Thanks NortonDommi

The bushings were my first impregnation, the chamber was primarilyp used to degass liquid silicone rubbers and resins prior to casting,

The pump is a 240v 30cfm jobby, normally used for changing the gas in air conditioning units. I acquired it from eBay for cheap, but its a little undersized for my 12" x 12" chamber, I could do with a 60cfm unit to halve the time it takes to get to a decent negative pressure (resin degasses at around -25, silicone needs -28 or more).