What are direct-acting solenoid valves?
Direct-acting solenoid valves adhere to simple working principles. They don’t use a diaphragm as their seal is part of the moving core and will remain closed even when no pressure is being applied. This is in contrast to a pilot-operated valve which requires pressure for the valve to stay closed. The main components of a direct-acting two-way plunger valve 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 passing through the coil generates a starting force which pulls the plunger and the seal against the spring force. This draws the medium upward. As a result, the channel is opened for the medium to flow through.
Cost-effective direct-acting two-way plunger valves are used in universal applications for neutral and clean liquids, vapours and gases. Versions with special high-quality materials also allow for use in mildly acidic and alkaline solutions. They can be used for a broad range 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 due to sliding ring bearings.
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.
What are the benefits of direct-acting solenoid valves?
So, what advantages can you gain from using a direct-acting solenoid valve?
- Suitable for negative pressure circuits
- Designed to cope with particle debris
- Available in cost-effective compact sizes
- 2/2 and 3/2 normally open or normally closed versions
- Miniature versions are available for very high pressures
What are pilot-operated solenoid valves?
Pilot-operated 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 enters the chamber through a small orifice in the inlet port and, in a normally closed valve, compresses against the diaphragm and forces it against the seat to maintain the closing seal.
Once current is applied to the pilot-operated solenoid, the diaphragm is pulled upwards against the spring pressure. The pilot fluid in the chamber is then 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, or within closed circuits in which little or no differential pressure is present for opening and closing.
So, what advantages can you gain from using a pilot-operated solenoid valve?
- Excellent for very large flow
- Pressure assists valve operation
- Needs a minimum pressure differential
- More economical for higher flow values
- Lower electrical power level
Direct-acting vs pilot-operated solenoid valve
The main difference between direct-acting and pilot-operating solenoid valves is that the former have a direct connection with the opening and closing armature. In comparison, pilot-operated solenoids employ the use of the process fluid to assist in piloting the operation of the valve.
Solenoid valves at Bürkert
Check out our range of solenoid valves, including the Type 6013, on our website. We have a wide variety of pilot-operated and direct-acting solenoid valves to choose from.
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