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Pump Relay

The pump relay aids in the operation of submersible water pumps with higher-horsepower electric motors. Contained inside the gray metal box is an electrical relay, a motor start capacitor and in some instances a motor running capacitor. The electrical schematic diagram is generally fixed to the inside of the removable cover.

The electrical relay controls the operation of the pump motor and engages the motor start capacitor. The motor start capacitor gives the electric motor an energized boost of power when starting under a load condition. Most submersible pumps, when below a 100 foot depth, require a motor start capacitor because of the large column of water above the pump's outlet fitting. Indication of a bad start capacitor is hearing a humming noise come from the relay box and no water pressure is being built in the pressure tank.

The run capacitor aids the pump motor during its running operation. Many times, pumps greater than 250 feet require a motor run capacitor to balance the voltage load due to the long wire length. Indication of a bad motor run capacitor is a lost of performance in the submersible pumps capacity in recovering the pressure tank. In other words, if the pressure tank usually took 20 seconds to re-fill after being drawn, a bad run capacitor will cause a longer run-time of the pump motor. Increased recover times that exceeds 30 to 45 seconds may be a cause for electrical capacitor testing.

Testing the capacitor whether it is the start or run unit is a straightforward process that can be done with a volt-ohmmeter, needle nose pliers and an insulated handle screwdriver. Shut off the electrical power to the pump. Open the cover of the pump relay box. Pull the wire connections to the capacitor terminals with the jaws of the needle nose pliers. Make a note as to which color wires connect to which capacitor terminals.

If the capacitor is bulging or leaking fluid it is bad, and needs to be properly disposed. Do not get the fluid on your hands as the oil may be toxic.

Remove the capacitor from the relay box and set it on a flat surface. Touch the metal end of the insulated screwdriver to the two electrical terminals on the capacitor to remove any built up electrical charge. This is called shorting the capacitor.

Insert the red lead of the meter into the front connector marked "ohms." Place the black meter lead into the front connector identified as "com." Turn the meter dial to "RX1 or X1 ohm." Touch the metal ends of the meter leads together. The meter display must read "0 ohms."  The meter is ready to test the capacitor.

Touch one of the meter leads to one of the capacitor terminals. Touch the second lead from the meter to the other capacitor terminal. If the dial on the meter slowly moves to the right and back down again, the capacitor is good. If the display needle immediately goes to the right and stays there, the capacitor has an internal short and is bad. If the display needle does not move at all, there is an internal break in the capacitor and it is bad.

Testing the capacitor with a digital multimeter is even easier. Insert the meter leads as described above. Note on the switch of the meter there should be an icon that looks like
-|(- this is the symbol for a capacitor. Touch the leads to the terminals. The meter will display "good" or "bad."

Testing the relay is a basic hearing test. If you hear an audible click when the pressure tank is calling for water and the system builds pressure the relay is good. If no audible click is heard, the relay is bad. There are various types of pump relays on the market with different internal configurations. Due to this variety it can be difficult to troubleshoot the relay. The basic hearing test will work in most cases. The relay is weatherproof sealed and no internal parts are serviceable. The operation of the relay is controlled by the pressure switch closing -- turning on and opening -- turning off.