Figure 4-27. - An automatic gas burner control system.

Figure 4-28. - A gas pressure regulator.

The recycling solenoid gas valve shown in figure 4-30 can be used with the same heating equipment as the standard solenoid gas valve. The design of this valve differs from that of the standard solenoid gas valve, because it is equipped with an automatic recycling device that allows the valve to switch to manual operation during power failure. However, upon the resumption of power, the thermostat automatically resumes control of this valve.

DIAPHRAGM VALVE. - The diaphragm gas valve shown in figure 4 - 31 can be used

Figure 4-29. - A standard gas solenoid valve.

interchangeably with a solenoid gas valve. Its main feature is the absence of valve noise when it is opening or closing. In this type of diaphragm valve, the relay energizes and opens the three-way valve, so the gas pressure on the top of the diaphragm is released to the atmosphere. Reducing the pressure on the top of the diaphragm in this manner causes the gas supply pressure to flex the diaphragm upward, opening the main gas valve. When the relay is de-energized, the vent to the atmosphere is sealed and pressure from the 4-20