While the Silca pump I just got looks nice, and appears to be well made, I have never, in my 25 year "cycling carrier" have had so much freaking trouble trying to put air in my tires!!! (Well, except for that time many years ago when I tried another Silca pump.) There've been times it literally took me 5 MINUTES to get a tire to the proper pressure. Either the chuck blows off right after putting it on -- or just after I begin to pump it -- or nearly all the air comes out of the tire before I finally manage to get it to stay on. I seem to have a bit less trouble if I twist/screw the chuck on, though the instructions say to put it straight on (for a presta valve). Is there some special secret trick to getting this thing to work? Or is this just something that takes time to get the hang of?

Assuming you have the traditional old school push on brass Silca pump head, screw it on and off is a good practice as it stresses the valve stem at the tube less. Been using mine since new in 1986 and this is how I have always done it. Works without trouble.

The air that hisses out when "unscrewing" it is the air in the hose and chamber, not the tube. At least that has been my experience.

Frame pump or track pump?
Regardless, rotate the Presta valve to where you can get a solid connector for the chuck (usually Up on a frame pump) and release "a bit" of pressure to clear the valve, seat the chuck and have at it.
Keep a firm level head on a frame pump with the off-hand, on a track pump give it the willie.

Many/almost-all of these devices are decades old and require proper maintenance of the chuck seal and/or leather plunger.
These are still available OEM, just ask how/what:

https://silca.cc/pages/contact

Yeah, I got a new one (floor pump) recently after reading a glowing review from Road Bike Rider, and am very disappointed. Seems like it should be easy, and is anything but. Really gotta futz with it.

I have a buddy who has an old one he swears by, and he will check out my new one for me soon. If I learn anything, I'll report back.

P/V stems have a smooth band between the 2 threaded portions .. with a Bell shaped Silca pump head,
that is where the rubber gasket seals ..

Don't shove it on too far or ir will be hard to remove + you wear out the rubber seal ..I then it will blow off ..





...

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.

Glad I'm not alone. I got a Silca Pista pump for 5 bucks at St. Vinny's, and replaced the rubber seal in the head. The old seal was noticeably reamed out. It's pretty futzy. I'll try some of the suggestions given here. It would be nice to get a classic old pump working.

Note in edit: I probably wasn't pushing it on far enough. Thanks for the tip. Also, a bit of spit helps it slide on further.

Occasionally, back pressure would develop on these while pumping and the handle/piston would come out. Back in the 80s, a lady friend of mine was using one one time when it "backfired" and rocketed into the side of an old Toyota and dented it.

Get tubes that have smooth valve stems instead of threaded.

That is true. Thanks for mentioning that. I did notice that I had misworded my first post. I have edited it here in my quote above. You want to push it on to just before it holds the check valve open. If you get handle push back (not resistance, but push back) you have gone a bit too far. You will not feel it until the pressure gets up. With the frame pump, I have found that it is easier to totally remove and re-attach it, than to try moving a millimeter or so out. The floor pump and large brass chuck is s bit easier to move a small amount.