The thermcouple, the thermopile and pilot safety switch
This part uses dissimilar metals to produce a small current that is used to hold open a pilot safety valve.
If I fuse 2 different metals such as copper and steel at one end, called the "hot junction" then heat the end, then the cold end will show a voltage. This voltage can be used to power an electromagnet that will hold a valve open. The video below takes a thermocouple apart and shows how it is made.
If I fuse 2 different metals such as copper and steel at one end, called the "hot junction" then heat the end, then the cold end will show a voltage. This voltage can be used to power an electromagnet that will hold a valve open. The video below takes a thermocouple apart and shows how it is made.
The thermocouple is mounted in a pilot assembly. There, it is heated by the pilot light to produce the electricity necessary to hold open the pilot safety. The video below explains this operation.
The pilot valve must hold the pilot valve open if the power from the thermocouple is high enough (usually 18 to 22 millivolts), and close the pilot valve if the power is too low (usually 10 millivolts).
For a look at what a separate pilot safety switch looks like inside and how it operates, check the video below.
This type of switch is seldom used anymore as the pilot safety has been incorporated into a combination gas valve.
For a look at what a separate pilot safety switch looks like inside and how it operates, check the video below.
This type of switch is seldom used anymore as the pilot safety has been incorporated into a combination gas valve.
The pilot safety used on most combination gas valves is part of the valve. The solenoid is spring loaded and will drop out when the thermocouple power reduces below about 10 millivolts. The video below shows it in operation.
the thermopIle system
In early gas appliances, many did not have electric power to the appliance. So a method was designed to operate the appliance without any outside power.
This system is called the thermopile system.
Note that the thermocouple system described above is unable to operate a solenoid, but could hold a valve open. The thermopile system could operate a solenoid in the combination gas valve as well as just keep one open. The way this is done is to build a number of thermocouples, then connect them together to produce enough power to operate a solenoid. The video below shows the difference between these parts.
This system is called the thermopile system.
Note that the thermocouple system described above is unable to operate a solenoid, but could hold a valve open. The thermopile system could operate a solenoid in the combination gas valve as well as just keep one open. The way this is done is to build a number of thermocouples, then connect them together to produce enough power to operate a solenoid. The video below shows the difference between these parts.
Thermopile systems were used mostly in early designs and did not need any outside power to operate. This meant that they could be used during power outages or in places that did not have utility power.
However, furnaces that used this method transferred heat by convection only thus they had lower efficiencies. When 120 volt power systems became popular, electric fan motors operated on 120 volts soon made these systems obsolete. The use of 120 volts to operate these systems also started the use of low voltage (24 volts)to operate the controls of these systems. The 24 volt combination gas valve became the standard of the industry.
However, furnaces that used this method transferred heat by convection only thus they had lower efficiencies. When 120 volt power systems became popular, electric fan motors operated on 120 volts soon made these systems obsolete. The use of 120 volts to operate these systems also started the use of low voltage (24 volts)to operate the controls of these systems. The 24 volt combination gas valve became the standard of the industry.
The return of the millivolt system
The popularity of gas fireplaces brought back the use of millivolt systems in mostly gas fireplaces. The fireplace or gas designed fireplace burner system became popular because it could be operated if there was a power outage. Most of these fireplaces had fans to increase their efficiency but could be operated without 120 volt power.