How Your Well Works

Part II - The Pump

Jet Pumps

By far the most common type of pump is the jet pump. This popularity is mostly due to the extremely simple operation and ease of replacement that jet pumps enjoy. Their greatest limitation however is that their ability to pump water tops out at around 25', relegating their use to shallow wells or ponds. They operate through a combination of centrifugal force and changes in atmospheric pressure to draw water, therefore there must always be water in the pump and in the suction lines to draw water from the well. In order to ensure that there is always water in the pump, a 1-way check valve (also known as a foot valve) is installed at the end of the suction line. As the motor spins the impeller, centrifugal forces push the water from the impeller into a narrow nozzle called a venturi. The unique shape of the venturi constricts at one end causing the flow of water to constrict while at the same time increasing pressure. This high velocity liquid passes over a small port in the top of the nozzle, creating a vacuum at that point. The other side of the venturi expands again, decreasing the velocity and increasing the flow of water. The vacuum created by the high velocity water also serves to pull more water in than was originally injected into the venturi. This effect is what allows the jet pump to pull water from the well and also allows it to create pressure to push the water into the rest of the system.

By placing the venturi inside the well rather than inside the pump body, a jet pump can be used to pull water from a greater depth. (up to about 75') In this setup, two pipes are connected to the pump. One is connected to the output side of the impeller, forcing water down into the well and into the jet ejector assembly. If you look inside this ejector assembly, you'll see the same nozzle and venturi setup as you would find on the shallow well jet pump. As water is forced through the jet ejector, a vacuum is created just like with a shallow well pump. This vacuum allows standing water from the well to be pulled in and forced out through the output side of the ejector which is connected to the second pipe. This water is then carried by the pressure from the impeller back up to the pump and out into the rest of the water system.

Submersible Pumps

Submersible pumps are the second most common pump used for household water systems. As the name suggests are completely submerged in well water. This type of pump can be used at depths ranging from less than 20 feet to several hundred feet and provide anywhere from 5 gallons per minute to several hundred gallons per minute. They operate using a series of impellers stacked in stages on top of each other. Because the pump is submerged, water enters freely through a screen placed between the pump body and motor without needing to be drawn in. As the impellers rotate they fling the water upwards towards the diffuser which channels the water into the next impeller. With each stage the water passes through, the water's velocity is increased until it reaches the last stage where it is ejected from the pump through the discharge pipe and into the water system. The deeper the well, the larger the pump required to push the water out of the well. In the case of a submersible pump, larger simply means more staged impellers and a higher horsepower motor to operate them.

The discharge end of the pump is connected to the rest of the system using special thick-walled pipe called drop pipe. This pipe is connected together in 20' sections running from the top of the well to the depth at which the pump will eventually sit. At one time galvanized steel pipe was the pipe of choice for this application, however with the high availability and the fact that it is corrosion-proof, PVC has mostly replaced galvanized in all new installations.

Modern installations like the one pictured keep the water line underground through the use of a pitless adaptor. A pitless adaptor is simply a special flange which connects to a hole cut in the side of the well casing. Two rubber o-rings create a seal between the casing and the adaptor preventing water from leaking out and contaminants from entering the well. This has the added benefit of a clean professional appearance as well as being tamper-resistant. In older installations, pipe and wire are brought through the top of the well seal and over the side of the wellhead and are then buried to prevent damage and freezing. This creates a situation where the exposed portion of pipe can possibly freeze and break. It is also subject to tampering and damage by vehicles running over the wellhead.

The power for the pump is provided by heavy gauge wire (usually 10 gauge or less) with a special waterproof coating. This wire is connected to the leads on the pump's motor using a special waterproof heat-shrink kit. The wire travels out of the well, underground and into a control box mounted on the wall of your pumphouse or garage.

If you were to look inside of a typical modern pump control box, you would see two sets of red and black wires and a yellow wire connected to a bus at the bottom of the box. You would also see a small blue rectangular box and a large black cylinder. Large high-torque AC motors such as the one found in your pump require the use of a control box to energize and discharge the start winding which gets your motor spinning. This winding is connected to the red wire coming from the well to the control box. When power is applied to the control box, this starts a series of events which eventually start your pump motor. Firstly, the relay (the blue rectangle) is in the ON position and energizes the capacitor (the black cylinder) by connecting the power wire L1 (red wire) to the capacitor (orange wire). The capacitor then connects to the motor start winding (red wire to pump). When the motor is at about 2/3 of full speed, changes in current draw cause the relay to switch OFF disconnecting power from the capacitor and the motor start winding. In the OFF position, L1 is connected to the run winding (black wire to pump). The yellow wire to the pump is known as the common wire, it connects to both the start winding (red wire to pump) and the run winding (black wire to pump). It is always connected to power L2 (black wire). Just like a battery, this capacitor gets warm to the touch when charged. Repeated charging and discharging of the capacitor, such as would be caused by rapid cycling of the pump, can cause it to swell and leak the electrolyte solution used to store it's charge. This is the single most common cause of pump failure and the easiest to remedy. Simply replace the capacitor with one of equal size and the pump will start working again.

When it's finally time to replace the pump, it must be pulled from the well. Your pump contractor first removes the well seal and attaches the cable from a pump hoist to the drop pipe. A pump hoist is almost more of a miniature crane mounted to the body of a service truck. It is designed to pull a pump from even hundreds of feet down in a well. Once the cable is attached the drop pipe is disconnected from the pitless adaptor and the pump, pipe and wire are pulled out of the well to be repaired or replaced. Fortunately, submersible pumps and motors are designed to run for many thousands of hours before this kind of work needs to be performed.