Sticking Presta valves

Joe Riel said:

Whenever pumping air into a tire, I briefly depress the valve stem
(Presta) to prevent it from sticking. Despite this precaution, I
notice that the valves stick quite frequently. That is, they won't
accept air until the pressure in the pump exceeds that in the tire
by a considerable amount, maybe 40psi. Given that I am, ummm,
mass-challenged, this often requires having to remove the pump head
and release more pressure. Once air enters, the valve does not
stick again, at least not until the next time I have to pump them.

Quoted message said:

Any good explanation for this? Why doesn't the initial depression
prevent sticking? One possibility is that the top of the valve stem
hits the inside wall of the pump head and causes it to jam. I
haven't tested for that but consider it unlikely.

That would only release air from the tire and that is how most Silca
plastic frame pumps were destroyed, as the piston was ejected from the
pump body, stripping (splitting) the pump housing.

The Presta valve has no spring to seat the seal and since either that
or a different seal is required to assure reliable closure, the Presta
valve seat is conical. A cone is essentially a wedge and seats with
more friction than a face contact as the Schrader valve has.

I would rather hand pump Presta than Schrader valves considering how
much more air pressure spring loaded Schrader valves require to open
than most Presta valves. I find that once I begin pumping, the
release force (pressure) is insignificant compared to the force
required to reach 100psi or so. In any case, I suspect that is what
the ancients thought when they came up with the Presta valve.

I don't know the history of this valve but was surprised to discover
that the three threads they have are all English pitch. The valve
core body thread is so truncated that it is probably about 1/3 the
depth of a full thread.

http://www.geocities.com/cyqlist/valve.html
http://www.geocities.com/cyqlist/pcore.jpg

Jobst Brandt
[email hidden]

<[email hidden] wrote: (clip) I would rather hand pump
Presta than Schrader valves considering how much more air pressure spring
loaded Schrader valves require to open than most Presta valves. (clip)
^^^^^^^^^^^^^
All the Schrader valve couplings I have used have a little "[censored]" that is
supposed to open the valve. If I find pumping is unduly hard, I release the
clamp and reseat the coupling. This generally helps a lot.

Quoted message said:

http://www.geocities.com/cyqlist/valve.html
http://www.geocities.com/cyqlist/pcore.jpg

In the picture of the removable Presta core, there is dark region
around the circumference of the inner end of the brass "piston" (the
moveable valve). Is that a thin rubber(ish) seal? If so, presumably
that is what causes (with the taper) the high friction.

Joe

On Tue, 30 Nov 2004 03:13:29 GMT, [email hidden]

Quoted message said:

I would rather hand pump Presta than Schrader valves considering how
much more air pressure spring loaded Schrader valves require to open
than most Presta valves.

Schrader-valve pumps have a check valve in the outlet of the pump
cylinder and a valve depressor in the coupling. For that matter,
Presta-valve pumps ordinarily have that check valve as well. You knew
that already, right?

By the way, a low-tension version of the Schrader exists which opens
at pressure differentials as low as 2 psi. It's used in automotive
compression testers. I like to keep a few around, but they're damned
hard to come by; on the last occasion that I ordered some from
Snap-On, they shipped the ordinary high-break type, which is useless
for compression tester applications. (Mac Tools has always been a
far more reliable source for these valves, but sometimes they ship one
with a long tail on it that won't work in a tire valve stem...or my
favorite compression tester.)

Quoted message said:

I find that once I begin pumping, the
release force (pressure) is insignificant compared to the force
required to reach 100psi or so. In any case, I suspect that is what
the ancients thought when they came up with the Presta valve.

Whatever they had in mind, a better job could be done with it today,
but the last thing we need is a *fourth* standard for tire valves.

Quoted message said:

I don't know the history of this valve but was surprised to discover
that the three threads they have are all English pitch. The valve
core body thread is so truncated that it is probably about 1/3 the
depth of a full thread.

Schrader, right? No, they're more like 75% on the ones I've got,
which is realtively typical.

Quoted message said:

http://www.geocities.com/cyqlist/valve.html
http://www.geocities.com/cyqlist/pcore.jpg

The most maddening thing about dealing with Schrader valves (when
they're used in non-tire applications like the ports of an air shock)
is that while the threads are dimensioned in English units, the bloody
things are a [censored] size which is next to impossible to finds in taps
and dies. Rigging up pressure lines for unusual purposes can be a
right royal pain in the neck as a result; the only reliable source
I've found for couplers is in the hardware kits for air shocks, and
those are, in polite terms, not terribly robust.
--
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Joe Riel writes:

http://www.geocities.com/cyqlist/valve.html
http://www.geocities.com/cyqlist/pcore.jpg

Quoted message said:

In the picture of the removable Presta core, there is dark region
around the circumference of the inner end of the brass "piston" (the
movable valve). Is that a thin rubber(ish) seal? If so,
presumably that is what causes (with the taper) the high friction.

The black seal at the end of the plunger is normally a rectangular
cross section rubber ring. It gets pressed into a tapered bore to
give a reliable seal even without screwing down the lock nut.
However, at high speeds, centrifugal force can cause an unsecured
valve to leak. This has been tested on a fast descent at over 50mph
by Tom Ritchey in the days when he routinely did not secure the lock
nut. You can imagine how much "I told you so" he got from other
riders on that Sierra tour.

Jobst Brandt
[email hidden]

"Joe Riel" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Whenever pumping air into a tire, I briefly depress the valve stem
(Presta) to prevent it from sticking. Despite this precaution, I
notice that the valves stick quite frequently. That is, they won't
accept air until the pressure in the pump exceeds that in the tire by
a considerable amount, maybe 40psi. Given that I am, ummm,
mass-challenged, this often requires having to remove the pump head
and release more pressure. Once air enters, the valve does not stick
again, at least not until the next time I have to pump them.

Any good explanation for this? Why doesn't the initial depression
prevent sticking? One possibility is that the top of the valve stem
hits the inside wall of the pump head and causes it to jam. I haven't
tested for that but consider it unlikely.

Joe

Try a differnt pump.

Marty

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Joe Riel said:

Whenever pumping air into a tire, I briefly depress the valve stem
(Presta) to prevent it from sticking. Despite this precaution, I
notice that the valves stick quite frequently. That is, they won't
accept air until the pressure in the pump exceeds that in the tire
by a considerable amount, maybe 40psi. Given that I am, ummm,
mass-challenged, this often requires having to remove the pump head
and release more pressure. Once air enters, the valve does not
stick again, at least not until the next time I have to pump them.

Quoted message said:

Any good explanation for this? Why doesn't the initial depression
prevent sticking? One possibility is that the top of the valve stem
hits the inside wall of the pump head and causes it to jam. I
haven't tested for that but consider it unlikely.

That would only release air from the tire and that is how most Silca
plastic frame pumps were destroyed, as the piston was ejected from the
pump body, stripping (splitting) the pump housing.

The Presta valve has no spring to seat the seal and since either that
or a different seal is required to assure reliable closure, the Presta
valve seat is conical. A cone is essentially a wedge and seats with
more friction than a face contact as the Schrader valve has.

I would rather hand pump Presta than Schrader valves considering how
much more air pressure spring loaded Schrader valves require to open
than most Presta valves. I find that once I begin pumping, the
release force (pressure) is insignificant compared to the force
required to reach 100psi or so. In any case, I suspect that is what
the ancients thought when they came up with the Presta valve.

I don't know the history of this valve but was surprised to discover
that the three threads they have are all English pitch. The valve
core body thread is so truncated that it is probably about 1/3 the
depth of a full thread.

http://www.geocities.com/cyqlist/valve.html
http://www.geocities.com/cyqlist/pcore.jpg

Jobst Brandt
[email hidden]

The standard Schader valve is 1/16 " BSP.
British Standard Pipe.

Marty

Joe Riel said:

Any good explanation for this? Why doesn't the initial depression
prevent sticking? One possibility is that the top of the valve stem
hits the inside wall of the pump head and causes it to jam. I haven't
tested for that but consider it unlikely.

I don't know why the presta valve sticks. What I do know is that if
you use a Topeak Smarthead with your pump, when you lift the lever to
lock the head onto the valve, it will depress the top of the silica
valve head. It makes the presta valve work somewhat like a Schrader.

Quoted message said:

Joe Riel said:

Whenever pumping air into a tire, I briefly depress the valve stem
(Presta) to prevent it from sticking. Despite this precaution, I
notice that the valves stick quite frequently. That is, they won't
accept air until the pressure in the pump exceeds that in the tire
by a considerable amount, maybe 40psi.

Quoted message said:

I would rather hand pump Presta than Schrader valves considering how
much more air pressure spring loaded Schrader valves require to open
than most Presta valves. I find that once I begin pumping, the
release force (pressure) is insignificant compared to the force
required to reach 100psi or so. In any case, I suspect that is what
the ancients thought when they came up with the Presta valve.

I'm with Joe on this one. If my tires are at 80 psi and I want to top
them off to 100 psi, I have to get the pump up to 120 psi in order to
get started. Maybe I don't have the greatest pump in the world, but that
extra 20 psi makes a big difference in the force required. The sticky
valve issue is one that has annoyed me since I started riding a road
bike with presta valves in the early '90s, and I'd be interested in a
reasonable solution to the problem.

My current solution is to use a compressor with a schraeder valve chuck
and a presta -> schraeder valve adapter on the tire. When you hook that
up, the presta valve is depressed by the tab in the chuck and the sticky
valve problem is avoided.

The downsides are that the compressor was expensive (~70 USD if memory
serves), the adapter needs to be moved around (unless you get enough
adapters for all of your wheels), and the low-end compressor is probably
not capable of delivering 120 psi or more to the skinny tires on my
racing bike.

--
Dave
dvt at psu dot edu

Joe Riel said:

Whenever pumping air into a tire, I briefly depress the valve stem
(Presta) to prevent it from sticking. Despite this precaution, I
notice that the valves stick quite frequently. That is, they won't
accept air until the pressure in the pump exceeds that in the tire by
a considerable amount, maybe 40psi. Given that I am, ummm,
mass-challenged, this often requires having to remove the pump head
and release more pressure. Once air enters, the valve does not stick
again, at least not until the next time I have to pump them.

Any good explanation for this? Why doesn't the initial depression
prevent sticking? One possibility is that the top of the valve stem
hits the inside wall of the pump head and causes it to jam. I haven't
tested for that but consider it unlikely.

Joe

try a different brand of tube. i have a cheapo perfomance brand tube
that behaves exactly as you describe. my michelins & torelli's don't.

dvt said:

I'm with Joe on this one. If my tires are at 80 psi and I want to top
them off to 100 psi, I have to get the pump up to 120 psi in order to
get started. Maybe I don't have the greatest pump in the world, but that
extra 20 psi makes a big difference in the force required. The sticky
valve issue is one that has annoyed me since I started riding a road
bike with presta valves in the early '90s, and I'd be interested in a
reasonable solution to the problem.

Do you give the valve stem a little tap before pumping? I do. Only a tiny
amount of air escapes, and I can easily top off a tire with a couple of
strokes. I'm using a Silca floor pump.

Art Harris

Joe Riel said:

Whenever pumping air into a tire, I briefly depress the valve stem
(Presta) to prevent it from sticking. Despite this precaution, I
notice that the valves stick quite frequently. That is, they won't
accept air until the pressure in the pump exceeds that in the tire by
a considerable amount, maybe 40psi. Given that I am, ummm,
mass-challenged, this often requires having to remove the pump head
and release more pressure. Once air enters, the valve does not stick
again, at least not until the next time I have to pump them.

Any good explanation for this? Why doesn't the initial depression
prevent sticking? One possibility is that the top of the valve stem
hits the inside wall of the pump head and causes it to jam. I haven't
tested for that but consider it unlikely.

It's been my experience that this characteristic varies by
manufacturer. Michelin Ultra Lights (didn't these used to be called
Air-Stops?) almost never stick, but Continental tubes are the worst
offenders. I recently bought a batch of Schwinn tubes from a friend
who closed his Schwinn store, and these sometimes stick also.

I've often pumped to the limit of the pressure gauge on my pump
(Performance Hurricane, 160 lbs/11 bar) without getting the valve to
release, but if I push the chuck onto the valve stem really far the
valve will be pushed open by the little green thingy at the base of
the rubber sleeve. You'll know it's open when the gauge registers
pressure.

jeverett3<AT>earthlink<DOT>net http://home.earthlink.net/~jeverett3

Harris said:

Do you give the valve stem a little tap before pumping? I do.

So do I.

Quoted message said:

Only a tiny
amount of air escapes, and I can easily top off a tire with a couple of
strokes. I'm using a Silca floor pump.

Your pump is probably better than mine; mine is about 10 years old and
has the name "Giant" in big white letters on the side. I don't know who
made it, but I doubt my pump is as nice as your Silca.

That is a bit beside the point, of course. If the valve design could be
modified slightly to get rid of this "overhead," the pump wouldn't have
to be designed for 150 psi in order to get 120 psi in the tire.

--
Dave
dvt at psu dot edu

jim beam said:

try a different brand of tube. i have a cheapo perfomance brand tube
that behaves exactly as you describe. my michelins & torelli's don't.

To study this a bit, I cut open a presta stem and measured the
diameter of the rubber wedge, it is approximately 0.12inch. With a
40psi differential (my estimate of the amount it takes to get it
started, when sticking), the force on the piston is 0.45 lb. That
seems quite high. On the valve I cut apart (which did not exhibit the
problem) I could detect no sticking after forcefully seating the
valve. I also could detect no sticking on a tube that does exhibit
the problem. That is, I let all the pressure out of the tube, pulled
up on the valve nut to seat the seal, then released it. It fell down,
that is, it took essentially no force to unseat it. So I'm currently
at a loss to explain this. I'll attempt to measure the opening force
when under pressure, however, my "lab equipment" is primitive.

Joe

Joe Riel said:

jim beam said:

try a different brand of tube. i have a cheapo perfomance brand tube
that behaves exactly as you describe. my michelins & torelli's don't.

To study this a bit, I cut open a presta stem and measured the
diameter of the rubber wedge, it is approximately 0.12inch. With a
40psi differential (my estimate of the amount it takes to get it
started, when sticking), the force on the piston is 0.45 lb. That
seems quite high. On the valve I cut apart (which did not exhibit the
problem) I could detect no sticking after forcefully seating the
valve. I also could detect no sticking on a tube that does exhibit
the problem. That is, I let all the pressure out of the tube, pulled
up on the valve nut to seat the seal, then released it. It fell down,
that is, it took essentially no force to unseat it. So I'm currently
at a loss to explain this. I'll attempt to measure the opening force
when under pressure, however, my "lab equipment" is primitive.

Joe

do the wedges have the same taper? if i pump up the sticky valve i have
and quickly remove the pump, i can see several threads of the valve
head creep forward over the course of about 20 seconds. after that
time, it's well and truly stuck in there. other brands don't do that.
i've not disassembled one of these valves, so i'd guess it's either the
taper or some particularly soft kind of rubber gasket that the wedges
seat in.

jim beam said:

do the wedges have the same taper?

I've only cut open the one. I have a few different brands of old,
unpatchable tubes lying around (never know when they might come in
handy) so will dissect them and record any differences in the valve
construction.

Quoted message said:

if i pump up the sticky valve i
have and quickly remove the pump, i can see several threads of the
valve head creep forward over the course of about 20 seconds. after
that time, it's well and truly stuck in there. other brands don't do
that.

Interesting. I'll try to duplicate that. A clear pump head would be
nice, but I'm not likely to come across one of those any time soon.

Quoted message said:

i've not disassembled one of these valves, so i'd guess it's
either the taper or some particularly soft kind of rubber gasket that
the wedges seat in.

I was thinking maybe the rubber is much thicker on those that stick.

Joe

Harris said:

dvt said:

I'm with Joe on this one. If my tires are at 80 psi and I want to top
them off to 100 psi, I have to get the pump up to 120 psi in order to
get started. Maybe I don't have the greatest pump in the world, but
that extra 20 psi makes a big difference in the force required. The
sticky valve issue is one that has annoyed me since I started riding
a road bike with presta valves in the early '90s, and I'd be
interested in a reasonable solution to the problem.

Do you give the valve stem a little tap before pumping? I do. Only a
tiny amount of air escapes, and I can easily top off a tire with a
couple of strokes. I'm using a Silca floor pump.

Yeah, no kidding. This kind of goes without saying, but I guess someone had to
say it. Always un-stick a Presta valve before attatching the pump. If I don't
do this, my pump will blow off the stem before any air goes in the tire.

Matt O.

dvt said:

I'm with Joe on this one. If my tires are at 80 psi and I want to top
them off to 100 psi, I have to get the pump up to 120 psi in order to
get started. Maybe I don't have the greatest pump in the world, but that
extra 20 psi makes a big difference in the force required. The sticky
valve issue is one that has annoyed me since I started riding a road
bike with presta valves in the early '90s, and I'd be interested in a
reasonable solution to the problem.

Sometimes, spritzing a little soapy water into the valve before
attaching the chuck will keep the valve from sticking after it first
unseats. Otherwise, I've found the same thing that you did; a
Schrader adapter and chuck will often depress the valve.

--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

On Tue, 30 Nov 2004 06:29:17 GMT, [email hidden]

Quoted message said:

Joe Riel writes:

http://www.geocities.com/cyqlist/valve.html
http://www.geocities.com/cyqlist/pcore.jpg

Quoted message said:

In the picture of the removable Presta core, there is dark region
around the circumference of the inner end of the brass "piston" (the
movable valve). Is that a thin rubber(ish) seal? If so,
presumably that is what causes (with the taper) the high friction.

The black seal at the end of the plunger is normally a rectangular
cross section rubber ring. It gets pressed into a tapered bore to
give a reliable seal even without screwing down the lock nut.

Well, some of the time, anyway. I may be buying crappy tubes (which,
at $5 each for the long-stem 700 tubes for the road bike, really
annoys me) but about one in five seems to leak if not firmly
tightened, even after it's been in service for a few days. Some only
leak until they've been run tight for a while; some will leak if not
tightened no matter what.

Quoted message said:

However, at high speeds, centrifugal force can cause an unsecured
valve to leak. This has been tested on a fast descent at over 50mph
by Tom Ritchey in the days when he routinely did not secure the lock
nut. You can imagine how much "I told you so" he got from other
riders on that Sierra tour.

Hmm. I have to wonder how much of that was centrifugal force and how
much was vibration causing the valve stem to shake and walk the seal
down the taper. If spinning smoothly, the revs required to overcome
the tire pressure should be *huge*. Of course, if that nut wasn't
needed, I rather suspect that it would not be staked in place...
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.