Can double-acting valves be used for the emergency shut-off valves in the tank farm pipelines?

@stone2000 @*lihuagong @ylb913 @HaichuanXiaodangjia @HSLJHZ

For emergency shut-off valves, it is still recommended to use single-acting valves. The choice between single-acting and double-acting cylinders is determined by the operating conditions in place. For example, in certain piping systems where the air supply fails, it is necessary for the valve to remain either open or closed; in such cases, a single-acting cylinder is required. Single-acting cylinders have springs inside them – when there is no air supply, the valve remains closed, which is what is referred to as a normally closed valve. When air is supplied to the cylinder, it compresses the spring, and when the air supply is cut off, the spring returns to its original position, causing the valve stem to move and close the valve. If it is needed that the valve remains open even when the air supply is interrupted, simply set the initial position of the valve to open during assembly. Single-acting cylinders use less air compared to double-acting cylinders, but they exert less torque or thrust. Double-acting cylinders require air supply to both open and close the valve, while single-acting cylinders only need air supply to achieve opening or closing. Single-acting valves are mostly used for shutting off, while double-acting valves are mainly used for regulating.

Is the intention behind the original poster’s question to use a double-acting valve, so as to ensure a safe shut-off in emergency situations? In fact, this situation needs to be taken into account, but for the sake of the overall system security, emergency shut-off valves are not just one single component. By using a double-acting valve, the safety factor is lower than that achieved by connecting two single-acting valves in series. In terms of setup, these two single-acting valves are quite far apart.

Thank you. Do single-acting valves require consideration of spring life? Additionally, single-acting valves do require a higher gas pressure.

Product overview of pneumatic emergency shut-off valves: Ammonia pneumatic shut-off valves feature excellent technical performance, low pressure loss, and high reliability. Installed on ammonia pipelines and used in conjunction with remote air sources, they allow the valve to be opened and closed using the air supply. This enables rapid manual release of pressure from the air source in the event of a major leak or even a fire in the pipeline or storage tank. When the temperature reaches ≥75% p5C%D, the fusible alloy melts, causing the cylinder to automatically release pressure and the valve to close quickly, thereby preventing leaks and protecting human safety. A pneumatic cut-off valve is a type of valve used as an actuator in automated systems; it consists of a multi-spring pneumatic diaphragm actuator or a floating piston actuator together with a control valve. It receives signals from control instruments in order to regulate the flow of fluid in the process pipeline, either by shutting it off, opening it, or switching it between different states. It features a simple structure, high sensitivity, and reliable operation. It can be widely applied in industrial production sectors such as petroleum, chemicals, and metallurgy. The air source for pneumatic cut-off valves requires filtered compressed air, and the medium flowing through the valve body should be a liquid or gas free of impurities and particles. Product performance specifications for pneumatic emergency shut-off valves: Pressure rating: 2.5/4.0 Mpa. Working pressure of the cylinder: ≤2.0 Mpa. Operating temperature range: -40~+80°C. Media used in the cylinder: Nitrogen, anhydrous air. Media that can be used: Natural gas, liquefied gas, liquid ammonia. Time required to achieve full closure at ±70°C: ≤5 seconds. Opening pressure of the cylinder: ≥0.3–0.6 Mpa. Valve body materials: Cast steel WCB, stainless steel 304, 316, 316L. Types: Normally open, normally closed. Precautions for installing pneumatic emergency shut-off valves: 1. When storing the valve, seal all external connections using plugs or covers. Store it in a dry and well-ventilated area. Regular inspections should be carried out during long-term storage to remove dirt, and rust preventive oil should be applied to the surfaces to prevent rusting. 2. Before installation, this valve should be thoroughly cleaned, and all threaded connections should be tightened. 3. The emergency shut-off valve operates on the principle of a check valve and can only be used for shut-off in one direction. When installing it, attention must be paid to the valve markings, with the end that needs to be protected designated as the valve inlet. Valve installation direction: high in, low out. 4. The order must specify the type of flange sealing surface, pressure rating, and connection standard. Liquid ammonia valves, ammonia gas valves, pneumatic emergency shut-off valves

Product Name and Model: Manual/Pneumatic Dual-Operation Ammonia Shut-Off Valve QDQ641F-25C. Product Overview: The manual/pneumatic dual-operation ammonia shut-off valve features excellent technical performance, low pressure loss, and high reliability. It is installed on pipelines for liquefied petroleum gas (gas), liquid ammonia, and gas phases, and is used in conjunction with remote gas sources. The gas source is utilized to control the opening and closing of the valve; this allows for rapid manual release of pressure from the gas source in the event of a large leak or even a fire in the pipeline or storage tank. Additionally, when the temperature reaches 80°C or higher, the fusible alloy melts, causing the cylinder to automatically release pressure and the valve to close quickly, thereby preventing leaks and providing safety protection. High-pressure cut-off valves are widely used in safety systems for chemical hazardous materials, gas supply network systems, gas thermal power plant workshops, gas boiler rooms, and residential homes. The manual/pneumatic dual-use ammonia cut-off valve is a type of valve that serves as an actuator in automated systems. Combining the advantages of globe valves, check valves, solenoid valves, and pneumatic valves, this cut-off valve consists of a multi-spring pneumatic diaphragm actuator or a floating piston actuator together with a control valve; it receives signals from control instruments to regulate the flow of fluid in the process pipeline, either by shutting it off, allowing flow, or switching between these states. It features a simple structure, high sensitivity, and reliable operation. It can be widely applied in industrial production sectors such as petroleum, chemicals, and metallurgy. 1. A two-position three-way solenoid valve is installed at the air supply inlet of the shut-off valve, allowing the valve to be controlled via a remote electrical control panel. 2. When the gas leak detector triggers an alarm, the solenoid valve is activated to release gas, and the valve closes automatically. 3. The solenoid valve can be controlled manually (by pressing the red button) to release gas, after which the valve closes automatically. Technical specifications of the manual/pneumatic dual-use ammonia cut-off valve: Pressure rating: 1.6/4.0 Mpa; Working pressure of the cylinder: ≤2.0 Mpa; Operating temperature: -40~+80°C; Medium used in the cylinder: nitrogen or anhydrous air; Media that can be handled: natural gas, liquefied gas, liquid ammonia, gases; Shut-off time at ±70°C: ≤5 seconds; Opening pressure of the cylinder: ≥0.3-0.6 Mpa; Valve body material: cast steel or stainless steel. Springs: 304, 316, 316L; material: 50CrVA (spring steel). Cylinder and piston: ductile iron. Seals and O-rings: polytetrafluoroethylene, nitrile rubber. Electrical protection rating: CEI IP65/IP67. Explosion protection rating: Eexm II T4/Eexm II T5. Operating voltage and power: AC 24V or 220V, 50Hz/14V ； DC: AC12V/8.5W, AC24V/8.5W; Types: normally open, normally closed. Operating procedures for manual/pneumatic dual-operated ammonia shut-off valves: 1. The operating pressure of the valve’s cylinder should be ≥0.3–0.6 Mpa; the normal working pressure of the cylinder must not be lower than 0.4 Mpa to ensure proper functioning of the valve. 2. In normal operation, the valve remains in the open position; the solenoid coil is powered off, so no electrical energy is consumed. 3. When an accident occurs, the valve coil is energized instantaneously, triggering the valve to close rapidly and enter a self-locking state. At this point, even if the power is disconnected, the valve remains in its self-locked state and will not open automatically again. 4. Gas supply will be restored only after the staff has dealt with the accident and manually reopened the valve. 5. The medium flowing through the valve body should be a gas free of impurities and particles. 6. Operating environment temperature: -15～60℃. 7. The pneumatic liquid ammonia shut-off valve operates on the principle of a check valve, allowing flow in only one direction; it is necessary to pay attention to the valve markings during installation, with the end that needs to be protected being used as the valve inlet. Valve installation direction: high in, low out.

It should be a single-acting type; in the event that the cable gets damaged and causes a reverse flow, the spring will be used to close the valve.