Is it possible in a single modulating control valve to have a faster opening in emergency (on-off function), even when the normal opening/closing times (during modulating function) are much slower?

What are the additional features which make this fast opening function (acting as override to modulating function) possible? How much fast opening times are practically achievable?

 

I suppose it would be possible to put a three-way solenoid valve in the air supply line to the pneumatic control valve diaphragm operator. One position would be normal valve operation, a second position would be full air pressure, and the third would vent to the atmosphere. You have to figure out which is open or closed. You would also need to force the control loop that is feeding the control valve into manual.

You should also know that control valves are rarely designed for tight shut-off, that you may want for emergency conditions. It is recommended that you do not do emergency shutdown with the control valve for this reason. Instead, a remote operated ON-OFF valve should be added to the process either as a blocking valve in the process flow before the control valve if the shutdown state is no-flow,
or as a bypass valve if full-flow is the desired shutdown condition.

Dick Caro
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Richard H. Caro, Certified Automation Professional, CEO, CMC Associates,
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +.978.764.4728
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First, determine the fail safe position. Order the proper valve for fail safe. Place a simple solenoid valve into the control air line for the actuator.

When needed for a fail safe, use a digital input to vent the control air.

Failed safe by order of the control system!

 

Overriding & modulating functions are two different layers of protection achieved through different set of hardware and hence should not be shared as per existing standards and engineering practices. If the final control element (valve) is same, it turns out to be shared, but if the failure of the valve do not have major consequences, you may deviate.

Technically a control valve may be made to operate faster on demand by use of Solenoid Valve as suggested by Mr. Caro. Mostly SOV is used to immediately achieve "fail-safe" position of the valve by bleeding air from actuator chamber through SOV with suitable orifice (port) size.

Minimum achievable time depends on the existing valve parameters like, stroke length, packing friction, spring paramaters,whether the valve has soft seat etc.

It also depends on valve accessories connected and tubing size/length.

Regards.