magnetic valve
A solenoid valve is a valve that is operated by an electromagnet . Depending on the design, these valves can switch very quickly. Solenoid valves with position detection can be operated as servo valves . The trend in industry is towards low voltages (24 V DC ) and low power through pilot control of the valves.
Control types
Depending on their operating mode, valves can be divided into the categories listed below.
Direct operated valves
Valves of this type use an actuator with an electromagnet; the drive is directly connected to the sealing element, the valve piston. When the electromagnet is switched off, a compression spring keeps the valve closed by pressing the valve piston against the valve seat. The direction of flow of the medium through the valve is specified in such a way that when the valve is closed, the differential pressure building up between the inlet and outlet of the valve also presses the valve piston against the valve seat . To open the valve, the piston must be lifted from the valve seat by the electromagnetic drive alone ; the drive must therefore work against the compression spring and against the differential pressure applied to the valve piston. The minimum force required by the electromagnetic drive to open the valve depends primarily on the spring force, the valve seat size and the maximum differential pressure when the valve is closed.
Pilot operated valves
Valves of this type require a pressure difference of the operating pressure to open and close. The minimum pressure required for this is specified as the minimum pressure in the technical data sheet. The drive only fulfills a pilot function here, relieving the main sealing element (diaphragm or piston). The medium pressure or the existing pressure difference lifts the main seal. With this type of control, small magnets can be used to control high pressures with large nominal sizes. Application example : Such pilot-operated valves are used in heating systems to temporarily switch the hot water flow from the heating circuit to a hot water boiler in order to heat it up, e.g. B. in Junkers' older CL 100 condensing boiler.
Force-controlled valves
Valves of this type are a combination of pilot operated and direct operated valves. They switch on from 0 bar and can also be used where direct operated valves are used. However, beyond their area of application, they are supplied with smaller magnets for higher pressures and larger nominal sizes. The drive opens a pilot bore and then lifts the sealing element from the main seat either directly or with the aid of the differential pressure between the inlet and outlet. The special feature of this control is that the drive can open and close the valve without the support of the differential pressure between the inlet and outlet.
Pressure controlled valves
Valves of this type are controlled by an externally used pilot valve. As a result, they can be controlled with a clean control medium, high temperatures, high pressures, contaminated media, aggressive equipment, etc.