3 Types of Solenoid Valve Construction: Spool, Poppet, and Rotary

By definition, solenoid valves, for pneumatic use, have a solenoid coil which when electralised effects some consequence. The consequence varies between the different types of solenoid valve constructions: Spool, Poppet and Rotary.

1. Solenoid Spool Valve

Spool valves are the most common type of solenoid In the case of Spool valves, when the solenoid coil is electralised, a magnetic field is produced and the internal spool physically moves within the valve body. Since there are small grooves on the spool (whereby raised areas are called 'lands'), a change in the position of the spool within the valve body, changes the paths in which compressed air can flow. When the solenoid coil is no longer electralised, spools often return to their original position due to a spring or some other means.

2. Solenoid Poppet Valves

A poppet solenoid valve works in a similar fashion. However, instead of a spool, a poppet (usually a metallic ball) changes position, thereby changing the airways. When the solenoid is electralised, the plunger is pulled upwards (against the spring), so that the outlet orifice is opened. When the solenoid is not electralised, the plunger returns to its default position with the help of a spring.

Poppet valves are incredibly low maintenance and are incredibly robust; however, they often come at a higher cost due to the additional manufacturing processes that are required to produce them. One other point to note is that poppet valves are only common in pneumatic valves (not hydraulic valves) due to the high amount of force required to displace a poppet.

Figure 2. Solenoid Poppet Valve

3. Solenoid Rotary Valve

Rotary solenoid valves consist of a rotating spool which can align in such a way as to determine the possible paths of compressed air. Rotary solenoid valves are uncommon in general industry; the majority of rotary valves are hand operated. They are more common in hydraulics and are seldomly found in pneumatics.