General Knowledge
Combination Gas Valve
The combination gas valve is the heart of the fryer. It allows gas to flow to the pilot and burners. It contains a gas cock knob that can be turned to "OFF," "PILOT," and "ON." It has a built-in regulator for regulating incoming gas pressure; two built-in solenoid valves, one for the pilot and another for the burners. Additionally, it has a pilot gas connection with a pilot gas adjustment section for increasing the pilot gas pressure; a pressure tap for manometers located near the gas outlet, and a pressure regulator adjustment section for increasing or decreasing the burners gas pressure. There are electrical terminals tilted "TH, TP, TR, PP, & PG". Usually three electrical terminals are on a combination gas valve sometimes labeled "TH/TP, TP, TH", "TH/TR, TR,TH", "TH, TH/PP, PP", & "TH, TH/PG, PG". There are some gas valves that have four electrical terminals labeled, "TH1, TH2, PP1, PP2".
TH = Thermostat
TP = Thermopile
TR = Transformer
PP = Powerpile
PG = Pilot Generator
The electrical terminals titled, "PP2, TH/TP, TH/TR, TH/PP, & TH/PG" are neutral/common. Electrical terminals titled, "TH" are also neutral/common. Electrical terminals titled, "TP, TR, PP or PP1, & PG" are live/hot.
Thermostat
Also known as hydraulic thermostat or mechanical thermostat, this thermostat has a bulb, capillary tube/phial, diaphragm, and dial. Inside the capillary tube and bulb is a temperature sensitive liquid. The liquid in the capillary tube and bulb expands and contracts as the temperature changes. The bulb reads the temperature inside the grease and as the temperature increases, it cause the liquid to move the diaphragm, activating a snap action switch which closes the circuit. If the bulb is damaged or if the capillary tube is kinked, this could affect the sufficiency of the thermostat.
Hi Limit
The hi limit is a safety device that keeps the grease temperature from exceeding a specific set point if the thermostat fails to close circuit. Like a thermostat, the component has a bulb, capillary tube, diaphragm, and sometimes a reset button. If the set point is reached, the hi limit will close circuit stopping the millivolts from reaching the combination gas valve thus causing the solenoid valves to close immediately. The circuit will remain closed till the grease temperature cools below the hi limit set point. The hi limit has three electric terminals titled " C, NC, & NO".
C = Common
NC = Normally Closed
NO = Normally Open
Thermopile/Thermocouple
The thermopile and thermocouple are electrical devices that transfer thermal energy into electrical energy known as millivolts. Thermopiles and thermocouples are different in appearance and one produces more millivolts than the other. Thermopiles have two wires colored red and white. The red wire is the hot leg or live wire and the white wire is common/neutral. Thermocouples are made up of different types of metal wires joined together on each end. Thermopiles can produce up to 750MV and thermocouples 35MV. In order to check the millivolts or charge, a multimeter set to DC vm is needed.
