The extra pressure chamber above the membrane acts like an amplifier, so with a small solenoid still a large flow rate can be controlled. Because of the pressure difference on both sides of the membrane, the membrane will be lifted and the medium can flow from inlet port to outlet port. When the solenoid is energized, the pilot orifice is opened, which causes the pressure above the membrane to drop. The diameter of this “pilot” orifice is larger than the diameter of the hole in the membrane. This connection is blocked in the closed position by a solenoid. The chamber above the membrane is connected by a small channel to the low pressure port. The pressure and supporting spring above the membrane will ensure that the valve remains closed. The membrane has a small hole so that the medium can flow to the upper compartment. The inlet and outlet are separated by a rubber membrane, also called diaphragm. Usually these valves need a minimum pressure differential of around 0.5 bar. Indirect operated solenoid valves (also called servo operated, or pilot operated) use the differential pressure of the medium over the valve ports to open and close. Indirect Operated (Servo Or Pilot Operated) solenoid valves: The displayed solenoid valve is a direct operated, normally closed 2/2 way valve. This principle is therefore used for relatively small flow rates.ĭirect operated solenoid valves require no minimum operating pressure or pressure difference, so they can be used from 0 bar up to the maximum allowable pressure. The maximum operating pressure and the flow rate are directly related to the orifice diameter and the magnetic force of the solenoid valve. When the solenoid is actuated, the orifice will be closed.
This is called a Normally Closed (NC) valve.Ī Normally Open (NO) valve works the opposite way: it has a different construction so that the orifice is open when the solenoid is not powered. This opens the orifice so that the medium can flow through. An electric coil is positioned around the plunger.Īs soon as the coil is electrical energized, a magnetic field is created which pulls the plunger up towards the center of the coil. The plunger is made of a ferromagnetic material. The medium flows through a small orifice which can be closed off by a plunger with a rubber gasket on the bottom.Ī small spring holds the plunger down to close the valve. Direct operated solenoid valves:ĭirect operated (direct acting) solenoid valves have the most simple working principle. Solenoid valves can be categorized into different groups of operation. For more information about valve symbols and circuit functions, please visit the page about valve symbols. The examples show a 2/2-way Normally Open (NO) valve, a 2/2-way Normally Closed (NC) valve and a 3/2-way Normally Closed valve. The arrows in the box show the flow direction between the valve ports. The circuit function of a valve is symbolized in two rectangular boxes for the de-energized state (right side, visualized by ) and energized state (left). Below are some examples of the most common circuit functions. The circuit function can be expressed in a symbol.
More ports or combinations of valves in a single construction are possible. 3/2 way valves can have different functions such as normally closed, normally open, diverting or universal.
A 2/2 way valve can be ‘normally closed’ (closed in de-energized state) or ‘normally open’ (open in de-energized state).Ī 3/2 way valve has three ports and two positions and can therefore switch between two circuits. The specific purpose of a solenoid valve is expressed by its circuit function.Ī 2/2 way valve has two ports (inlet and outlet) and two positions (open or closed). Solenoid valves are used to close, dose, distribute or mix the flow of gas or liquid in a pipe.
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How to fix p2635.“A solenoid valve is an electromechanical actuated valve to control the flow of liquids and gases.” Circuit Functions of Solenoid Valves.