Solenoid Valves
Solenoid valves are usually considered an accessory in the process valve industry; however, while there is some truth to this, these accessories are crucial to the proper operation of any system that uses them.
The solenoid valve has many features that need to be considered when creating a specification. Eight specification points should be addressed to correctly choose the right solenoid valve for an application. These specification points are:
- Type
- Operation
- Media
- Size
- Pressure
- Atmosphere
- Voltage
- Extras
More information on these eight points is included in this article.
TYPE
Figure 1. 2-way solenoid valves used to start and stop the flow of media in a pipe trainThe type of solenoid valve refers to whether that valve is a 2-way, 3-way or 4-way. A 2-way valve (Figure 1) has two port connections-a pressure or input port (port 1) and an outlet port (port 2). These valves are used to stop the flow of a fluid or start the flow of a fluid in a piping configuration. Usually, a 2-way valve is referred to as a 2/2 valve, which means the valve has two ports and two positions. The positions are: 1) on or energized and 2) off or de-energized.
Three-way valves (Figure 2) are those that have three ports-a pressure or inlet port (port 1), a cylinder port (port 2) and an exhaust port (port 3). A 3-way valve’s most common application is for process valve automation. The solenoid valve sends air to a spring return actuator or cylinder, which creates rotational or linear movement to open or close a process valve. In this case, the media is usually compressed air or gas that is creating work, which is where the term “fluid power” is derived. The power of a compressed gas or pressurized liquid is controlled to create mechanical work. Three-way valves are usually referred to as 3/2 valves-they have three ports and two positions.
Figure 2. Basic 3- and 4-way valves typically used for process valve automationFour-way valves (Figure 2) can have four or five ports-a pressure or inlet port (port 1), two cylinder ports (ports 2 and 4), and one or two exhaust ports (port 3 and possibly a port 5). The exhaust ports can either have both cylinder ports sharing a common exhaust port or have each cylinder port with its own exhaust port. This valve’s primary use is also for process valve automation. For double-acting or non-spring return actuators and cylinders, a 4-way valve must be used. Air flow in a 4-way valve is more complicated than air flow in some other types. For example:
- In cases where the valve is de-energized or off: The pressure port to cylinder port 2 is open while cylinder port 4 to exhaust is open.
- In cases where the valve is energized or on: The pressure port to cylinder port 4 is open while cylinder port 2 to the exhaust is open.
Since the actuator or cylinder does not have a spring on one side, it must rely on fluid power from a 4-way valve to open and close. Four-way valves can be referred to as 4/2 or 5/2 valves, and they can have four or five ports and two positions.
There are other configurations such as the dual solenoid, fail-in-last-position, 3/3, and 5/3 solenoid valves, but explanations are best left for another article.
