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Chapter 8CONTROL DEVICES

Solenoid valves

Solenoid valves consist of an electrical coil and an iron spindle with a gas valve attached to one end.

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Solenoid operation

• When electricity flows through the coil, it becomes a very strong electromagnet.

• The electromagnet has sufficient strength to lift the iron spindle.

• When the electrical supply to the coil is switched off, the gas valve loses its magnetism and the valve is returned to the off position by its own weight.

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Solenoid—uses

• Wherever electrical controls are used to control the supply of gas to a burner.

• Two solenoid valves are fitted in some cases to lessen the chance of gas leaking through.

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Relay valves

• Used in conjunction with safety devices, thermostats, etc., to control the flow of gas to the main burner.

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Combination controls

Combination controls contain multiple valves, e.g. thermostat, regulator, safety device.

They control separately and independently of each other.

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Robertshaw Unitrol

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Minisit control

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Honeywell combination control

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