Never was crazy about the chuck that came on the Silca pump I got a while back (losing air while putting it on and off, chuck blowing off, etc.). Recently found out about the Hiro chuck, figured that would be better, but it seems to be much WORSE! Only way I found to get the chuck on and off without losing half the air from the tire is to leave the lever closed all the time. Is that the way its supposed to work? (I thought the lever should be open when putting it on and off.)

This may help. I have to ask. Are you sure the air coming out when you release the chuck is not just the air left in the pump hose? Very common to hear a big ssssttttt coming from the pump when releasing the chuck.

I'm ABSOLUTELY certain its not the air coming out of the hose, because the tire is almost FLAT after that (about 20 psi left in it).

Years ago I switched to unthreaded valve stems to use with my Silva pump. I found that the threaded stems just chewed up the chuck seal, while there was enough grip on the smooth stem to hold the chuck in place at the pressures I used (100-110 psi). There aren’t many tires with 50-60mm smooth stems, but they’re out there, and the chuck seal lasts for years.

FYI, the modern urethane pump gaskets hold up to threaded stems better than the traditional butyl rubber gaskets.

When you use the Hiro chuck, do you shove it down hard enough to depress the presta valve? If so, you’re doing it wrong. I unscrew the valve, open the chuck, slide until the threads give a little resistance, then close the chuck. The air pressure when you pump breaks the seal (which is only held by air pressure in the tube), unlike a Schrader valve where the chuck has to overcome spring force.

+1. This is the way to use it. I bought a Hero chuck in 2010 as an aftermarket replacement for the OEM chuck on my Park PFP-4 floor pump. The chuck was ridiculously expensive ($75!) but worth every cent. It has been flawless in daily use requiring only one replacement gasket in all that time. As noted, just push the chuck onto the valve stem until it seats on the threads and close the side lever. Adjust the required force to close the lever by threading the end cap looser or tighter to get a good seal but not needing excessive closing force.

Spot on advice, for way too long was pressing down too hard, realised this error recently and now its so much more straightforward (cue slaps head emoji)

Recently splurged and bought the Silca floor pump with Hiro head and compared it to my old Specialized pump with rubber hose and flip chuck that does have to be pushed on the valve firmly - I was disappointed with the Silca pump that I received - foot base was very hard to attach , not a fan of the stiff braided hose , was as difficult as the Specialized getting from 90 to 100 lbs , and had to think too much in placing the Hiro on the valve otherwise the spokes prevented closure of the lever - I had seen the video and so I knew not to push the chuck down too much.

I returned the pump to Silca but unfortunately their policy only provides store credit - and so my old pump is Ok for now but I'm thinking of getting a compressor and like the Park head but an alternative would be the Hirame head which looks to be designed similar to my Specialized .

Other than cosmetic, I can't see any difference between the Hiro and Hirame.

I was wrong , took another look at the demo video for both , think I was opening the lever too far before attaching to the valve - other responders pointed OP to the solution of the issue - in my case I proved that it wasn't rational to get a new pump after checking out the Silca , a mistake .