Quote Originally Posted by monkey spanners View Post
By my understanding no flow takes place down the equalising line, its just used to give evaporator outlet pressure to one side of the bellows in the valve, which acts with the spring (and superheat screw) against the pressure on the other side of the bellows provided by the phial.

Jon
As you say, the equalizer pressure balances against the phial pressure, with the diaphram in between them. The resulting pressure is transferred to the valve by a shaft on the equalized side.

The shaft has a seal where it goes through the valve wall. Those seals sometimes leak. This was common on older valves, but shaft seal materials are much better nowadays.