specialmonkey

I used a floor pump at my LBS, it was silver, and said something like Air Tool on it, I think it might be made by Specialized (Googled it), I have a similar Specialized pump at home.

The Air Tool at the LBS I noticed when attaching the valve, did not lose any pressure from the tire, while my similar pump at home seems to always lose a little ... not a big deal but, I would prefer not to lose air on attaching.

I don't think I did anything differently, like fitting the nozzle more deeply over the valve ...

Is there anything to this? Can anyone recommend a pump that works this way.

Another thing I wondered, when detaching the nozzle, some air audibly escapes, is this accounted for in the gauge reading, or should I add more air, or is this a negligible amount?

Dyskolos

The air escaping on detaching is pressurized air in the hose and need not be accounted for.

fietsbob

One with a powered Compressor behind it..

Papa Tom

Is that right? All these years of biking and pumping tires and I never knew that. I always assumed it was air escaping the tire tube while the valve stem pin was still open. Can you confirm this, or am i just the last one on Earth who didn't know it already?

Dyskolos

I can only confirm it through logic and experience. Once pressure drops on the hose side, the valve closes preventing escape of air. Then, the pressure in the hose decreases to equal ambient pressure.

In a Presta valve, the valve is held open with air pressure, not mechanically as in a Schrader valve. Once the pressure decreases on the hose side, the valve closes. If that were not the case, the valve would leak pressure until the nut is closed to secure the valve closed.

To confirm this in your own experience, take a deflated tube, i.e., the pressure is equal on both sides of the valve, open the nut and push in the stem. Notice that it stays in. There is not a spring holding it closed, only air pressure when inflated.

cyccommute 

Not necessarily. If the valve is a presta and you are using a presta chuck, your statement is true. The presta valve is a check valve with one way flow. When the pressure in the tire exceeds the pressure in the hose, the valve seals and any air loss is just from the air in the hose.

Schrader valves (and some chucks on pumps do the same to presta), on the other hand, have to be held open to get air in the tire. Any air leakage is coming from the hose and the tire.

One caveat: A Schrader valve will act like a check valve but it has a high cracking pressure. Generally, it needs an extra 25 psi over the internal pressure to cause the valve to open. Of course that means that you are going to have 25 psi over what you wanted in your tire. It's just easier to hold the valve open but you do risk pressure loss if the seal between the valve and the air source isn't good.

SuperRecord

I second the hose air bleeding off. Try looking at the hose as you release the valve from the stem. The hose stiffness might change to limp when you release the valve stem. OMG

Dyskolos

That's a good point - I assumed Presta, which may not have been a good assumption.

Retro Grouch 

Schrader valve or Presta vakve?

A Schrader valve pump head has a little finger that opens the valve as it's attached to the valve stem. If you are using a hand pump that threads onto the valve stem, it's common to lose a little air pressure from the tire in the process of attaching the pump. That's the thing I like least about Schroeder valves. The thing I like most about Schrader valves is using an air compressor to inflate the tire because that chuck doesn't have to be threaded onto the valve stem. Zero air loss.

Presta valves tend to stick a little bit. When that happens it's real hard to push a hand pump hard enough to open the valve. I always "burp" the valve before attaching the pump. A little bit of air always escapes during that process.

Iride01 

If you have to rock your chuck back and forth to remove it, you might be knocking against the locking screw of the presta valve and releasing air. IMO, the chuck should pretty much release itself when you unlatch it. A small tug at most. The difference with the difficulty of removing an old chuck and the ease of removing the new chuck I replaced it with is very great. I didn't notice how bad it was till I started pulling valve stems out of my tubes.

specialmonkey

I'm mainly interested in pumps (I mostly use Presta) that won't cause the tube to lose air when attaching it to the valve.

I noticed this at the LBS, using the Air Tool pump, as I didn't hear air escape. I also noticed the gauge read close to the last pressure pumped into the tire on attaching.

On my Specialized pump (I just noticed it also says Air Tool), air normally leaks out a bit on attaching hose to valve, and the gauge usually reads 20 psi less than what was pumped last.

I'm not sure if I got lucky at the LBS; had the tube valve screwed out just enough; attached the pump to the valve more precisely; or if the LBS pump was somehow superior.

70sSanO

Bill in VA

Try this pump. It is a Silca Pista. https://www.universalcycles.com/shop...s.php?id=93237 It is for presta and has a push on fitting not a lever type.
I have an original that is now 40 years old. Back then the barrel tube was made of Columbus tubing. Parts are still available. and the guage is accurate. It will easily pump to 160lbs or more without a lot of pump strokes. I have never had an issue over the years.

The one above is a new version.

cny-bikeman

It is extremely unlikely that you will lose any appreciable pressure when attaching a pump - less than 1 lb. Specialized uses the Air Tool designation for all of their pumps https://www.specialized.com/us/en/equ.../pumps/c/pumps. Given the discussion of Presta vs. Shrader it would have been helpful to indicate which you have in your 2nd post.

cyccommute 

The very best pasta chuck is this one



It's a Silca chuck and, while a bit expensive, it will last for generations. Push it on, pull it off. It does seem to work better with longer stems, however.

Another alternative is this one


It's from SKS and much, much cheaper as well as smaller. It might not be generationally robust but it gets the job done.

I would suggest that you avoid any pump with a "universal head". The head is meant to squish down on the valve but it also depresses the stem so that it can hold a schrader valve open. Don't confuse that with the type of pump head with two holes.

cyccommute 

Again, it would depend on several factors. For a presta, there is little to no chance of having air leak out of the pump. But with schrader, the valve is held open so it fills the tube. For a high pressure tire, that could result in a significant pressure loss. And, in my experience, schrader valves tend to seal more poorly around the chuck so they leak more. Any leakage with a schrader is pressure being lost.

fietsbob

The Smooth band on a presta stem is where the pump head seal goes..

Charliekeet

Tundra_Man 

If you're hearing leaking when the head is attached and/or you're pumping air, then there's a chance that the pump head is worn. I get about five years out of mine before they start to leak a little bit.

The good news is, you don't have to throw away the whole floor pump. Replacement heads are available for less than $10 and it's a five minute job to swap them out.

As others have repeatedly said already, hearing air escaping the hose when the head is being removed is normal.

Dyskolos

Out of curiosity, I topped off my tubes and paid close attention to the experience. :-) Using a Serfas FP-200SE pump with a newly refreshed gasket on Michelin Airstop tubes (no threads), I heard the valve "pop" closed after pumping and releasing the lever. No air escaped until I removed the head from the valve.

AnkleWork

Another nonsense thread in an increasingly nonsense forum. What could it possibly matter if you lose a little air while attaching a pump as you are using the pump to add air anyway?!?