With various aspects of servicing, maintenance, including driver assisted features and vehicle monitoring. For our 1996 Rover 200 and the 04 ZR 120+
The purge valve an electrically operated solenoid collects fuel vapors from the fuel tank and stores them in the charcoal canister, fuel vapors are then moved from the charcoal canister to the fuel injector then burned off inside the engine, The purge valve flow is monitored with sensors to determine a precise amount, helping in some way with the vehicles emissions.
Shown located on top of the charcoal canister. The canister is fixed into a metal bracket containing an isolation rubber on the bulkhead, bad condition of the rubber, could well be a contributing factor on how annoying the audible purge valve noise can sound in the cabin.
A damaged fuel filler cap seal wont create much of a vacuum within the fuel tank, so forcing the valve to activate for longer periods when maybe its not always required to do so. The valve is just clipped onto the top of the charcoal canister, with an option to test and try others.
The tapping sound given off by the purge valve, can initially be mistaken for sounding like the fuel injectors clicking, high tension leads arcing, or even the sound of a slack tappet giving an obvious cause for concern. However the tapping sound on some purge valves, are nothing more than a nuisance, and should just about be audible for short periods, but not consistant, as fumes are purged from the charcoal canister.
Information supplied is referenced only to our own 1996 Rover 200 Series, and 2004 MG-ZR 120+