motor and the supply cable total length details.
To connect the additional cable to the pump cable, cut off and strip the cable ends so that each lead joints are staggered at regular intervals. The colors of the leads which are to be joined together must be identical.
Insert the bottom plug and plastic tube into the pump cable and the top plastic plug must be inserted into the jointing cable. Join each lead and solder properly. Ensure that after jointing approximately 15 mm of intact sheathing lies within the interior of the cable splicing sleeve on each side. After soldering file off the sharp corners on the soldering joints. insulate each joint separately by winding the rubber taps and adhesive tape tightly to at least 2 inches across the joint.
Push the plastic tube over the joints and ensure that it is central. Cap the bottom plug and push it securely into the bottom of the tube. Wind the Adhesive tape tightly around the bottom end of the tube plug and the pump cable, and press firmly to ensure a perfect seal.
suspend the joint vertically so that the bottom end of the tube points downwards. Heat the tar-based compound in a small tin and pour the molten compound into the tube from the top end. Refill the cavity to overcome any shrinkage and allow the compound to cool. Slide the top plug down the pump cable and push it securely into the topside of the tube. Take the adhesive tape and wind tightly over the top plug and tube.
To check the insulation, conduct a megger test with 500v megger, after keeping the joint in water.
Turn on the power supply and verify the voltage indication at the voltmeter. Check whether all three-phase supply voltage is the same or not. If not, do not start the pump.
The direction of Rotation:
The direction of rotation can be changed by interchanging two phases, Higher discharge shows the correct direction of rotation.
Sand Test:
Care should be taken before installing the pump so that the borewell is well-flushed so that it is free from sand and silt. The pump set is suitable for pumping clear cold water with a maximum permissible sand content of 10 gms per cubic meter. A recently installed bored well, submersible pump is to be started with the gate valve on the discharge line partially opened at the initial condition. The underground water should be examined and tested for the percentage of sand content. Sand content in the water is visible in the glass tube, then the pump set should be run continuously with the gate valve on the discharge line partially opened till the sand content of the water comes to a satisfactory level. A noticing action to be considered is that the pump should not be stopped until we observe clear water, i.e. it should not be turned off during pumping sand-contained water. A high level of sand content will cause a premature tear and wear of the pump's internal parts.
Shut -Down Periods:
The pump set must not be left idle for a week or so since it might cause jamming of moving parts. It should be started at least once every week for five minutes. This will ensure that the pump set is ready for service at any desired time.
Operation at Shut Off:
The pump set must not be run for more than three minutes at zero discharge since the pump will get overheated due to the churning of water in the pump. If the low discharge is required at least 25 percent of the maximum discharge must be allowed.
Switching Frequency:
The stand-still time of the pump between switching off and switching on again should be at least five minutes.
The selection of the additional cable must be proper to ensure the proper functioning of the pump. The cable - section/size should match the motor power, line length and starting system. To select the correct cable diameter size we must know the details regarding the nominal voltage of the motor, the nominal power of the motor and the supply cable total length details.
To connect the additional cable to the pump cable, cut off and strip the cable ends so that each lead joints are staggered at regular intervals. The colors of the leads which are to be joined together must be identical.
Insert the bottom plug and plastic tube into the pump cable and the top plastic plug must be inserted into the jointing cable. Join each lead and solder properly. Ensure that after jointing approximately 15 mm of intact sheathing lies within the interior of the cable splicing sleeve on each side. After soldering file off the sharp corners on the soldering joints. insulate each joint separately by winding the rubber taps and adhesive tape tightly to at least 2 inches across the joint.
Push the plastic tube over the joints and ensure that it is central. Cap the bottom plug and push it securely into the bottom of the tube. Wind the Adhesive tape tightly around the bottom end of the tube plug and the pump cable, and press firmly to ensure a perfect seal.
suspend the joint vertically so that the bottom end of the tube points downwards. Heat the tar-based compound in a small tin and pour the molten compound into the tube from the top end. Refill the cavity to overcome any shrinkage and allow the compound to cool. Slide the top plug down the pump cable and push it securely into the topside of the tube. Take the adhesive tape and wind tightly over the top plug and tube.
To check the insulation, conduct a megger test with 500v megger, after keeping the joint in water.
4. Operation of Submersible Pump:
Turn on the power supply and verify the voltage indication at the voltmeter. Check whether all three-phase supply voltage is the same or not. If not, do not start the pump.
The direction of Rotation:
The direction of rotation can be changed by interchanging two phases, Higher discharge shows the correct direction of rotation.
Sand Test:
Care should be taken before installing the pump so that the borewell is well-flushed so that it is free from sand and silt. The pump set is suitable for pumping clear cold water with a maximum permissible sand content of 10 gms per cubic meter. A recently installed bored well, submersible pump is to be started with the gate valve on the discharge line partially opened at the initial condition. The underground water should be examined and tested for the percentage of sand content. Sand content in the water is visible in the glass tube, then the pump set should be run continuously with the gate valve on the discharge line partially opened till the sand content of the water comes to a satisfactory level. A noticing action to be considered is that the pump should not be stopped until we observe clear water, i.e. it should not be turned off during pumping sand-contained water. A high level of sand content will cause a premature tear and wear of the pump's internal parts.
Shut -Down Periods:
The pump set must not be left idle for a week or so since it might cause jamming of moving parts. It should be started at least once every week for five minutes. This will ensure that the pump set is ready for service at any desired time.
Operation at Shut Off:
The pump set must not be run for more than three minutes at zero discharge since the pump will get overheated due to the churning of water in the pump. If the low discharge is required at least 25 percent of the maximum discharge must be allowed.
Switching Frequency:
The stand-still time of the pump between switching off and switching on again should be at least five minutes.
5. Troubleshooting submersible pump problems:
- For every operation, I have to pour water into the pipe to start the motor to pump water from the underground bore well to the overhead tank.
- Failure of NRV (non-return value or check value) on the discharge line of the pump. Check if solid particles are stuck in it, and clean it if possible if not replace the value. It helps to hold the water in the pump casing and suction line after the pump is switched off. This prevents the pump from becoming empty for the next operation. So no need to fill the water again and again.
- Maybe the water level in the ground is dropped down and so the suction lift is not possible by the pump. Airlocks will be created in the suction, they are removed when we pour water
- Which type of discharge pipe is suitable for the submersible pump to discharge water from a bore well.
- Usually, GI pipe is used as a discharge pipe, however, this pipe corrodes quickly due to the water and moisture in the well.
- HDPE pipe is corrosion-resistant to the bore well environment and can withstand underground temperatures. However, if there is a need to remove the motor and pump out of the bore well for maintenance there is a chance of jamming. HDPE pipe may stretch by the applied pressure during pull-out and deform its size and shape.