Valve Actuator

[Sailor5]

Good afternoon,

We've currently detected that one valve was specified with a closing time of 30s in our system. Due to the fact that the flow rate has been increased, a closing time of 30s would lead to overpressure in the system. However, if we increase the closing time to 100s, the resulting surge is acceptable.

Now my question: Is this attributed with a change of the hardware (actuator) piloting the valve? In other words: Does every actuator type generally has a specific closing / opening time or can one (in case of a control valve) simply solve this by ramping down the setpoint accordingly (100s ramp time from 100% to 0%) in the control system?

Your input would be highly appreciated.
Unfortunately, I do not have more information available about the current actuator being used for the valve.

Thanks and greetings,
Sailor5

 

[btrueblood]

Yes, slowing the command slew rate may work - provided the actuator motor response is reasonable, ie. it responds to every few % change in signal, rather than a 10 or 20% change in signal.

 

[gerhardl]

You have given a given a 'general discription' of an actuator (any actuator) and then asked a spsific question about regulation (by reducing the electrical input) to the actuators pilot valve. As such btrueblood has given you the answer.

If you ask whole question generally (for any valva actuator with any actuation type (el. air, hydraulic and others), the answer is that it is always possible to regulate the closing time by adjusting the closing timee by throtteling or reduce power input over time. But note: within the given physical/mechanical limits of the specific equipment.

A common fault when spcifying actuators is to overrate the neceessary closing time, resulting in to large and costly actuators, and thus possibly give surgeing problems.

This is the reason one should always specify and analyse necessary closing and opening time for any valve actuator, need for control feedback and steering signal and max and min closing.