There is no need for a check valve if you have a ball valve between the vacuum former and your vacuum pump. You may choose to replace your ball valve with a check valve to avoid having to constantly throw the lever on the ball valve. Any check valves in a vacuum system should be located as close to the vacuum pump as possible. Also keep in mind that check valves almost always act as a restriction if they are not sized and tuned correctly to the system they are in. The “crack pressure” must be calculated correctly to insure correct usage. We include a check valve in the optional VSS kit that we sell which has been correctly sized to the Robinair #15800 8 CFM Vacuum pump. We do not rely on a PVC check valve made for water supply systems nor do we glue the valve into place within another component. All check valves will eventually fail and should not be permanently glued into the system. You do not want to have to destroy the whole system just to replace a faulty check valve. Your vacuum pump contains a separate check valve inside it. We will not tell you to remove the check valve that is in your vacuum pump. Removing the pump check valve allows oil to siphon up the vacuum tube, into the vacuum former and into other components reducing their service life and also voids the warranty on your vacuum pump. It also causes your vacuum pump to not be very efficient or pull a full vacuum because of the oil that is in the tube which should be in the bottom of the pump. The check valve we use is has been carefully selected as not to reduce efficiency or increase strain on your vacuum pump.