3/2 Way Solenoid Valves

What does 3 way mean?

3 Way or 3 port solenoid valves refer to the line connections in that there are 3 ports which makes them ideal for diverting flow from one path to another. Unlike 2 way valves that are intended for isolation purposes, 3 way valves are used for directional control and have 3 function variants – normally closed (NC), normally open (NO) and universal (U).

3 way solenoid valves are used with liquid or gaseous media and can incorporate a huge variety of options:

• Environmental – IP65, IP67, ATEX, IECEx, …
  
• Functional – manual override, manual reset…
  

In addition to material options for the valve body and elastomers for compatibility with a wide range of gases and liquids.

Normally closed, normally open or universal?

Unlike 2 way valves, 3 way solenoid valves will usually have 2 ports open at any one time and which ports are open while the coil is de-energised determines the function.

Normally closed (NC) 3 way valves block the path between the inlet and outlet ports until the coil is energised. The outlet port is connected to the exhaust port when de-energised and this path becomes blocked once the coil is energised, linking the inlet and outlet instead.

Normally open (NO) means that the valve is open and fluid flows from the inlet to the outlet and the exhaust port is blocked when the coil is de-energised. When the coil is energised, the inlet port will close and the flow path from the outlet to exhaust is opened.

Universal valves can be piped as either NC or NO as well as being used as diverting or selecting functions as the valves can accept flow in any direction. Note that this usually reduces the maximum working pressure compared to an equivalent NC or NO valve.

Pilot operated or direct lift?

Solenoid valves operate using electromagnetic attraction to move the valve from the seat and most often, a spring to return the valve to the start position. This direct lift principle works well for small valve sizes or very low pressures but as valve sizes increase, the size of coil and its power consumption rises exponentially making it bulky and expensive.

Pilot operation is the opposite of the direct lift principle in that the main force required to open the valve is provided by the media pressure. The solenoid coil can be very small as it only controls the flow of a small diameter impulse line that allows the fluid to open the main diaphragm or piston.

In a 3 way valve, the pilot can be referred to as Internal or External, meaning that the pilot fluid is taken from the inlet (Internal) or from an additional external port (External).

Internal piloted valves require a minimum operating pressure in order to overcome internal forces to change the valve state. External piloted valves however, can be used on very low pressure systems and even on vacuum where the valve is suitable.

Many 3 way valves are used in pneumatic circuits for controlling the direction of linear and rotary actuators, using compressed air or gas as the flow medium. Consideration should be given to the safe release of the exhausted gas to prevent potentially harmful contamination or even release fo flammable gas to the atmosphere.

Some valves have a non-breathing design which means that the pilot exhaust which is normally passed straight to atmosphere, is vented internally to the exhaust port to prevent any external ingress of corrosive or flammable gases.

Manual Reset or Auto Reset?

The majority of 3/2 solenoid valves are of the Auto Reset type which means that the valve will change state without external operator influence which is ideal for process automation.

There are occasions where safety requires that a valve cannot be remotely operated by a control system without an additional human input directly at the valve. This is what is known as Manual Reset. To cause the valve to change from its rest state, the coil must be energised and the lever or knob pulled to the fully open position. If the valve is energised without the manual intervention, it will not open.

There are other forms of manual reset with different operating characteristics.

Manual Latching is where the valve is opened by hand and will not close until the coil is energised. This is also known as electrical trip or electrical release.

Automatic Latching Lever is almost the opposite of this in that the valve is energised to change state which releases the lever. The lever falls due to gravity and holds the valve in the open position regardless of whether the coil is energised on not. The lever has to be manually operated in order to return the valve to the closed rest position.

3/2 Solenoid Valves

C Series 3/2 Auto Reset Solenoid Valves

F Series 3/2 Manual Reset Solenoid Valves

D50 3/2 NAMUR Solenoid Valve