Pneumatic ball valve selection three points of attention

Pneumatic ball valve selection three points of attention

Pneumatic ball valve is a kind of pneumatic actuator widely used in modern automatic control system. The control signal drives the ball valve switch action through the pneumatic actuator to complete the switching control or regulating control of the medium in the pipeline.

The first point: ball valve selection

Connection mode: flange connection, clamp connection, internal thread connection, external thread connection, quick fitting connection, welding connection (butt welding connection, socket welding connection)

Valve seat sealing:
Metal hard sealing ball valve, that is, valve seat sealing surface and ball sealing surface for metal to metal ball valve. Suitable for high temperature, containing solid particles, wear resistance. Soft sealing ball valve, seat using PTFE, polystyrene PPL elastic sealing material, sealing effect is good, can achieve zero leakage.

Valve materials:
WCB cast steel, low temperature steel, stainless steel 304,304 L, 316,316 L, duplex steel, titanium alloy, etc.

Operating temperature: normal temperature ball valve, -40℃ ~ 120℃. Medium temperature ball valve, 120 ~ 450℃. High temperature ball valve, ≥450℃. Low temperature ball valve -100 ~ -40℃. Ultra-low temperature ball valve ≤100℃.

Working pressure: low pressure ball valve, nominal pressure PN≤1.6MPa. Medium pressure ball valve, nominal pressure 2.0-6.4MPa. High pressure ball valve ≥10MPa. Vacuum ball valve, ball valve of less than one atmosphere.

Structure: floating ball valve, fixed ball valve, V ball valve, eccentric half ball valve, rotary ball valve

Flow channel form: through ball valve, three-way ball valve (L channel, T channel), four-way ball valve

The second point: pneumatic actuator selection

Double acting piston pneumatic actuator. The main cylinder, end cover, piston. Gear shaft. Limit block, adjusting screw, indicator and other parts. The piston is driven by compressed air. The piston is set into a rack to drive the gear shaft to rotate 90 degrees, and then drive the ball valve switch action.

Single acting piston pneumatic actuator. Mainly in the piston and the end cover to add a return spring, can rely on the spring driving force in the case of air source pressure failure to reset the ball valve, maintain the open or closed position, to ensure the safety of the process system. So choose single acting cylinder is to choose a good ball valve is normally open or normally closed state.

The main types of cylinder are GT cylinder, AT cylinder, AW cylinder and so on.

GT appeared earlier, AT is an improved GT, is now the mainstream product, can be installed with ball valve bracket free, faster, more convenient than bracket installation, but also more firm. Can adjust 0° and 90° position, convenient installation of various solenoid valves, travel switch, handwheel mechanism accessories. AW cylinder is mainly used for large diameter ball valve, large output force, the piston fork structure.

The third point: the selection of pneumatic accessories

Solenoid valve: double acting cylinder is generally equipped with two five-way solenoid valve or three five-way solenoid valve. Single acting cylinder can be equipped with two three-way solenoid valve. Voltage can choose DC24V, AC220V and so on. Explosion-proof requirements should be considered.

Travel switch: The function is to convert the rotation of the actuator into contact signal, output to the control instrument, and feedback the switching status of the field ball valve. Commonly used mechanical type, magnetic induction type. Explosion-proof requirements should also be considered.

Handwheel mechanism: installed between ball valve and cylinder, can be changed to manual switch in case of air source failure, to ensure system safety, not to delay production.

Air source processing element: there are two and three couplings, the function is filtering, decompression, oil mist. It is recommended to install the cylinder to avoid cylinder jamming caused by impurities.

Valve positioner: For the proportional control pneumatic ball valve needs to be installed, more used for pneumatic V ball valve. Enter 4-20

mA, to consider whether there is a feedback output signal. Whether explosion-proof is required. There are ordinary type, intelligent type.

Quick exhaust valve: speed up the pneumatic ball valve switching speed. Installed between the cylinder and the solenoid valve, so that the gas in the cylinder does not pass the solenoid valve, rapid discharge.

Pneumatic amplifier: Installed in the air path to the cylinder to receive the positioner outlet pressure signal, provide a large flow to the actuator, used to improve the speed of valve action. 1:1 (signal to output ratio). Mainly used to transmit pneumatic signals to long distance (0-300 meters), reduce the impact of transmission lag.

Pneumatic holding valve: mainly for the air source pressure interlock operation, when lower than the air source pressure, cut off the valve gas supply line, so that the valve to maintain the position before the air source failure. When the air source pressure is restored, the air supply to the cylinder is resumed at the same time.

Pneumatic ball valve selection to consider the factors of ball valve, cylinder, accessories, each choice of error, will affect the use of pneumatic ball valve, sometimes small. Sometimes the technical requirements cannot be met. So the selection must be aware of the process parameters and requirements.