Diaphragm valve - fully open

The first leak to check is within the regulator To see if there is gas leakage past the diaphragm, rotate the pressure adjusting valve CCW until it is fully open, then slowly open the main tank valve. If any gas leaves the regulator, the regulator is defective or broken and needs repair or replacement. 

If flow control is required, the valve should be capable of giving smooth control over the full range of flow, from fully open to closed. Globe valves are normally used, though diaphragm valves are also common. Butterfly valves are often used for the control of gas and vapor flows. Automatic control valves are usually globe valves with special trim designs. 

The operation of a control valve involves an air supply that positions its movable part (i.e. plug, ball, or vane) relative to the stationary seat of the valve. A valve actuator accurately locates the valve plug in a position determined by the pneumatic control signal and operates to move the valve to either fully open or fully closed positions. The actuators may be either piston or diaphragm types. Air-to-open valves require air to open and therefore automatically close in the event of fail closure. They are therefore used on fuel lines to furnaces. Air-to-close valves fail to open on a loss of air pressure and are used on air lines into fuel burners. In general, fail-to-open and fail-to-close valves operate when the supplied air pressure drops below a minimum value. 

Manually operated valves with local indicators control the flow of brine to individual electrolyzers. All the electrolyzers in the circuit are fed from a common header that is maintained at a specified pressure. This approach reduces the interaction between electrolyzer feed rates when any one is adjusted. Total cell room flow can be changed by changing the header pressure. The pressure is measured by a transmitter with a capillary and diaphragm seal. Wetted parts should be tantalum or PTFE. The range is usually 0-200 kPa. The control valve, located upstream of the pressure measurement, should be a fully lined fail-open butterfly valve. 

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