Boreholes are holes that are drilled into the earth’s crust in order to obtain water. Boreholes vary in depth and water yield. Once a borehole is drilled, a water yield test is carried out by placing a test pump into the hole and operating this pump for a period of 4 to 5 hours. This process assists us in obtaining the accurate yield of the borehole. Since all boreholes are different, the selection of a borehole pump depends on the following:
- Depth of the borehole – assists in selecting the pressure capacity of the pump.
- Water yield of the borehole – assists in selecting the water flow of the pump.
- Availability and type of electrical power (three phase or single phase) – assists in selecting the motor power.
Application of borehole – what it will be used for.
Once the correct pump is selected, it is installed inside the hole and is used to supply water to irrigation systems, small and large holdings, businesses, factories, in fact for any operation that requires water.
A borehole pump is made up of a motor and wet end. The motor requires electricity in order to operate/spin thereby rotating a set of impellors in the wet end. This rotating motion propels water from the bottom of the hole to the top. The number of impellors in the wet end determines the volume and pressure of the water that is propelled from the borehole and further determines the motor size in kilowatts.
INSTALLATION OF BOREHOLE PUMPS:
- Once the correct wet end and motor have been selected, they are attached together with nuts and bolts.
- A waterproof joint kit is used to join the motor lead out cable to the submersible cable. The length of submersible cable is determined by how deep the hole is. This cable is specifically designed to be installed under water.
- A Wellzarc filter (designed and manufactured by the Pump & Irrigation Centre) is installed onto the borehole pump using a heat shrink unit. This filter prevents borehole debris from entering and damaging the wet end and also serves as a cooling sleeve.
- High density piping class 12 or 16 together with plasson and galvanized fittings is used to connect the pump from the bottom of the hole to the top. The piping must be heavy duty as it not only used to convey water but serves as a support for the pump.
- A nylon rope is also attached to the pump to serves as a back up support.
- At the top of the hole a galvanized base plate is installed onto the piping and rests on the galvanized sleeve of the borehole.
- A control valve is installed onto the supply piping to prevent the pump from operating beyond its optimum operation rating.
- Armoured cabling is used to supply power from the control box to the motor. A weather proof box is used to connect the armoured cable to the submersible cabling.
A cast iron manhole cover or heavy duty plastic enclosure is used to cover the borehole components at the top of the hole.
If the water yield of a borehole is high, the pump can supply water for a specific requirement directly.If the water yield of a borehole is low, the pump will supply water to a storage tank which serves as a reservoir or a booster of pressure pump will be used to supply the water from the tank to meet the specific requirement.
AUTOMATION UNITS FOR BOREHOLE AND BOOSTER PUMPS:
- When a borehole pump is used to fill a storage tank -LEVEL DETECTOR SWITCHES (float switch with relay or probes with liquid level relay) are used to automatically switch the borehole on when the water level in the tank drops and switch the pump off when the tank is full. The level detector switches are also used to prevent the booster pump from operating when there is no water in the tank.
- A pressure vessel and pressure switch (PRESSURE SYSTEM) is used to automate either a booster or borehole pump. The pressure vessel has a bladder inside it – air is filled between the inner part of the pressure vessel and the outer part of the bladder (air pressure should be atleast 2 – 3 bars) via an air valve. When water enters the inner part of the bladder via the pump – pressure is created between the air and water which in turn is exerted onto the pressure switch (set to a specific cut in and cut out pressure points) – this is responsible for switching the pump off when no water is required and on when water is required i.e. when no water is required the pressure inside the vessel increases until it reach the cut out pressure point thereby switching the pump off and when water is required, the water is released from the vessel decreasing the pressure to reach to the cut in pressure point engaging the pressure switch which then energizes the pump.
- A WATER SENSOR CONTROL UNIT which is similar to a pressure system except no air or pressure switch is required – the unit has a built in sensor that detects when water is required thereby switching the pump on and when no water is required, it automatically switches the pump off.
The pressure system and water sensor control unit are used in conjunction with a pump that is supplying water to homes, garden tap and manual irrigation systems. If a pump is supplying water to an automatic irrigation system only, the automatic operation of the pump can be controlled via the timer i.e. when the timer is engaged to start the irrigation process; it automatically energizes the pump via the pump starter unit that is situated in the timer.