I have this chuck on a Silca pump, and it took a while to figure out how to set it up. You do this by turning the adjusting ring that holds the red rubber gasket in whatever direction you need until the closed chuck holds the valve stem securely. Once this is done it works great.
Chuck will not stay locked and needs to be held in place with one hand while pumping with the other. Worse than cheapest Zefal floor pump chuck. Tried to reach customer service without response. Total waste of money. PS - I am former racer and mechanic who has 40+ years experience with pumping tires.
I love this chuck! I attached it to my Milwaukee 12v cordless inflator and it's pure magic topping of my tubeless tires before a ride. It never leaks air, is always easy to attach and just plain works time after time. Only downside is the cost but I'm sure I'll be using this for years.
Sure you can find a presta pump head for less, but this is true quality that will last a lifetime. The lever action allows you to seal the valve and inflate your tires without worrying about it slipping off or needing to hold it in place. It is quick, easy and sturdy.
Im a big believer in quality. I know some would consider this expensive. But I will say very well made and moron proof. By that I mean Im not the best with gadgets sometimes and yet I had no problem using product. This product is worth the investment because you will pass it down as it will outlast you.
I use it on my go to pump. I run my tires from 60 to 90 psi so I don't know about how well the head stays on when using at high pressures. I like that I'm not twisting my presta valve when I put it on or off. It goes on quick and holds well. It's down fall is price and size. The size is OK on a floor pump, but if you carry it it's kind of big.
I had purchased a Silca pump a couple of years ago but had seldom used it as there was one problem after another with it. Threaded valve stems wore out the rubber gasket very quickly so I bought replacements. It didn't want to seal very well on any valve stems whether threaded or smooth. Also, the hose fitting came apart but I contacted Silca and they replaced the hose as it was under warranty. I thought maybe the locking valve chuck would solve all of the problems and allow me to finally get some use of this expensive pump instead of continuing to use my good old reliable $50 pump from brand S. Well, it just turned into throwing good money after bad as the chuck, when locked, does not stay on the valve when the pressure nears a usable pressure, 95 to 100 psi. Silca seems to make very attractive and very expensive products, but from my experience, they just don't work very well. Very disappointing!