Tags: Diaphragm Valves

Pilot-Operated Diaphragm Valves


A pilot-operated diaphragm valve is used to provide automatic shutoff of main line gas when there is an unstable pilot flame or no flame at all. These valves are operated by electrical energy (millivoltage) produced by the pilot generator. Their operation is controlled by the room thermostat, limit devices, and other operating controls.

The ITT General Controls B60 gas valve (see Figure 5-43) is an example of a pilot-operated diaphragm valve commonly used with gas-fired heating equipment. Where 100 percent shutoff is required, it should be used in conjunction with a thermopilot valve (see Figure 5-44).

pilot operated diaphragm valve Pilot Operated Diaphragm Valves

ITT B60Y Pilot Operated Diaphragm Valves

Diaphragm Valves


The following are the three principal diaphragm valves, each distinguished by the kind of power used to actuate them:

• Hydraulic-actuated valves
• Solenoid-actuated valves
• Heat-motor-actuated valves

A hydraulic-actuated valve utilizes a hydraulic element to provide both the thermostatic sensing means and the power for valve operation. The closed hydraulic sensing and actuating device consists of a bulb, capillary tube, and a bellows or diastat (see Figure 5-18). Temperature changes cause the liquid in the remote-bulb sensing device to expand or contract. This expansion or contraction of the liquid operates the valve by controlling the pressure exerted against a bellows in the valve body.

Unitrol 7000SR Diaphragm Valves

Both solenoid-actuated diaphragm valves and heat-motor-actuated diaphragm valves are described elsewhere in this chapter (see Solenoid Gas Valves, Oil Valves, and Direct-Acting Heat Motor Valves).

The term diaphragm valve can be confusing because valves that use a diaphragm are usually referred to by the power used to actuate them (e.g., hydraulic-actuated valves, solenoid-actuated valves) or their specific function (e.g., electric gas valves, oil burner valves).

A diaphragm valve is any valve that contains a diaphragm; its purpose is to respond to pressure variations. Because this is an essential feature of pressure regulators, the operating principles of a diaphragm valve are described in the sections Gas-Pressure Regulators and Combination Gas Controls.