There is a valve on the top of the vessel ( the same as a car tyre ) just pump it up to 1 bar but you will have to open the expansion relief valve and keep it open to drop the water pressure in the central heating system before you attempt it so that you are not pumping against the system pressure, the expansion vessel may be full of water so that has to be forced out as you are pumping air in,I have got a portable power station with a built in pump when i do expansion vessels on unvented hot water tanks it makes the job easier
toptrish, January 2015
