Water pump pressure switches turn the pump on when the pressure inside the water system falls below a predetermined setting. Some switches are electrically connected directly to the pump. Other systems may have the switch controlling a relay. Typically this relay is used on submersible pumps in which the operational power exceeds the capacity of the pressure switches' contacts. The pressure switch can either be attached into a water pipe or a bladder pressure tank on the water system.
Most switches are factory set, but the on and off adjustments can be accessed by the homeowner. Generally the set of electrical contacts are mechanically attached to a set of springs. A small nut adjusts the tension of these springs. The tension adjustments control the on and off function of the pressure switch.
The pressure switch at times can be placed in a wet environment. This moisture can cause corrosion to form on the electrical contacts. Always shut off the electricity to the pump and control circuit when you check the contacts for any signs of corrosion or burnt areas. Clean the contacts with a small piece of emery cloth or a fine-toothed file. If the contacts are severely pitted, they may have to be replaced. Reapply the power and check the amount of voltage that is coming to the switch from the main electrical panel. Use a voltmeter and consult the pump manufacturer's specifications for voltage. Test both the incoming and the outgoing sides of the switches' contacts for correct voltage.
Debris in the water system can clogged the pressure inlet of the switch. A small opening, less than 1/8 inch in diameter, is used to move a diaphragm. This diaphragm rides against the tension springs. If the pressure inlet is clogged, it can interfere with accurate readings of the water system. The inlet can be cleaned, but this is only a temporary fix. The debris or sediment must be flushed from the water system and a filtration system may have to be installed. Permanent damage may have resulted from too much build-up in the diaphragm and the switch may have to be replaced.
The pump may experience erratic behaviour in the form of constant on-and-off operation. This can be caused by two things: low air pressure in the bladder tank and broken or poorly adjusted tension on the springs. Check the bladder air pressure by draining the water from the system. Use a tire gauge and measure the air pressure in the rubber bladder. Typically there is an air nozzle on the tank. The pressure should be in the range between 35 and 45 PSI. Fill the bladder with air from an air compressor. A bladder tank that cannot maintain a constant air pressure may be ruptured and will have to be replaced. Inspect the springs for any signs of breakage. Replace any broken springs. Adjust the tension nuts according to the pressure switch instructions. These instructions typically reside on the interior of the switches' plastic cover.