For the floor pump and frame pumps, place the valve at the top of the wheel pointing down. Open the screw all the way and make sure it is not stuck (quick push in). Push the brass chuck all the way on (past the smaller cap threads). That holds the check valve in the stem in. To preserve the seal in the chuck some riders use smooth wall valve stems. I have had my Silcas for 42 years (wife and I each have a frame pump and we have a floor pump) with threaded valves stems and it still seals well. The correct way to remove it is to wrap your thumb and forefinger around the chuck and use your other hand to strike your hand sharply. It will pop right off with no loss of pressure. I push it straight on and push it (or pull it at times) straight off with the chuck only, no screwing or wiggling. I have never had to replace a chuck seal, but I do have a spare for the floor and one for the frame mount..
Most people are not pushing the chuck far enough onto the stem, and are wiggling it to get it off. THe wiggling makes the threads cut the seal eventually. I also remember someting about the seal having a cone shaped hole and the narrow side should face away from the rim, serving to grasp the stem better.
With the old plastic body frame pump it is similar. Valve stem at the top, push the chuck all the way on. When done, hold the metal grip area with your hand as close to the chuck as possible, and strike you hand STRAIGHT down.
I use threaded and nutted 42mm valve stems. When I push the chuck on little of the stem is visible. I can easily get 105 pounds and have gotten 125 for tubulars (way back). I usually ride 95 pounds. The Silca system to me is far superior to the lever chuck systems and pumps. I greatly prefer it to the Zefal, as it is easier.
Last edited by Bill in VA; 04-22-19 at 08:46 PM.