The latest entry in the Magnet-Schultz of America Solenoid 101 blog series is designed to explain the basic differences between common solenoid valve designs. This blog builds on our general overview of solenoid principles. Check our blog history for information on more technical concepts and feel free to make suggestions for future posts.
Solenoid Valve Types
Solenoid valves provide a practical means of electronic control for the flow of liquids and gases. With hydraulic and pneumatic applications spread throughout industries from automotive to food service, these devices play a massive role in modern mechanics. In order to better understand their function and terminology, we have laid out some of the basic concepts in plain terms.
- Open or Closed
- Poppet or Spool
- Direct or Pilot
- 2, 3, or 4 Way Valve Functions
Understanding these 4 categories of characteristics will create a foundational knowledge of solenoid flow control useful in any field or application requiring electronic flow control.
1. Normally Open or Normally Closed
When describing the function of the solenoid valves, normal refers to the unpowered state. Actuating the solenoid will create the inverse state. In cases where solenoid function is proportional, the change in states may happen in degrees.
2. Poppet or Spool
Poppet valves utilize a passage cover which is held in place by a spring or the pressure of the medium flowing through the valve. The solenoid alters the position of the poppet either directly or by use of a pilot (described below), which opens or closes the passage. Poppet valves allow for higher flow rates but actuation force of the solenoid must be higher than in spool valves to accommodate for the pressures acting upon the poppet.
Spool type valves have seals along the bore of the spool. As the solenoid influences the position of the spool, the alignments of the seals change to stop or allow flow. Spool type valves have less surface area that is influenced by the pressure of the flow, so they can be actuated using less powerful solenoids. The drawback is that they also have a more limited flow rate.
Examples of Poppet and Spool Type Screw in Cartridge Valves for use with Hydraulic Solenoids
3. Direct or Pilot
Direct acting solenoids influence the flow of the medium by directly altering the position of the poppet or spool to open or close the valve. Direct acting valves are fast and have simpler design principles but are less capable in high flow applications.
Simplified Diagram of Closed and Open Direct Acting Solenoid Valves
Pilot operated solenoid valves have a poppet or diaphragm that is held closed by a spring and the differential pressure between the inlet and outlet ports. A smaller secondary channel links the inlet and outlet ports on either side of the poppet. The solenoid controls flow through this secondary channel, and when it is in the open state it allows a small amount of the medium to flow to the outlet port which begins to equalize the pressure acting on the poppet until it opens and allows for full flow. Pilot valves are slower than direct acting valves but allow for a smaller solenoid to control higher flow.
Simplified Diagram of Closed and Open Pilot Acting Solenoid Valves
4. 2, 3, or 4 Way Valve Function
Flow rate is controlled by a valve between the inlet and outlet port.
Most 3 way valves use 1 port as an inlet and 2 as outlets. The solenoid is used to direct inlet flow to the desired outlet port. 3 way valves can also use two ports as inlets and a single port as an outlet, to accomplish mixing functions.
A 4 way valve has 4 or 5 ports. There is 1 inlet, and 2 outlet ports much like a 3 way valve but whichever outlet port is off becomes a secondary inlet port that routes the flow to the final 1 or 2 exhaust ports. Some 4 way valves also have 3 way positioning. Instead of choosing between two paths of travel (2 way positioning) as shown in the diagram below, the solenoid is also capable of a third position that blocks all fluid from travelling through the valve to maintain the pressure in the loop.
Magnet-Schultz of America specializes in the custom engineering and manufacturing of solenoids, solenoid valves, electromagnets, voice coils, hydraulic tubes and coils, and locking devices. If you have any questions related to solenoid valve manufacturing or sourcing, you can contact us via email through the contact tab above or you can call us at 630.789.0600. We will be happy to assist in the development of your application.
Browse our past blogs for a more in-depth look at solenoid functions and subscribe to the notifications for future posts!