I looked back at the other post to see what kind of Vac pump you have. I dont think it has a built in valve to valve off the vacuum. You will need to install an in line valve between the vac pump and the hose. like this
http://www.yellowjacket.com/HVACRPro...&l=4&c=28&p=87

A vacuum pump is not designed to hold a vacuum once it is turned off, in fact it will let the pumps oil be pulled into the charging hoses.