SOMETHING ABOUT CONTROL VALVE ACTUATORS FAILURE MODES
Control valves could be constructed from various mixtures of valve actuator and valve body. The mixture of actuator and valve is usually selected to supply a particular failure mode if the instrument air supply fail unconditionally.
The most typical control valve actuator used in the market may be the diaphragm actuator. Diaphragm actuators, as with the situation of valve physiques, could be considered either direct or reverse acting.
Any failure mode could be acquired with a mix of direct or reverse acting.
1. Fail Open
2. Fail Close
Both of these failure modes is possible by an aura to shut Valve (ATC) as well as an Air to spread out valve (ATO).
Air to shut Control Valve (ATC)
An aura to shut (ATC) valve and for that reason fail open valve, could be acquired using the mixture of a reverse acting actuator along with a reverse acting valve body or perhaps a direct acting actuator along with a direct acting valve body.
Air to spread out Control Valve (ATO)
An aura to spread out (ATO) valve and for that reason fail close valve, could be acquired with a mix of direct actuator and reverse body or reverse actuator and direct Body.
Valve Body and Actuator Combination as well as their Failure Modes
The act of an actuator may be easily determined (usually by if the air is provided towards the upper or lower 1 / 2 of the housing). Direct or reverse acting valve physiques aren't always readily identifiable. Most frequently, mention of nameplate or flow sheet is generally essential to properly identify the act of a valve body – reverse acting or direct acting.
Indexed by the table here are all possible mixtures of valve body and actuator as well as their failure modes:
The most typical control valve actuator used in the market may be the diaphragm actuator. Diaphragm actuators, as with the situation of valve physiques, could be considered either direct or reverse acting.
Any failure mode could be acquired with a mix of direct or reverse acting.
1. Fail Open
2. Fail Close
Both of these failure modes is possible by an aura to shut Valve (ATC) as well as an Air to spread out valve (ATO).
Air to shut Control Valve (ATC)
An aura to shut (ATC) valve and for that reason fail open valve, could be acquired using the mixture of a reverse acting actuator along with a reverse acting valve body or perhaps a direct acting actuator along with a direct acting valve body.
Air to spread out Control Valve (ATO)
An aura to spread out (ATO) valve and for that reason fail close valve, could be acquired with a mix of direct actuator and reverse body or reverse actuator and direct Body.
Valve Body and Actuator Combination as well as their Failure Modes
The act of an actuator may be easily determined (usually by if the air is provided towards the upper or lower 1 / 2 of the housing). Direct or reverse acting valve physiques aren't always readily identifiable. Most frequently, mention of nameplate or flow sheet is generally essential to properly identify the act of a valve body – reverse acting or direct acting.
Indexed by the table here are all possible mixtures of valve body and actuator as well as their failure modes:
| Valve Actuator | Valve Body | Valve Action | Failure Mode |
| Direct | Direct | Air to Close | Fail Open |
| Reverse | Reverse | Air to Close | Fail Open |
| Direct | Reverse | Air to Open | Fail Closed |
| Reverse | Direct | Air to Open | Fail Closed |