David Duckworth
David Duckworth is the Director of Training and Development at Commercial Kitchen Parts & Service in San Antonio , Texas .
“ A WATER LEVEL CONTROL HAS TWO FUNCTIONS : IT ALLOWS THE TANK TO AUTOMATICALLY FILL AND MAINTAIN WATER AT A SET LEVEL , AND IT INCLUDES THE LOW WATER CUTOFF FEATURE DESCRIBED ABOVE .”
WHAT ARE THEY USED FOR ?
The majority of all equipment that uses water to generate hot water or steam utilizes some type of water level control . One type is called a low water cutoff control . This control is used to simply shut down the heating circuit if the water drops below a safe level . On electrically heated units , if the water drops below a safe level , the emersion elements would be exposed to the air and burn out ( dry fire ). When you have a gas-heated unit and the water drops below a safe level , you risk damaging the tank that holds the water .
A water level control has two functions : it allows the tank to automatically fill and maintain water at a set level , and it includes the low water cutoff feature described above . When the unit is turned on , the control senses if there is water in the tank and turns on a fill solenoid if needed . Once the control senses that the safe water level has been reached , it allows the heat circuit to start while it is completing the water fill process . How Do They Work ?
These controls use a transformer , two relays , and two probes to operate . The transformer serves two purposes : it is a step up transformer and an isolation transformer . The primary side ( 120V ), or supply voltage side , has a potential to ground . If you were to read from the hot wire to ground , you would read 120 volts AC . If you were to touch the hot wire to ground , you would experience a dead short . The secondary side ( 300V ), or output side , of the transformer has no potential to ground because it is isolated . In this case , the voltage is created by a magnetic field , so if you were to read either wire to ground , you would read zero volts . If you were to touch either wire to ground , nothing would happen .
One of the wires on the secondary side of the transformer is connected to the body of the tank or grounded to the tank . The other wire from the secondary side is connected to one side of the fill relay coil . The other side of the fill relay coil is connected to a water level probe ( short probe ) screwed into the tank . The probe is isolated from the tank ’ s body by plastic or a Teflon sleeve .
When voltage is applied to the water level control , the fill relay ’ s normally closed contacts supply voltage to the fill solenoid , opening the valve to start filling the tank . When the water reaches the bottom of the water probe , the water AC
current flows from the wire connected to the tank ’ s body through the water to the probe , completing the circuit . The completed circuit supplies voltage to the fill relay coil , energizing the coil and opening the closed contacts and dropping voltage from the fill solenoid . The low water cutoff portion of the control operates the same way , except the heat relay ’ s contacts are normally open and they close when water reaches the bottom of the long probe . The closed contacts then apply voltage to the heating circuit . What Will Happen When ? The ground wire to the tank is broken : If the secondary side wire going from the transformer to the tank body is broken or loose , there would be no continuity through the water to the probes to complete the circuit . The water solenoid would stay energized and overfill the tank with water , and the heat circuit would never energize . The short probe wire breaks ( water level ): If the wire from the short probe to the fill relay coil is broken or loose , there would be no continuity through the water to stop the water fill solenoid . The tank would overfill with water . The heat circuit would still work . The short probe is grounded ( water level ): If the wire or short probe is grounded to the tank body , there would be continuity all of the time in the fill circuit . The tank would never fill with water or the heat circuit would never energize . The water level control acts as if there is water in the tank completing the circuit . The long probe wire breaks ( heat circuit ): If the wire from the long probe to the heat relay coil is broken , there would be no continuity through the water to energize the heat circuit . The tank would fill with water to the proper level . The heat circuit would never activate . The long probe is grounded ( heat circuit ): If the wire or long probe is grounded to the tank body , there would be continuity all of the time in the heat circuit . The tank would start to fill with water and the heat would turn on immediately and could damage the tank or elements . commercialkitchen . com