all you need is a tyre press gauge & a bicycle pump, when press is zero pump vessel to 1/2bar(7-8 psi) then pressurise system from cold feed to 1bar. job done. but if you have water coming out of the air valve when you depress it, your expansion vessel is kaput & needs to be replaced. you MUST also put some more corrosion inhibitor in the system. No dont ask me, its too complicated for the layman.
a heating engineer, December 2009