Assisted lift solenoid valves are a combination of a direct acting solenoid valve and a pressure assisted solenoid valve just that in this case the armature is now mechanically connected to a diaphragm typically by means of a spring, hence the term Assisted Lift Solenoid Valve. The principle here is that the armature assembly can assisted the diaphragm into the open position for low pressures and vacuum and have pressure assistance via internal pilot for higher pressures. This medium sized armature means a medium power coil is required to mechanically assist for low pressure applications with the added benefit of an internal pilot to give pressure assistance for higher working pressures.
Assisted lift / zero rated solenoid valves are often used for vacuum applications where operating with zero or close to zero pressure differential can be an important factor of the solenoid valves functionality. Its is due to these operating properties the assisted lift solenoid valve is often referred to as a Zero Pressure or Zero Rated solenoid valve.
Assisted lift solenoid valves that utilise a diaphragm valve within their functionality are often referred to as diaphragm solenoid valves or hung diaphragm valves. The diaphragm arrangement allows for an efficient solution with minimal moving parts that utilises the basic laws of physics for its functionality.
The picture on the right / below shows a large probably 11/2 or 2" threaded 2/2 normally closed assisted lift / hung diaphragm solenoid assisted lift solenoid valve. When the solenoid coil not energised (first picture) the armature rests down against the diaphragm and a central pilot hole, blocking the pilot hole and preventing the diaphragm from lifting. You can see the inlet port 1 media (blue) has found a path above above the diaphragm forcing it to seal downwards and the valve is closed.
The second picture on the right / below shows this kick pilot assisted lift solenoid valve in the energised open position. The electromagnetic coil has generated a magnetic field which in turn has lifted the central solenoid armature assembly in the tube surrounded by the magnet / coil, which has assisted the diaphragm into the open position with pilot pressure assistance
Pilot pressure assistance in basic terms are basically small holes allowing some flow of media, typically via a valve mechanism. In this case the valve diaphragm has two pilot holes, one larger central (outlet) and another smaller (Inlet) hole at some point to one side of the diaphragm. The principle here is that whatever media is entering the valve it will also travel through a "small" inlet hole at the edge and generate pressure above the diaphragm to pressure assist close.
In the valve closed state the media simply pushes the sealing diaphragm down against the sealing face as pressure tries to escape down the outlet port of the valve. When the solenoid valve opens the central "bigger outlet pilot" hole is exposed by the armature lifting towards to solenoid coil, the pressure above the diaphragm then escapes down this outlet pilot hole stream faster than it can be replenished by the "smaller inlet pilot hole", thus generating low pressure above the diaphragm and higher pressure under the diaphragm so effectively pushing the valve open.