The basic principle.
A solenoid turns an electrical command into mechanical force. In a hydraulic valve, this can move a closing element directly or control a small pilot passage that influences a larger stage.
The coil is only one part of the assembly. A command can be present while a mechanical or hydraulic condition prevents the expected result. Conversely, not every change in fluid behaviour is caused by the coil.
A pilot-controlled lowering path.
The controller energises a coil. A pilot passage changes pressure acting on a main element, which changes the larger flow path. This is a conceptual example, not a description of every lowering valve.
Follow the relationship.
- Electrical commandEnergises the coil.
- Mechanical responseMoves a plunger or pilot element.
- Hydraulic responseChanges a fluid path or pressure balance.
Connect it to the lift.
Normally open and normally closed describe specified rest conditions. Energising a valve does not universally mean opening it. The circuit diagram and manufacturer’s description establish what each coil and passage does.
A closer look
Proportional valves control force or opening over a range using appropriate electronics. They should not be modelled as ordinary on/off valves operating at arbitrary supply voltages.
Check your understanding
If the coil energises, is that proof that the main flow path has changed correctly?
Reveal the explanation
No. The actuator, pilot stage and main hydraulic element must all perform their intended functions.