Just make sure the seal is tight, no need to jab it in too hard. And always make sure the little chain is down there also, it reduces the risk of water superheating and the vac pot exploding.
Taken from an article written by Mark Prince on
Vac Pots:
"quote" In fact, one thing I want to bring up here... there's a reason why most cloth and paper filters for vac pots have that little metal chain at the bottom of them (with the bearings as "links"). Yes, so you can pull the spring on the filter, but also to provide a conductive area for water to boil in the bottom globe. water when it touches the metal will boil. Apparently when you don't use these kinds of filters and don't have those little metal balls in the bottom, you can effectively "superheat" the water without it converting in a timely manner into gas, and literally blow out your vac pot when the "flash boil" occurs. It was explained with much greater detail in the newsgroup alt.coffee, and chem labs have similar problems - often the culprit is a "too clean" vessel that won't induce boiling at its normal temperatures for your elevation. Chem labs use boiling stones. We use those little metal balls. "end quote"