Pilot operated solenoid valves have two chambers that are separated by a diaphragm. Sometimes the diaphragm is not connected to the core and is know as indirect acting.
How do Pilot Operated Solenoid Valves work?
The upper chamber is connected to upstream through a pilot hole in either the cover or diaphragm. The media exerts a pressure that acts on the upper side of the diaphragm and keeps the valve closed. When the coil is charged the core lifts off the orifice seat allowing the operating chamber to de-pressurise. The thrust of the upstream pressure under the diaphragm continues, lifting the diaphragm and opening the valve.
Pilot operated solenoid valves only operate with a suitable upstream pressure differential and do not operate at zero pressure. Also a minimum pressure differential across the valve is required to keep them open or closed. Pilot operated solenoid valves can provide high flow rates at high pressures with lower power consumption
Applications of Two Way Pilot Operated Solenoid Valves
Two Way Pilot Operated Solenoid Valves are suitable for mains water supply as they provide high flow rate and mains water will supply sufficient pressure differentials to operate the valve. E.g. a water metering system.
Two Way Pilot Operated Solenoid Valves are useful in operations involving mains water systems where water hammer is a common problem as some M&M solenoid valves are fitted with an Anti Water Hammer device. An example of this is in an electronic mixer tap application.
In air compressor dump valves the large orifice and fast operating speed provides a quick dump time. Two Way Pilot Operated Solenoid Valves can be used with a pressure switch.
Two Way Pilot Operated Solenoid Valves are ideal for lubricating an oil system as they provide the oil at a sufficient pressure.
Water Meter Application
Water meters are electromechanical appliances allowing the supply of a specific amount of water to the equipment it controls. They are equipped with analog or digital readers. The water meter measures the amount of water flowing through it. A predefined rating is set by using a knot: when it is reached, the water meter sends an electric signal to the solenoid valve and stops the supply of liquid.
Applications vary and one of the most significant applications is in the food industry. For example bread making, the water meter is used to supply the exact amount of water needed when the dough is kneaded.
Pilot operated valves are suitable for this application due to the larger flow rate. When water is coming from a tank the pressure is very low and pilot operated solenoid valves with assisted lift should be used instead as they work with minimum working pressure equal to zero.
Electronic Mixer Tap Application
Electronic mixer taps are used in taps to supply water for washing of hands without having to touch the unit. There is an infrared area in front of the taps and when they sense movement water will flow. This application is compulsory in places where hygiene is critical such as hospitals and public bathrooms. This application also saves money as the flow is turned off after a few seconds, reducing consumption.
The system works by an optical sensor that produces an infrared beam of light. When the beam of light is interrupted by the presence of a hand the sensor sends an electrical impulse to the control unit which operates two solenoid valves. Each solenoid valve is connected to a hydraulic system one delivers hot and the other cold water. This mixture of hot and cold ensures that water temperature is properly regulated.
A compressor produces compressed air and consists of a piston compressor with power being supplied by an electric motor, a refrigerator and a tank. Air is taken from the atmosphere, compressed by the compressor and collected into a tank. A filter is fitted at the intake to prevent foreign particles from going into the cylinder head. A cooling coil removes the condensate created by heating of the compressed air.
In an operating system the compressor is powered by an electric motor which brings in air, compresses it and sends it to the refrigerator and then to the tank. During this process the solenoid valves is energised and closes the circuit keeping it under pressure. When the desired pressure reading is reached in the tank a pressure switch stops the motor and the check valve keeps air inside the tank. The solenoid valve can be de-energised to allow exceeding air still in the circuit to be exhausted this prevents the compressor from remaining under pressure for too long and getting damaged.
Two Way Pilot Operated Solenoid Valves with Assisted Lift work similarly to pilot operated solenoid valves but the diaphragm is coupled to the moving core. At low pressures when the coil is energised the diaphragm is lifted directly by the moving core. At higher pressures the diaphragm is assisted by the internal pressure in the valve. These valves can operate at zero pressure differential but are not available in the normally open configuration.
Applications of Two Way Pilot Operated Solenoid Valves with Assisted Lift
These valves can be used for diesel fuel supply. Generally diesel is supplied from a header tank, meaning that the fuel may not be at a sufficient pressure to operate a standard pilot operated valve so an assisted lift pilot operated valve can be used. The use of viton seals is recommended for this application. Two Way Pilot Operated Solenoid Valves with Assisted Lift can also be used in Low pressure water systems, or in systems where pressures fluctuate and may drop to zero. Also systems where back pressure may increase causing a very low pressure differential across the valve an assisted lift valve can be used as it does not require a pressure differential to operate. An assisted lift valve is often suitable for vacuum applications, for example in a vacuum packing machine.
Vacuum Packing Application
An example of an application using two way solenoid valves with assisted lift is with the machine used for vacuum packing food goods in places such as supermarkets, butchers and catering services. Many food items are vacuum packed to prolong shelf life. The vacuum packer lets an inert gas with a small amount of oxygen into the package which modifies the conditions of the atmosphere so food perishes more slowly. At the end of the operation the vacuum packer seals the plastic bag.
How can a solenoid valve be used in this application?
Food items inside the plastic bags are blocked under a transparent bell. The bell is lowered and the vacuum process is started by the switch of a button. Air is sucked up by the pump and a vacuum is generated. The plastic bag sticks to the product and is sealed. After which the atmospheric pressure in the packing chamber is restored and the bell is opened. Two solenoid valves can be used to control the vacuum cycle. One lets the pump suck up air from the chamber and keep vacuum in the room when the sucking is over. The other restores the atmospheric pressure after the package has been sealed.
For more advice and information on how M&M International solenoid valves can be used in your application, please contact our technical team on +44 (0) 8444 501123.