Angle seat piston valves

An angle seat piston valve is a pneumatically-controlled valve with a piston actuator providing linear actuation to lift a seal off its seat. The seat is set at an angle to provide the maximum possible flow when unseated. Angle seat piston valves are particularly suited to applications where high temperatures and large flow rates are required, such as steam or water. When used in reverse some models of angle seat piston valve will eliminate water hammer when operated.

Working

Angle seat valves are 2/2-way pneumatically actuated piston valves. The piston actuator provides a linear motion to lift the seal off its seat. Because the seat is positioned under an angle, the flow is minimally impeded in the open position, resulting in an excellent flow rate and a low pressure loss. They are used to regulate the flow of liquids, gases, steam, vacuum and even aggressive fluids. They can also operate with high temperatures and high viscosity media, even under zero differential pressures. The robust design makes angle seat valves a popular choice for harsh applications and they have very high cycle lives. Therefore, they are excellent long-life alternatives to ball valves. These valves are also suitable alternatives for solenoid valves, especially with contaminated, viscous media where typical solenoid valves would fail. They may be operated using a single acting or double acting configuration, which has an influence on its pressure rating. They can also be designed as manually operated or electrically operated, but in this article we will discuss pneumatic angle seat valves.

Construction and Design

They have a robust construction similar to globe valves, but use a piston operated angle seat valve with a closure spring. The body is normally cast or die-forged in one piece. A plug is connected to the end of the piston which is seated on PTFE seats. The piston is designed to retract further from the seat, thereby providing maximum flow rate. They may be Normally Closed (NC), Normally Open (NO) or Double Acting. The piston actuator comes with threaded ports or with NAMUR ports which allows for direct mounting of NAMUR style solenoid valves. Often, the actuator head can be rotated 360° to allow optimum position of air and electric lines in tight locations. The valve body is generally made of brass or stainless steel. Connection types include threaded, clamped or welded. Typically, a visual indicator on the top of the piston shows whether the valve is open or closed.

Working Principle

Angle seat valves are operated pneumatically such that air pressure is used to control the piston actuator, which lifts the valve plug off its seat. Normally Closed (NC) valves usually have the valve closed in unpressurized conditions and use a spring to return the valve to the rest state. Normally Open (NO) valves have the valve opening always open unless air pressure acts to close it. A NO valve can be obtained if the spring is placed on the opposite side of the piston actuator. Double Acting valves can be used to handle flow in both directions. These valves have no spring and depend on the supply air to determine the valve position. These configurations influence the pressure rating of the valve. Flow up and under the valve (causing valve to open) will reduce water hammer effect but reduces the maximum working pressure of the valve by typically 50%. However, fitting a strong return spring will help increase the working pressure but a larger actuator will be required to overcome this increased spring strength. With flow over seat (causing valve to close), a full working pressure is achieved and water hammer can be reduced by restricting the compressed air supply flow.

Disadvantages of Angle Seat Piston Valves

Angle seat piston valves require a controlling 5 to 8 bar compressed air supply and an external 3/2 way miniature control solenoid valve that is used to control the compressed air supply to the valve actuator. However the miniature 3/2 way control solenoid valve can be located remotely with a single air line to the angle seat piston valve. Angle seat piston valves can be quite large in comparison to a solenoid valve as the valve has a pneumatic actuator head fitted to the body.

Pneumatically Operated Angle Seat Piston Valve Applications.

Typical applications where angle seat piston valves are used consists of but is not limited to

Air drying equipment
Autoclave equipment
Autoclave food sterilisation
Automated cleaning machines
Beer making and brewery equipment
Braking system testing
Bottling and beverage dispensing
Chemical dosing equipment
Chemical processing
High pressure casting
Ink dispensing
Kerosene filling systems
Laundry equipment
Metal cleaning machines
Paint dispensing
Pollution control equipment
Process control systems
Steam boiler dump valves
Steam control equipment
Sterlizers
Textile drying and dyeing
Vacuum mixing
Wax powder manufacturing