As 3/2-way valves have 3 connections, they offer a much wider range of functions than 2/2-way valves and are suitable for implementing NC, NO, mixing and distribution functions, as illustrated in the following diagram. The different feature is always the assignment of the connections, which is different for each function. In order to implement these different functions, the internal springs of the solenoid valves and the appropriate solenoid coil must be selected accordingly.

  1. The design as an NC valve requires a strong external core spring to ensure that the body nozzle is sealed, as the pressure in the body nozzle is below the plunger. The strength of the internal spring is not very important, as the pressure helps to close the nozzle in the pole when actuated. The solenoid coil must be strong enough so that the valve can pull the plunger to the pole against the spring force of the external spring without the help of the operating pressure at the inlet.
  2. In the NO valve design, the spring force of the external plunger spring is less important, as the pressure at the inlet helps to close the body nozzle. This spring is thus usually configurated with a comparatively low spring force. However, the internal core spring must be strong enough to ensure that the inlet on the guide tube is reliably closed despite the pressure when the plunger is attracted to the pole. The solenoid coil must be strong enough to ensure that the plunger of the solenoid valve is pulled to the pole when actuated against the inlet pressure.
  3. The mixing function requires internal and external core springs that reliably close the body and pole nozzle in the respective switching state against the pressure at the inlets. The solenoid coil must be strong enough to ensure that the solenoid plunger can be reliably actuated against the spring forces.
  4. To achieve the distribution function, the external core spring must be strong enough so that the pole nozzle can be opened against the pressure applied from below. The pressure applied helps to close both the body nozzle and the pole nozzle, so that the internal plunger spring doesn’t have to be strong. The solenoid coil must be so strong that the plunger can be actuated against the force of the external plunger spring.
FunctionExternal plunger springInternal plunger spring
Mixing Functionstrongstrong
Distribution Functionstrongweak

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