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Control Valve · Glossary

What is Air to Open?

Symbol: ATOactuator actionControl Valve

Air to open means air pressure on the actuator opens the valve and the spring closes it, so the valve fails closed.

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Air to Open Explained

Air to close is the opposite: air closes the valve and the spring opens it, so it fails open. The choice follows the required fail safe position.

In the control system, a reverse acting valve may need the controller output inverted so the loop still works correctly.

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Calculators for Air to Open

CalculatorActuator Bench Set CalculatorFree online calculator with formula and worked example.CalculatorActuator Thrust CalculatorFree online calculator with formula and worked example.

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Free downloadControl Valve Datasheet Template in Excel with Cv CheckFree download in Excel and PDF.

Frequently Asked Questions

What is Air to Open?

Air to open means air pressure on the actuator opens the valve and the spring closes it, so the valve fails closed.

Is air to open the same as fail closed?

For spring return actuators, yes.

Where is the action shown?

On the data sheet, the P&ID (FC or FO) and the actuator nameplate.

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All control valve terms · Full glossary A to Z

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