The main difference between direct acting and pilot solenoids is that direct-acting solenoid valves have a direct connection with the opening and closing armature, whereas pilot-operated valves employ the use of the process fluid to assist in piloting the operation of the valve. Both types of solenoid valve have their particular merits, which we will explore in greater detail here.
Direct acting solenoid valves
Direct acting solenoids adhere to simple working principles. They do not use a diaphragm – their seal is part of the moving core – and they will remain closed even when no pressure is being applied. This is in contrast to a pilot operated valve, which requires some pressure for the valve to stay closed. The main components of a direct-acting 2-way plunger valve, such as the Type 6013, are a coil, a closing spring, a valve body cover and the valve body with the seat.
In a normally closed direct acting solenoid valve, the path to the outlet port is blocked when no current is applied to the coil as the closing spring presses the plunger onto the valve seat. Current through the coil generates a starting force, which pulls the plunger and the seal against the spring force, and draws the medium upward. As such, the channel is opened for the medium to flow through the direct acting valve.
Cost-effective direct-acting 2-way plunger valves are used in universal applications for neutral and clean liquids, gases and vapours. Versions with special high-quality materials also allow for use in mildly acidic and alkaline solutions. They can therefore be used for a broad spectrum of applications, such as shut-off, dosing, filling and ventilation. Due to a spring-damped seat seal, these valve types have a long service life, as well as increased switching cycles and service life due to sliding ring bearings.
Benefits of direct acting solenoid valves
- Suitable for negative pressure circuits.
- Designed to cope with particle debris.
- Available in very cost-effective compact sizes.
- 2/2 and 3/2 way normally open or normally closed versions.
- Miniature versions available for very high pressures.
Pilot operated solenoid valves
Pilot solenoid valves use the differential pressure of the medium over the valve ports to open and close. Also known as servo-assisted solenoids, these valves provide high flow rates and can operate at higher pressure and temperature ranges, with lower power consumption. A servo-assisted, diaphragm solenoid valve with pilot control employs the use of a small chamber directly above the diaphragm to assist in the operation of the valve. Process fluid is allowed to enter the chamber through a small orifice in the inlet port, and in a normally closed valve, compresses against the diaphragm and forces is against the seat to maintain the closing seal.
Once current is applied to the pilot solenoid, the diaphragm is pulled upwards against the spring pressure, and the pilot fluid in the chamber is forced back through the orifice in the inlet port where it re-joins the main flow through the valve body.
The main areas of application for pilot-controlled diaphragm solenoid valves are liquid or gaseous media (such as compressed air, water and hydraulic oils) within closed circuits in which little or no differential pressure is present for opening and closing. The Type 290 features a soft-kick function for a longer service life and all of the DC versions feature energy-saving power reduction. The Type 6213 EV, on the other hand, uses a spring as a coupling for ‘diaphragm-friendly’ opening of the main seat in frequent working cycles.
Benefits of Pilot solenoid valves
- Excellent for very large flow.
- Pressure assists valve operation.
- Needs minimum pressure differential.
- More economical for higher flow values
- Lower electrical power level.
Direct and pilot operated solenoids from Bürkert
Bürkert has been developing and producing solenoid valves for more than 70 years. In doing so, we use cutting edge technical principles and innovative technologies with a common goal: to fulfil your requirements. We customise our valves to fit your applications and therefore offer you the optimal solution for your needs.
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