Types of Fast-acting On/Off Valves with Built-in Actuators

 Types of Fast-acting On/Off Valves with Built-in Actuators

Solenoid Valves

Solenoid valves operate using a linear sliding obstructer that opens and closes the valve, or changes the flow from one outlet to another. There are many different types of obstructers used including plunger, shuttle, spool, and diaphragm.

The linear motion is achieved by energizing an electromagnetic coil to pull the obstructer in one direction. A spring drives the obstructer back in the opposing direction when the coil is de-energized. 2-position on/off valves are the most common type of solenoid valves, but there are a vast number of others, including 3-position where there are 2 coils that pull the obstructer in opposite directions, using springs to center it when neither is energized.

There are even proportional solenoid valves that can be used for flow control. In these valves, the coil moves the obstructer varying distances based on the voltage supplied to it.

Solenoid valves are relatively small. Their size is limited by the strength of the coil which is a result of the windings used to create a magnetic field when energized. In addition to the limit on strength of the coil, the flow paths and orifices in solenoid valves are rather small when compared to the line size. This limits flow and increases the pressure drop through the valve.

Common everyday applications include the water line on dishwashers and ice makers. In industrial valve automation, solenoid valves are also used to control the supply air to pneumatic actuators.

If a high flow rate or small pressure drop is required, solenoid valves are not suitable. Coaxial or angle seat valves are required.

Most solenoid valves consist of a valve body on which various coil types can be attached. The coils come in a range of voltages with a variety of connectors, and electrical protection ratings.

Coaxial Valves

Coaxial valves are 2-position valves that can be pneumatically or electrically actuated. The electric versions use an electromagnetic coil vs. a spring, similar to solenoid valves. The pneumatic versions use air pressure vs. a spring (spring return), or air pressure in both directions (double acting).

Coaxial valves use a shuttle type obstructer that the media travels through when open. This shuttle moves to one position or the other to perform its function, either on/off or diverting flow to the proper outlet. Coaxial valves have a much larger flow path compared to solenoid valves, but still do not come close to a full port valve. That being true, there is again a limit on flow and an increase in pressure drop.

There are vastly different styles of coaxial valves. Two examples are the VA series pneumatically operated on/off valves and the VAX series pneumatic or electric coaxial valves available in 2-way on/off or 3-way diverting.

For many on/off applications coaxial valves would make a good substitute for a ball valve. Coaxial valves will provide a smaller valve that operates more quickly while a ball valve will have higher flow rates with lower pressure drops. 

Angle Seat Valves

Angle seat valves are 2-position valves with a built in pneumatic actuator. The actuator can be spring return or double acting. The obstructer is a plug that enters the valve at an angle to sit in an angled seat molded into the valve's flow path. The plug gets retracted almost completely out of the flow path when open. This factor makes angle seat valves the highest flow fast-acting valves with the lowest pressure drop. In many on/off applications, angle seat valves are a perfect substitute for a ball valve. They are faster acting, less costly, and longer lasting.

Angle valves are particularly suited for use on low pressure steam applications below 150 PSI.

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