Indirect Acting Solenoid Valves
Indirect acting solenoid valves are more suited to process industry applications that always have media pressure in a pipeline. In a normally closed state, indirect solenoids operate by allowing a small amount of the process media into an orifice in the inlet port of the valve and into a chamber on top of the diaphragm. Under its own weight and volume, it applies pressure to the diaphragm, which is forced onto the valve seat and reinforcing it’s closed position.
When the solenoid coil is energised, the diaphragm lifts off the seat to open the valve, forcing the process media in the chamber back through the orifice in the inlet port and back into the flow stream, where it continues its journey through the valve and down the pipework. An indirect solenoid valve can also be referred to as a pilot operated solenoid valve, or pilot assist solenoid valve, as the process media acts as a pilot for the valve operation.
The fact that the process media acts as a pilot for operation means that indirect acting solenoid valves have a lower power consumption than direct acting valves, increasing efficiency. They are also more cost effective and occasionally more compact in their design. Indirect solenoids are available in a range of body and seal materials to suit almost any process industry application.
Indirect solenoid valves use the differential pressure of the media over the valve ports in order to open and close. Often, indirect solenoids require a minimum differential pressure of 0.5 bar to operate efficiently in the environment. However, this may vary depending on the brand of valve. Indirect acting solenoid valves operate through a rubber membrane, often called a diaphragm, which separates inlet and outlet ports. The diaphragm contains a small hole which allows media to flow to the upper compartment. Above the membrane, there is a spring which ensures the valve remains closed. When the valve is energised, the pilot orifice is opened, causing the pressure above the membrane to drop. The pressure difference on both sides of the membrane means the diaphragm is lifted and media can flow from the inlet port to the outlet port.
Indirect solenoid valves can only be used for one flow direction, due to the structure of the valves. Indirect acting solenoid valves are often used in applications where there is a sufficient pressure differential and a high desired flow rate. Common applications can include irrigation and car wash systems. However, depending on the material selection and operation of an indirect solenoid, they can often operate in hazardous areas, with either air, gas or water.