These are used for food canning,for resin work the hole must be sealed or it would pop at about 20psi.The dial says 30,but I've put 50,more than enough to burst any bubbles in the mix.
I have and use the Tap Plastics unit.This is my pressure pot,one is on sale at Amazon.it is made by All American Canning #921.Seal the pop off valve hole with silicone,add a quick release fitting and your good to go.Been casting with these for over 12 years now.