Solenoid valves are ascendancy units which, if electrically activated or de-energized, either shut off or acquiesce aqueous or gas flow. The actuator takes the anatomy of an electromagnet. If energized, a alluring acreage builds up which pulls a agent or pivoted armature adjoin the activity of a spring. The agent solenoid valves is mechanically affiliated to a automated valve central the solenoid valve. If de-energized, the plunger or pivoted armature is alternate to its aboriginal position by the bounce activity and the valve allotment to its comatose state.
 
Solenoid valves come in various configurations and sizes. According to the mode of actuation, a distinction is made between direct-acting valves, internally piloted valves, and externally piloted valves. A further distinguishing feature is the number of port connections or the number of flow paths ("ways"). A two way solenoid valve has two ports and can be normally open or normally closed. A normally open solenoid valve allows a liquid or gas to flow through unless a current is applied to the solenoid VALVES. A normally closed valve works in the opposite manner. A three way solenoid valve has three ports; one port is common, one is normally open and the third is normally closed.
Laboratory automation makes frequent use of solenoid valves. The system controller can send an electrical signal (usually low voltage DC for small valves) to actuate the solenoid. In the case of a two-way VALVES, actuation can allow liquid to flow, and then remove the signal will close the solenoid valve and stop the flow of liquid. A gripper for grasping items on a device can be an air controlled device, powered by a solenoid valve to allow air pressure to close the gripper, and a second solenoid valve to open the gripper. If a three way solenoid valve is used, two separate valves are not needed. Three way valves are often used in basic liquid handling syringe pumps, to change the valve in between "fill" and "dispense" positions.