The function of the shutdown valve is to shut-off the fluid flow inside the fluid flow line or pipe when an emergency that leads to a hazardous situation comes. It is an actuator operated valve mainly used for safety purpose that is why it is called Emergency shutdown valve. It is also known as the shutdown valve or SDV, ESDV, ESV, ESD
It is very important that every instrument engineer must know where the shutdown valve is installed, what fluid flow through it and what standard is used as the design reference. These shutdown valves are commonly used in oil and gas field in order to reduce the escalation of hazards from one system to other.
shutdown valve features :
i) Tie Shut Off
- a shutdown valve must possess Zero/minimum leakage. Generally, it should pass the seat leakage testing as per API 508 and/or ISO5208.
- shutdown valve must work even though it is exposed to external fire attacks. Thus, shutdown valve body shall be fire-rated according to API 607 for soft seated valve or API 6FA for API 6A & API 6D valves or BS 6755 Part 2.
iii) Fast action (From Full Open - Full Close)
- The actions of the shutdown valve must be fast. A quarter ball valve is best for quick action. According to thumb rule, shutdown valve shall be able to close within 10 seconds of activation, and time taken from Full open to Full Close must be within 1-2 seconds per inch of shutdown valve size. Therefore, proper selection and sizing of the actuator must be ensured and all requirements must be fulfilled.
iv) Minimum passing (when closed)
- This feature is needed to minimize the potential of the overpressure of a low-pressure system and spurious trip. A shutdown valve with equal% characteristic (most ball valve will have this feature. However, this shall be confirmed with valve supplier) is the preferred type. With equal% characteristic, it can operate with 10% valve closure give 20% flow reduction, 20% closure give 50% closure.
v) Minimum disturbance / turbulence to process fluid
- This feature is to minimize unnecessary energy lost. Reduced Bore (RB) ball valve having a hole in the middle would minimize flow direction change and turbulence. Full Bore (FB) ball valve virtually like a pipe- significantly minimize energy lost.
- A shutdown valve actuator shall pneumatic/hydraulic fail-safe spring-return type. If a shutdown valve fails to close electrical driven type shall not be used.
vii) Manual field reset
- A shutdown valve must manually be operated at the site. The operator shall ensure that the system is clear and safe and also, can be reset on site. No remote reset is allowed.
Full Open Position – Normal Operation
The ESDV provides minimal pressure Differential when Differential when the valve the valve is in full-open-open position.
The full bore ball valve virtually acts like a pipe minimizing process fluid turbulence
Full Closed Position – Emergency Situation
Setpoint pressure has been exceeded and the ESDV the ESDV has fully closed providing fully closed providing tight shutoff with its double-seated design.
■ Valve Type: Trunnion mounted full port ball valve
■ Body Style: Side entry, forged body
■ Actuator Type: Single-acting, spring return
■ Instrumentation: Pneumatic
■ Size Range: 6 – 36”
■ Pressure Ratings: ANSI Class 150 - 2500
■ Shut Off: Soft seat - tested up to Class VI Metal seat - tested up to Class V
■ End Connections: RFFE, RTJ, weld end
■ Closing Time < 2 second (depending on size)