Tandem Tom

When I use the pump on Presta valves it does not seem to depress the valve vey well. It did not do this in the past. So I tried letting the air out of the tire then start pumping and this seems to work.
Any thoughts?

10 Wheels

Normal for most riders.

billDennen

Likely the valve and not the pump. I have one that sticks (out of 6), so -- like you -- I manually release pressure before pumping up to specifications.

HillRider

The pump head isn't supposed to depress the valve stem in a Presta valve, it opens strictly on the pressure differential. However, many (most?) Presta valves will be a bit sticky when the nut is loosened and it takes a large amount of overpressure to open it the first time. The standard cure is to "burp" the valve after you loosen the nut by tapping the stem to get it to puff out a small amount of air and relieve the seat sticking. Then inflate to full pressure.

jon c. 

I will never understand the supposed advantage of Presta valves. But I grudgingly live with them.

LesterOfPuppets

For general use valve type is a tossup for me. In the shop I like presta way better. Hate needing a tool to deflate tires.

Im with hillrider,OP. Just tap the valve before attaching pump.

HillRider

Advantages: Lighter, require a smaller hole in the rim, deflate when required with only finger pressure.
Disadvantages: Require a specific pump head or require an adapter to use common pumps, compressors or gas station hoses, fragile if side-loaded.

Yep, we're stuck with them.

FBinNY 

Today I'd say most, however this was NEVER a problem years ago when the valves were made in Italy. It seems that the Taiwanese versions use a softer material for the seal (or have a different seat angle) and the current stuff sticks pretty badly after being closed a while. BTW- it doesn't matter if you tighten the nut or not, it's a question of pressure and time.

Another example of a new problem on something that worked for almost a century.

Vince Canepa

I have a Joe Blow Pro and it DOES press down the Presta stem when I move the locking lever if you insert the valve far enough into the chuck. Perhaps something inside the chuck is worn.

HillRider

Well, it wasn't designed to do that but the long stems on many current Presta tubes probably go deeper into the head than expected and the inner stem hits the far side and is depressed.

FBinNY 

Depressing the valve defeats the design of the Presta valve entirely. The beauty of the PV design (when it works) is that it's a simple check valve. Air pressure outside opens the valve and air flows in. Air pressure inside closes the valve, so no air is lost when pumps are removed. These valves were used very effectively for many decades with simple pumps having no thumb lock or internal check valves, ie. Silca hand pumps.

Looigi

Correct. The tire valve serves as the inflation check valve and prevents air loss in the hose/pump and when the hose is removed. This gets more important for high pressure, low volume tires like bike tires. It's incredibly simple and straightforward.

LesterOfPuppets

Sure, it CAN press down on the top of the valve but you really don't want it to.

dscheidt

It depends on the pump head. Quite a lot of combination shraeder and presta valve heads do press the pin.

None of my tubes currently on my bikes (none of which were made in Taiwan) have the problem of sticking.

Turtle Speed

Whoah whoah whoah... a Presta valve isn't supposed to be hissing and losing air as the pump hose is removed from it? ...As long as the pump head isn't stuck in so deeply that the valve head is being depressed while the head is engaged?

I never knew that. I thought it was all just about the weight/slimness of it, or something.

I'm gonna start trying to see if I can inflate mine without putting the pump head in so deeply!

LesterOfPuppets

With a fresh Silca rubber you just need to get it past the cap threads, in that smooth ring before the nut threads start. Works for some other pump heads also.

fietsbob

schrader, pump heads, depress the spring check valve core center-pin,
presta has no spring, user touches their pin after un screwing the nut on it.
to break the air pressure closed seal. Then you add pressure.


more likely you are just venting the hose., pump, check valve and inner-tube stem valve
are closed on either end of the hose.

Vince Canepa

The Joe Blow Pro has Topeak's Smarthead, a dual Presta/Schrader chuck. It has to have a pin to depress the valve when used on Schrader valves, therefore I would argue that it is designed to work that way. In fact, if you look inside the Smarthead while you operate the locking lever, you can see the pin move slightly towards the "front", i.e. towards the valve.

If you don't want to lose air into the hose (air escapes through the open Presta valve and pressurizes the hose up to the pump's check valve) then you don't insert the Smarthead as far onto the valve. However, some Presta valves are "necked" down a bit at the end making this tricky, and sometimes the chuck will come off the valve when trying to pump the tire. The Presta valves that Shimano supplied with my Dura-Ace 7850 tubeless wheels are this way.

If the idea of the Presta valve is to prevent any air loss when you insert the valve (more important with an "onboard" pump than a floor pump) then tapping the valve stem before inserting the chuck defeats that purpose, doesn't it?

So back to the OP's original question, perhaps his Smarthead is worn. Or he can ignore it, unless of course it doesn't work when he tries to pump a tire with a Schrader valve.

HillRider

The idea isn't to prevent any air loss when you insert the valve in the pump head since you are going to add additional pressure anyway. Tapping the valve stem breaks the seal so air can enter the tube at a reasonable pressure differential and you will make up that small loss with the pump. The real intent is to prevent air loss when you remove the pump head.

ksisler

Wow... I had always kinda assumed that most folks would simple give the tip of presta valve a little tap with a finger to break loose any stuck ones before putting on the pump head. Am I missing something?

LesterOfPuppets

I remember having to learn that back when I first encountered presta valves. I don't think we're born with the instinct

From the OPs recounting of events it would seem there's a chance he didn't tap the valve after unscrewing it. This would explain why pumping didn't work 'til he had let the air out of the tube.

Digital_Cowboy

I have a slightly different problem with my Joe Blow Sprint. That is that I have somehow managed to lose the collar from the Schrader side of the chuck. It'd be nice to replace just that and not the entire chuck.

Vince Canepa

Being an old guy I well remember the days in the past when it was not necessary to tap the stem on a Presta valve. We simply slipped the chuck of our Silca frame (or floor) pumps onto the smooth valve body, pumped the tire and knocked the pump off with a whack of the palm. The valves opened without having to apply excess pressure. And the smooth valve bodies didn't tear up the rubber seal ring on the chuck or exert excess force on the valve body/tube joint. Also, because no air was lost putting the chuck on the valve, it meant less strokes of those frame pumps to top up the pressure which, for hard core tubular guys like me (I rode nothing but for 35 years) was every ride.

But the reality today is that many Presta valves stick closed. The Shimano valves I mentioned earlier can take as much as 160-170 PSI to open and sometimes, even that won't do it. Therefore you are either obliged to tap the valve stem or have the chuck do it for you, as the Smarthead does. It's just a convenience. Also, the threaded valve bodies common these days make a chuck with a locking device desirable. Until recently I used my old Silca floor pump but the Silca chuck seals don't last very long sliding on and off those threads. I had to resort to unscrewing the chuck from the end of the hose (the Silca dual Presta/Schrader chucks permit this), "screw" the chuck on the valve body, thread the hose onto the chuck, pump up the tire, then reverse the process. Kind of a PITA. After using a borrowed Joe Blow with the Smarthead I liked the convenience.

HillRider

Hey, the first time I tried to use a Presta valve, I couldn't get the tire to inflate at all until some kind soul informed me you had to unthread that little nut at the end of the stem!