Opening/Closing Time - Control Valves & On-Off Valves

Hi Sini_4s,

It depends on the how the valve is operated, what size it is, what pressure it is working at, medium flowing through the valve, make of valve, part number, etc.

The more information we have the more we can advise you.

Best regards,

John

Dear jesw55,

Thanks for the reply.

All i want to ask is there any specific formula to calculate.

Consider the size:-2" , #150, 150 Deg C, globe valve

Hi sini_4s,

The particular valve you have quoted, a globe valve, as far as I'm aware is a "screw down valve" and is manually operated so a time for the valve is not really possible.

The usual valve that has open / closed operation you can time are 90 Degree actuated or solenoid operated valves. On / Off solenoid valves usually have a response time quoted.

Best regards,

John

Using a stopwatch.

The time required to open and close a valve has more to do with the actuator than with the valve trim.

If the actuator is electric, it's a simple matter of calculating time based on stem travel distance, motor speed, and gear ratio.

If the actuator is pneumatic, the actuation time is a function of air supply pressure, pressure required at the actuator to achieve the desired position, the volume of the actuator chamber, and the restrictiveness of the tubing and other components feeding air to the actuator. This will be a more complicated calculation than for an electric actuator. A crude approximation could be made based on the air flow capacity of the supplying device (I/P, positioner, solenoid -- whatever device controls the air to the actuator), the volume of the actuator chamber, and the desired pressure change inside the actuator to move the valve.

Dear Tony,

Is there any specific formula for calculation of time.

If we consider 2" ball valve,with 4 bar air supply actuator volume -15 litres solenoid valve operated.

5-10 sec, depending on the size of the feed air line and the size of the port in the solenoid valve.

Is there a time issue with this particular process, then?

generally the required time for full close or full open is specified by the process engineers based on the process requirements - and based on this the actuator is designed ( in case of pneumatic actuators) to either vent the pressure or pressurise depending on the time. Say less tha 10 secs or less than 2 secs etc.

An actuator is sized according to the torque required for the process. based on this also again to make it open or clase faster we can give additional accesories say a quick exhaust to open the valve faster or close tha vlave faster.

If you have already have the control valve in the field use a stop watch.

If this is design, then again all the details are required. ( say for pnuematic- volume / port size /pressure etc)

Hope this helps

Best Regards

Naveen Menon

hello naveen/pwslack,

I think i am not able to put my question properly.

True we size an actuator which have certain volume. then we use solenoid valve to operate the actuator which too have a orifice/ CV value.

So if the air supply is 4 bar , orifice size of Solenoid valve is 2.4mm/Cv=0.12 & actuator volume is 2 litre what would be the opening /closing time of the valve considering it's pneumatically operated valve with solenoid valve & AFR as accessories.

The forum is in no better position to answer the question than a local Instrument Technician with some sort of clock.

It may not be as simple as you might think. The flow through the solenoid valve and into the actuator are constantly changing as the D/P is reducing as the actuator fills up with air.

You can't just crunch the numbers of flow verus volume because the valve might start to travel and even finish travelling long before the actuator is fully pressurized to equal the instrument air supply pressure.

Actuators always have to be slightly over sized to overcome friction and dynamic forces from the process fluid and to allow for firm seating.

For On Off Valves, as per SHELL DEP Closing Time 1"/Sec ( Fail Close )

Regards

Jose

What are the consequences of the actual operating time being at variance with the calculated operating time?

A valve is open whenever it isn't closed.