Bicycle Mechanics - Educate me on the presta valve

It appears that there is a nut on the valve pin which needs to be loosened before air can be added or released. I am wondering if it is necessary to depress the valve pin before air can be added to the tube. With the nut on the valve pin loosened, will the pump push air into the tube with out having to depress the valve pin.

I am trying to come up with a system so that I can be confident that the air pressure in the tube is the pressure that was indicated on the pump after the inflator is disconnected. It seems that some air escapes when the inflator is disconnected.

So if someone can explain exactly how these air valves work, then maybe I can put my mind at ease.

Watch this video:

http://www.youtube.com/watch?v=9Ux08bz43qY

Don't worry about the sound of a tiny bit of air escaping when the pump head is removed. Normally its an insignificant amount of air.

Yes, loosen the little nut. I usually depress the valve pin once before pumping because it often gets stuck so that air can't get in. Once it's loose, you should be able to pump easily. If you forget to depress it first, and it is stuck, you will usually see the psi read very high immediately because the air in the pump hose has no where to go. That should indicate it's stuck and needs to be tapped with your fingertip.

Yes, loosen the little nut. I usually depress the valve pin once before pumping because it often gets stuck so that air can't get it. Once it's loose, you should be able to pump easily. If you forget to depress it first, and it is stuck, you will usually see the psi read very high immediately because the air in the pump hose has no where to go. That should indicate it's stuck and needs to be tapped with your fingertip.

+1 on all the points. It didn't used to be so, but modern PVs need to be burped once to unstick them. Once that's done the valve will act as a simple one way (check) valve and the pressure in the tube will always be equal to the hose pressure, until you reduce the hose pressure when disconnection.

With a typical pump, you'll see a spike in pressure with every stroke, which then settles as the air flows into the tire. It's that lower (settled) pressure that is equal to the tire pressure.

Presta valves work best if they are positioned near the 12-O-clock position on the wheel, which helps the un-sprung valve core more redily fall into the closed position. This way, all the air that you hear escaping when you detach the hose will be from the hose, not from the tire.

Having the pump head fitted straight-in-line on the Presta valve is critical to allowing the valve's core to open and shut freely. You may have to twist the hose at one of it's ends to allow the head to sit more straightly on the valve stem.

If the pump goes over your pressure target before the valve pops open, be careful as to how high the guage reads, since very-high, maximal gage readings tend to destroy the guage's calibration, causing it to forever read "high".
Also, with the pump and hose moderately over-pressurized, and with the Presta valve still stuck shut, you can rock the pump head sideways, which usually assists the valve popping open and immediately shows your actual tire pressure on the pump's guage without feeding in more than one or two psi to the tire's pressure. This will allow you to precisely monitor your tire's actual rate of pressure decline over one or more day's time.

Lastly, all Presta pump heads are intended to only engage the smaller-diameter threaded end of the Presta stem. Forcing the pump head gasket-packing over the major diameter of the stem will result in the pump head's gasket becoming leaky and permanently distended as well as requiring much more force to pull free of the valve, which can tear the valve away from the inner tube.
I will thus happily loan my expensive floor pump to kids with Shraeder valves on their wheels, but always hesitate to loan out my pump to experienced cyclists with Presta valves, as so few seem to know the proper way to fit the pump head!

Thanks for the explanations. I now feel better about the final pressure in my tube. I am going to see if I can attach my inflator such that no air escapes. With my current setup I always lose some air when I attach the inflator. This lets me know that I am also losing some air while I detach the inflator.

Since the presta valve is a one way valve or check valve unless you depress the pin, I can't see any reason to have my inflator depress the pin. A single burp of the pin as described should make sure that the valve is not stuck.

Thanks again.

Thanks for the explanations. I now feel better about the final pressure in my tube. I am going to see if I can attach my inflator such that no air escapes. With my current setup I always lose some air when I attach the inflator. This lets me know that I am also losing some air while I detach the inflator.

Since the presta valve is a one way valve or check valve unless you depress the pin, I can't see any reason to have my inflator depress the pin. A single burp of the pin as described should make sure that the valve is not stuck.

Thanks again.

Yes, chucks with valve pins on PV can be a nuisance. Try to fiddle with how far you fit the head, so the valve doesn't depress when you engage the thumb lock. This is why many old timers prefer the simple push-on chuck with a gasket shaped like a volcano.

As the pressure in the head increases it presses the sides of the cone gripping harder, making a simple, reliable seal. The drawback is that it's very easy to break the nut off with this type of head, so the better ones have some kind of pressure release button, to bleed out the hose before you yank off the head.

BTW- valve orientation while pumping doesn't matter because the force from pressure behind the valve dwarfs the effects of gravity on the 2 gram (if that) moving part.

In my experience pressure guages built into the pump give inaccurate and inconsistent pressure readings. A hand held guage will give far more useful readings.

Thanks for starting a topic on such a simple question Jim. I'm mostly new to presta too and learned a couple of things. Maybe I'll start taking presta valve classes. Man, this is a lot more intricate than Schrader.

I prefer Schraders because they will take more abuse. However, Prestas, handled carefully, will give you good service. bk

In my experience pressure guages built into the pump give inaccurate and inconsistent pressure readings. A hand held guage will give far more useful readings.

It's possible to calibrate even the inexpensive guages on most floor pumps, if you have a reference-standard guage to compare to.

I've rotated the needle, wound it quite a ways, to effect a permanent change in the 0-psi rest position (clear of the stop post for comparitive readings.
In certain cases, I moved the needle until the gear drive actually skipped a tooth, then advanced to an exact position in the other direction.
You can also get the needle to move on the drive post in some cases, but either way can give extremely accurate readings within a useful pressure range that's used for your tires.

It's still handy to have the hand-held guage around, to simply check the pressure, but my floor pump is handy too and it gets the pressure-check done in no time while I top up any pressure losses.

BTW- valve orientation while pumping doesn't matter because the force from pressure behind the valve dwarfs the effects of gravity on the 2 gram (if that) moving part.

It might be stated more precisely to say that *air movement* through the valve dwarfs the effects of gravity on the ~2 gram part.

True in most cases, but not always true. If the leakage rate of the presta head seal is moderate (i.e. average, somewhat normal), there is pressure loss the moment that pumping effort ceases, and until the pumphead is perhaps sharply pulled off the valve stem, this lost air's effect on pressure is cumulative and unknown.
With the valve inverted at 12-O-clock, the air flow (however slight) can become strictly one-way, as long as the chuck isn't so sideways as to hold the valve open.

Riders in the old days knew that the valving action when using valve-less frame pumps worked better with the valve up top of the wheel, the better to reduce the incidence of a blown-back pump handle, but it was perhaps even more important to hold the pump's head squarely with the axis of the valve stem.

Thanks for the explanations. I now feel better about the final pressure in my tube. I am going to see if I can attach my inflator such that no air escapes. With my current setup I always lose some air when I attach the inflator. This lets me know that I am also losing some air while I detach the inflator.

Some inflator heads are easier to use than others.

If you use a floor pump, you can use an after market head like these ones:

http://www.bikepartsplace.com/discount/pump-end-40/

http://www.flickr.com/photos/28270886@N02/2650182576/

I keep a Presta valve adapter on my tubes in place of a cap and fill them with a Schrader pump and check them with a Schrader gage. I find it only takes a second to take adapter off turn it around and open the Presta nut and fill and check. Remove it tighten nut flip it around and replace it as a cap.

http://compare.ebay.com/like/200784507731?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

I keep a Presta valve adapter on my tubes in place of a cap and fill them with a Schrader pump and check them with a Schrader gage. I find it only takes a second to take adapter off turn it around and open the Presta nut and fill and check. Remove it tighten nut flip it around and replace it as a cap.

http://compare.ebay.com/like/200784507731?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

I used to use these with a Shraeder head in the old days, and found that with the right lenght of adapter, that the Shraeded head valve-depressing plunger would effectively open (and allow to close) the valve as the lever-lock was applied.
This also worked extremely well with the good Shraeder guage that I had, but again, the adapter's length was critical.

I prefer Schraders because they will take more abuse.

I can't see any advantage whatsoever in the Prestas. Greatest scam perpetrated on the American public since 1 hour Martinizing.

It appears that there is a nut on the valve pin which needs to be loosened before air can be added or released. I am wondering if it is necessary to depress the valve pin before air can be added to the tube. With the nut on the valve pin loosened, will the pump push air into the tube with out having to depress the valve pin.

What exactly do you mean by "depress"?

It is a good idea to tap the Presta valve a few times with your finger before attaching the pump hose - it helps the valve to get "unstuck".

But if you are asking whether the pump head is supposed to keep the valve tip pressed down when attached, the the answer is no. A typical Presta pump head does not depress Presta valves when attached and is not supposed to do so. The valve is opened by the incoming air pressure and only by the incoming air pressure. After the first pump that opens the valve, the pressure in the pump hose will equalize with the pressure inside the tube, meaning that the Presta valve, once opened, will no longer close (until you detach the pump head that is).


I am trying to come up with a system so that I can be confident that the air pressure in the tube is the pressure that was indicated on the pump after the inflator is disconnected.

Huh? Disconnected? After the inflator (pump head?) is disconnected the pump pressure will show exactly zero. What are you talking about?


It seems that some air escapes when the inflator is disconnected.

When you disconnect the standard pump head from the valve, the Presta valve closes instantly. The air does not escape from the tube when you detach the head (only a very very very tiny amount escapes). The short burst of escaping air that you hear when you detach the pump is the residual pressure from the pump hose. I.e. it is the air from the pump, not the air from the tube that makes that sound.


So if someone can explain exactly how these air valves work, then maybe I can put my mind at ease.

Your pump has a built-in one-way internal valve. It is typically located at the base of the pump (for floor pumps). This built-in valve is what is responsible for keeping the air in the tube when the pump head is attached. The Presta valve in your tube does not really "work" when you are pumping up the tube: since the pressure in the pump hose and inside the tube is identical, the Presta valve simply stays permanently open. However, when you begin detaching the pump head from Presta valve, the seal gets broken, the pressure in the pump hose quickly drops and the Presta valve instantly closes, sealing off the tube.

There are "alternative" pump head designs out there that contain a pin, which is intended to mechanically open the Presta valve when you attach the head to the valve. Such designs work better with "sticky" valves, but at the same time they lose more air when detached.

Andrey, thanks for the additional information. I think that I now know exactly what I need to make sure that I am airing up my tires correctly.

The pressure differential , higher in the tube than the outside air closes the check valve.
the little nut is a positive closure back -up.

floor pumps also have a check valve , so the hose holds pressure..

venting the hose, does not let air out of the tire.

Schrader valves, each has a spring, so the pump-head has to open the valve
by pressing in the center pin.

I can't see any advantage whatsoever in the Prestas. Greatest scam perpetrated on the American public since 1 hour Martinizing.

Ah, those French. Developing a simple lightweight technology that takes a little finesse, when they know Americans are klutzy brutes. ;)

The Presta valve is better when the rim is very narrow. The thicker Shraeder stem requires a bigger hole in the rim, and the thick rubber pad at the base of a typical Shraeder tube's valve stem is barely accomodated between the tire's beads.

Presta valves more easily separate from the tube, but Shraeder valves sometimes get a pressurized blister in the rubber coating, leading to rapid air loss.

A pocket-type air pump can have a lighter attachment head with Presta, no need for a valve-depressing plunger or the bulk to accomodate any moving parts.
The Presta valve stem appears to be lighter and more aerodynamic.

Shraeder valves require a cap to keep dirt from settling in the stem, which gets blown into the pump head as soon as the leverlock is actuated. This can foul the mechanism on some pump heads.

For racing bikes, Presta gets the nod. But for most others, Shraeder is easier overall.
Presta is the standard for road bikes, and certain pocket pumps are dedicated Presta-only.

Lastly, very narrow Shraeder tubes end up with the thick pad wrapping at least half-way around the tube, which confines all of the tube's elastic expansion to the strip of thin rubber opposite the thicker rubber pad. This can more readily lead to rupture if the tube is used in a larger tire.

I believe that Presta valves (more specifically their attachment to the tube) would prove more durable if users only knew that their Presta pump head is only supposed to by fitted to the narrow tip of the valve stem. This would greatly reduce the forces that typically lead to failure.

I believe that Presta valves (more specifically their attachment to the tube) would prove more durable if users only knew that their Presta pump head is only supposed to by fitted to the narrow tip of the valve stem. This would greatly reduce the forces that typically lead to failure.

None of the pumps I've ever owned have fit to that area. It's always been on the thicker part of the stem, and I've never had a problem with presta durability. You must have a different type of pump head than Park, Topeak, etc.

Thanks for all the information. I can now air up my tires like a professional.

My current set up is a compressor that I can set the pressure on. I have a schrader inflator with a trigger at the end of the compressor hose. I use a presta to schrader adapter on the tube. In the past I would screw the adapter all the way down on the presta stem. This caused air to escape when I attached the inflator. Now I only screw the adapter onto the presta stem about 3 turns and when I attach the inflator no air escapes. I can trigger the inflator and the air enters the tube and when I release the trigger only the air trapped in the inflator escapes. Seems to be a perfect operation to me.

Thanks again.

No that this hasn't already been answered, but this is a good guide too;

http://www.madegood.org/bikes/library/inflate-a-tyre-with-a-presta-or-sports-valve/

But if you are asking whether the pump head is supposed to keep the valve tip pressed down when attached, the the answer is no. A typical Presta pump head does not depress Presta valves when attached and is not supposed to do so.

It works well though; I've tried filing an adapter down to mimic a Shrader, and it gives a better pressure reading. Pumping a Presta in the usual way, you're only reading the pressure in the hose, because the valve is normally shut except in the lower part of your downstroke. If you pay attention, you can hear and actually feel it opening and closing through the pump.

Although if you're going to calibrate your gauge, there's no point, since it should be a consistent bias.

At least it's only Shrader and Presta nowadays.

I recently bought a 2nd hand bike that still used Woods valves. What a nightmare to inflate those.
It's the first time I binned a perfectly useable set of inner tires. It now wears Schraders.

None of the pumps I've ever owned have fit to that area. It's always been on the thicker part of the stem, and I've never had a problem with presta durability. You must have a different type of pump head than Park, Topeak, etc.

The newer "universal one-hole" Presta/Shraeder pump heads have a collapsible elastic grommet that can squeeze down on anything from a Shreader to the thick part of a Presta valve, but single-purpose valve ports on pump heads (even on "twin-heads") that are for Presta valves all are supposed to only grip the small end of a Presta valve, but over time can get hogged-out to where they must be fitted to the larger part of a Presta valve. Even the old Silca heads with the monster-grommet inside would seal fine on the reduced end of a Presta valve when new, but admittedly many of those eventually became more loose-fitting from mis-use.

The design intent of having the grommet grip the smaller portion of the Presta valve stem was to allow higher sealing pressure while requiring a low amount of force to pull the head free of the valve.
The newer pumps with collapsing grommets aren't intended to be pulled forcefully off of the valve (lever is supposed to be unlocked first), so having the grommet grip the thicker part of the valve stem is not an issue.

I never use the plastic valve cover that comes with the tubes. It will keep the end of the valve from cutting the tube when it's rolled up, but isn't necessary on the bike.

I prefer tubes with smooth stems, instead of threaded. It's easier to remove the pump head without having to pull too hard on it. And smooth stems don't have a nut to tighten down against the rim.

One issue with smooth stems is that you can't tighten a nut to stop rattling, mostly in deeper rims.
But a nut seems like a really poor way to cure the rattling, so some shrink-wrap or even a twist of electrical tape is good enough.

I don't use the nuts or caps on Presta valves myself, except for rolling up an airless tube (as you said).

Again though, for pumps that have to be pulled off of a Presta valve, those are designed to grip only the reduced, threaded end of the valve stem, so I'm guessing that your pumphead grommet is toast.

Pumping a Presta in the usual way, you're only reading the pressure in the hose, because the valve is normally shut except in the lower part of your downstroke.

I don't see why it would be true. Presta valve has no springs inside. The only force that keep Presta valve closed is the pressure differential between the tube and the "outside world".

Once you started pumping and the Presta valve opens for the first time, the pressure between the tube and the pump hose equalizes. This means that Presta valve does not close anymore (as long as the seal around the pump head is sufficiently airtight). As long as the outside pressure is the same as inside pressure there's simply no force that would close it. Once the pressure is equalized, the only force that can move the valve core is the weight of the core itself. If you pump you tires in 6 o'clock position, the weight of the core should actually keep it open, not closed.


If you pay attention, you can hear and actually feel it opening and closing through the pump.

I can only hear it open on the first stroke of the pump. It makes a distinctive "click". Any further strokes extract no sounds from the Presta valve. If I release some pressure from the pump hose by turning a release screw at the base of my pump, the Presta valve will indeed close. And the next pump stroke will make it open with a "click" sound again.

If in your case Presta valve opens and closes at each stroke of the pump, it probably means that there's an air leak on the pump side of the valve. The pressure in the hose bleeds off rather quickly, making the Presta valve close after each stroke. In my case it simply doesn't happen.

...If in your case Presta valve opens and closes at each stroke of the pump, it probably means that there's an air leak on the pump side of the valve. The pressure in the hose bleeds off rather quickly, making the Presta valve close after each stroke. In my case it simply doesn't happen.

Many pumps seem lose a small volume of the pressurized air in the hose simply to the pump's valve closing, which then allows a Presta valve to slightly "stick" shut each time the pump handle is pulled back, so it may not actually take a "leak" to cause the audible valve sticking.

Also, many hand-held pumps have no valve at all, relying entirely on the Presta core itself to keep the air moving in only one direction.
This is why one must hold such pump's heads squarely with the valve, lest the Presta core get cocked open, thus allowing the tire's pressure to blow the handle back forcefully toward the operator's "vitals".

If in your case Presta valve opens and closes at each stroke of the pump, it probably means that there's an air leak on the pump side of the valve. The pressure in the hose bleeds off rather quickly, making the Presta valve close after each stroke. In my case it simply doesn't happen.
My steel and cast-iron Zefal Husky has no leak; the pressure reading stays constant. I'd say it's simply the hose stretching enough to allow some backflow after the pressure pulse that opens the valve. Or perhaps it just takes more backflow to actuate the pump's valve than the presta.

I'm fairly sure, but not certain, every other floor pump I've used has been the same... I'll take note of the score next time I use another pump.

At least it's only Shrader and Presta nowadays.

I recently bought a 2nd hand bike that still used Woods valves. What a nightmare to inflate those.
It's the first time I binned a perfectly useable set of inner tires. It now wears Schraders.
The beauty of the Woods valve is that a Schraeder valve is a direct replacement. Same outer diameter. I've dealt with enough Woods valves to know what you're talking about. They can be a major PITA.

On the subject of valve sticking, some Presta valves stick shut tightly, and some do not.

I have such a pair of Presta valves on my main go-fast bike, and the rear tube's Presta valve is fiercely sticky, to the extent that I MUST rock the pump head back and forth to help it open, even with 180psi trying to go in. The front tube's valve "pops" open on it's own with only modest over-pressure after sitting overnight with 80psi behind it.

I've noticed a little variation from presta to presta, but nothing like that.

Hi, thought I'd post my question on a presta valve issue here on this older thread to minimize forum noise...

I've been using presta valve tubes for a long while now, but recently I've run into a rash of broken presta pins, e.g., yesterday on a group ride. Luckily a fellow rider offered me a new tube so I could get back to town to get a couple new replacements. As he was helping me change my flat (again) I noticed that his technique was to open the stem all the way out, and turn it back ~1/2 of its threads and proceed to engage the pump.
I'm wondering if my breaking presta pins is the result of me loosening the valve too much, or, as my initial belief, I'm buying poorly manufactured tubes.
I've never heard an official statement of presta use mentioning this, only a smattering of folks who believed this could be the problem.

I've been using presta valve tubes for a long while now, but recently I've run into a rash of broken presta pins, e.g., yesterday on a group ride. Luckily a fellow rider offered me a new tube so I could get back to town to get a couple new replacements. .

First of all a broken pin is meaningless to the function of the valve which will work fine, except that you can no longer use a pressure gauge. That's true unless they're making valves materially worse today than in the past.

As to why you're breaking pins, it's probably related to your pumping skills, especially if using a hand pump. Many people rock or otherwise work the pump against the valve while pumping which initially bends the pin, then later snaps it off.

When using a hand pump brace the thumb of the valve end hand against the tire to stabilize the pump. Also, don't overly brace he bike, and instead let it rock somewhat with your hand motion. When finished, don't work a tight head off, instead release the thumblock (if any) and remove the pump with a swift karate chop or punch. This pushes it straight off withour stressing the pin.

If using a floor pump with a push-on head which clinches with air pressure, find a way to bleed the hose before pulling the head off. Sometimes you can bleed by rocking the head to one side or pulling it back slightly. Or you can do as I've done for 45 years, and adapt the head with a bleeder valve (presta valve drilled and glued into the side or top), allowing you to bleed the head easily before yanking it off.

I think I heard somewhere how Presta valves were "invented". I believe they were using Schrader valves on some vehicle that was setting a land speed record (like a drag racer or something). They found that the front tires were deflating during the fast runs. The centrifugal force was forcing the little valve thingy inside the Schrader valve to move towards the outside, letting the air out!

I think I heard somewhere how Presta valves were "invented". I believe they were using Schrader valves on some vehicle that was setting a land speed record (like a drag racer or something). They found that the front tires were deflating during the fast runs. The centrifugal force was forcing the little valve thingy inside the Schrader valve to move towards the outside, letting the air out!

I think this is just an urban legend. PVs are older than serious land speed records, having been used on bikes in Italy and France for well over half a century. In any case the easy solution to SV bleed at speed (which I doubt is true) would be to put a metal valve cap over the valve.