Pneumatic Angle Seat Valves - How They Work

Pneumatic angle seat valves are operated by pneumatically actuated piston for precise control of fluid flow in various industrial applications. These valves are distinguished by their angled seat design, which enhances flow efficiency and reduces pressure drop across the valve, making them highly effective for applications requiring high flow rates.This article discusses the features and operational mechanics of pneumatic angle seat valves.

Key features of pneumatic angle seat valves

Pneumatic angle seat valves have several key features:

• Fast & remote actuation: Pneumatic angle seat valves offer quick response times and can be controlled remotely, making them ideal for automated systems in hazardous areas needing rapid adjustments to flow rates.
• Zero differential pressure operation: These valves can operate effectively even without a pressure difference between the inlet and outlet, allowing for stable flow control across a variety of conditions.
• High cycle life: Designed for durability, pneumatic angle seat valves have a long service life, capable of enduring numerous open/close cycles without performance loss, reducing maintenance needs and operational costs.

However, they require compressed air and additional pneumatic solenoid valves for their operation. This requirement can complicate the system setup and increase initial costs. Additionally, these valves typically have a relatively large actuator when compared to solenoid valves, which can make them less suitable for applications where space is limited or where a more compact design is preferred.

Read our angle seat valve overview article for more details on the design and working of angle seat valves.

Pneumatic angle seat valve operation

Pneumatic actuator

A pneumatic actuator is securely mounted to the angle seat valve body. The actuator consists of a piston and cylinder arrangement, operated by compressed air. The primary role of the actuator is to control the opening or closing state of the valve with precision.

Pilot solenoid valve

A pilot solenoid valve, typically a 3/2-way solenoid valve, regulates the flow of compressed air into the actuator's chambers. The solenoid valve receives its control signal, an electrical impulse, from a control system such as a Programmable Logic Controller (PLC). This signal determines whether the valve should be in its open or closed position. The default state of the valve, either normally open (NO) or normally closed (NC), along with the positioning of a spring within the actuator, determines the valve's resting state in the absence of pneumatic pressure.

The activation (for NO configurations) or deactivation (for NC configurations) of the solenoid valve is directly influenced by the control signal. This process directs compressed air into the actuator chamber, facilitating the movement of the piston.

Air admission and piston movement

Upon receiving the appropriate control signal, the solenoid valve's activation allows compressed air to enter the actuator chamber. This pressure exerts a force on the piston, causing it to move. This linear motion is transmitted through a stem to the sealing element, which then moves to either open or close the valve. Some designs incorporate features to minimize operational noise, such as cushioning at the end positions of the actuator's movement.

Valve operation

For NO valves, the introduction of air pressure displaces the sealing element from the seat, allowing media to flow through. Conversely, for NC valves, air pressure moves the piston in the opposite direction, forcing the sealing element against the seat and stopping the flow. The design ensures that the valves revert to their default state via spring force when not pressurized.

• Note: It's essential to ensure that the air supply is within the specified pressure range for the actuator to function correctly. Additionally, the quality of the compressed air (in terms of moisture and particulate content) must be managed to prevent damage to the actuator and valve components.

Selection criteria

When choosing a pneumatic angle seat valve, there are several key factors. Read our article on angle seat valve selection for more information on the key selection parameters while choosing an angle seat valve for an application. Key factors are:

1. Valve function (NC/NO): Determine whether the application requires the valve to be normally closed (NC) or normally open (NO).
   1. Choose NC if the valve needs to stay closed when no air pressure is applied and open when air is supplied. This is common in safety applications where the default state should be closed to prevent flow.
   2. Select NO if the valve needs to stay open when no air pressure is applied and close when air is supplied. This is useful in applications where continuous flow is required unless interrupted by a control signal.

2. Connection type and size:
   1. Measure the diameter of the existing pipes and choose a valve with a matching connection size (e.g., 1/2", 3/4", 1").
   2. Identify the threading type used in the system (e.g., BSPP, NPT) and select a valve with the same threading to ensure a proper fit.

3. Housing and seal materials:
   1. Housing: Choose materials that are compatible with the media being controlled and the environmental conditions. For general applications, brass is a good choice due to its durability and corrosion resistance. For more corrosive environments or higher purity requirements, stainless steel may be preferable.
   2. Seal material: PTFE (Teflon) is ideal for chemical resistance and high temperatures, NBR (Nitrile Rubber) is suitable for oils and fuels, and FKM (Viton) is good for high temperatures and chemical resistance.

4. Temperature, pressure, and flow ratings:
   1. Temperature: Check the operating temperature of the application and select a valve that can withstand those temperatures.
   2. Pressure: Determine the maximum and minimum pressures in the system and choose a valve rated for those pressures.
   3. Flow ratings: Consider the flow rate required for the application. Valves with a Y-shaped design typically offer better flow characteristics. Ensure the valve can handle the viscosity of the media if dealing with thick fluids.

5. Flow direction: For most applications, a valve that closes with the flow direction is sufficient. If the application involves high flow velocities or the need to prevent water hammer, select a valve that closes against the flow direction. This can help mitigate pressure surges and protect the system.

Refer to our detailed article on angle seat valve actuation for more details on alternative actuation methods for angle seat valves, including electric and manual options.