How is the operating mode of a control valve selected?

If it remains in the open position after the signal is interrupted and fluid flow is not disrupted, a air-operated valve should be selected； If the valve remains in the closed position after the signal pressure is lost, preventing fluid flow through the safety system, a air-operated valve should be used.

The choice of operating mode mainly involves selecting a normally open valve or a normally closed valve. The selection of air opening and air closing valves is primarily based on production safety considerations. When the signal pressure is interrupted in the system due to faults or other reasons (that is, when the valve is under no signal pressure), it is necessary to determine whether the valve should be in an open or closed state in order to prevent equipment damage and protect the workers. If the valve being in the fully open position poses little risk, a air-actuated shut-off valve should be chosen (since no signal pressure is present in the event of a failure, keeping the valve in the fully open position) ； Conversely, the gas opening valve should be selected. In other words, from a safety perspective, if the process requires fail-safe shutdown, select a gas-open valve ； If the process requires fail-open operation, select a gas shut-off valve.

What was said on the third floor is very comprehensive; I agree!

Generally, gas-operated valves are used for switching high voltage to low voltage. Such as the ammonia release valve. Gas shut-off valves are generally used to regulate the temperature of the synthesis tower. :call: