A pneumatic ball valve is a widely used pneumatic actuator in modern automatic control systems. The control signal drives the ball valve's opening and closing actions through the pneumatic actuator, completing switch control or regulating control of the medium inside the pipeline.
Ball valve selection
Connection method
Flange connection, clamp connection, internal thread connection, external thread connection, quick connector, welding connection. (Butt welding connection, socket welding connection)
Seat seal
Metal hard-sealed ball valve, that is, the sealing surface of the seat and the sealing surface of the ball are metal-to-metal ball valves. Suitable for high temperature, solid particles, and wear-resistant working conditions. Soft-sealed ball valve, the seat adopts polytetrafluoroethylene PTFE, and the elastic sealing material for matching PPL has a good sealing effect and can achieve zero leakage.
Valve material
WCB cast steel, low temperature steel, stainless steel 304, 304L, 316, 316L, duplex steel, titanium alloy, and so on.
Operating temperature
ambient temperature ball valve, -40℃ to 120℃. Medium temperature ball valve, 120℃ to 450℃. High-temperature ball valve, ≥450℃. Low-temperature ball valve, -100℃ to -40℃. Ultra-low temperature ball valve, ≤100℃.
Operating pressure
Low-pressure ball valve, nominal pressure PN ≤ 1.6 MPa. Medium pressure ball valve, nominal pressure 2.0-6.4 MPa. High-pressure ball valve ≥ 10 MPa. Vacuum ball valve, a ball valve with a pressure lower than atmospheric pressure.
Structural form
Floating ball valve, fixed ball valve, V-type ball valve, eccentric half ball valve, rotary ball valve.
Flow channel form
Straight-through ball valve, three-way ball valve (L-type flow channel, T-type flow channel), four-way ball valve.
Pneumatic actuator selection
The double-acting piston-type pneumatic actuator mainly consists of a cylinder, end cover, piston, gear shaft, limit block, adjustment screw, indicator, and other components. Compressed air is used as power to push the piston to move. The gear on the piston integrates with the gear shaft to rotate 90° and then drives the ball valve's opening and closing actions. The single-acting piston-type pneumatic actuator is mainly equipped with a reset spring between the piston and the end cover, which can rely on the pushing force of the spring to reset the ball valve when the air source pressure is faulty to maintain the open or closed position of the ball valve and ensure the safety of the process system. Therefore, when selecting a single-acting cylinder, it is necessary to choose whether the pneumatic ball valve is normally open or normally closed. The main types of cylinders are GT cylinder, AT cylinder, AW cylinder, etc.
Selection of pneumatic accessories
Solenoid valve
The double-acting cylinder is generally equipped with a two-position five-way solenoid valve or a three-position five-way solenoid valve. The single-acting cylinder can be equipped with a two-position three-way solenoid valve.
Stroke switch
The function is to convert the rotation of the actuator into a contact signal and output it to the control instrument, feedback the opening and closing status of the on-site ball valve. The commonly used switch types are mechanical and magnetic induction. Explosion-proof requirements must also be considered.
Handwheel mechanism
Installed between the pneumatic ball valve and the cylinder, it can be switched to manual mode when the air source is faulty to ensure system safety and avoid disrupting production.
Air source treatment components
There are two-piece and three-piece structures, which filter, reduce pressure, and eliminate oil and mist. It is recommended to install to avoid impurities entering the cylinder and causing it to jam.
Valve positioner
It is necessary for proportional control pneumatic ball valves, and is mostly used for pneumatic V-type ball valves. Consider whether it comes with feedback output signals and whether it needs to be explosion-proof. There are ordinary types and intelligent types.
Quick exhaust valve
Speeds up the opening and closing speed of the pneumatic ball valve. Installed between the cylinder and the solenoid valve, the gas inside the cylinder is rapidly discharged without passing through the solenoid valve.
Pneumatic booster
Installed in the air circuit leading to the cylinder to receive the pressure signal from the outlet of the positioner and provide a large flow to the actuator to improve the valve's response speed. The signal and output ratio are 1:1. Primarily used to transmit pneumatic signals over long distances and reduce the influence of transmission lag.
Pneumatic hold valve
Mainly for continuous pressure operation, when the air source pressure is lower than the operating pressure, cut off the pipeline to maintain the ball valve's position before the air source fault. When the air source pressure recovers, the air supply to the cylinder is restored simultaneously.
When selecting a pneumatic ball valve, factors such as the ball valve, cylinder, and accessories must be comprehensively considered. Any errors in selecting any of these could affect the use of the pneumatic ball valve. Sometimes it may be minor, and sometimes it may fail to meet process requirements. Therefore, when selecting, be sure to know the process parameters and requirements.
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