necrowinter

I dont know if my pump is acting up or if the tube has an issue.

Anyway, this is what I do:

1) take off the cap
2) unscrew the presta valve until its all the way off
3) Press on the valve to get air to come out
4) I put the pump onto the valve and attempt to put air in it

I get all sorts of weird things. My pump basically follows a pattern, it goes from 0, 80, 100, 120 and then falls back down to 80.

To me this implies its not on all the way but I cant put it on anymore. Im afraid if I press it down any harder I can mess up my tube.

I was able to do the front one but I cant get the back one. I have a floor pump that can do the schrader or presta.

When I did the front tire it never did anything weird but I didnt hear air come out when I put the pump on. I inflated these tires before but I just cant get this back tire to inflate, at least I dont know if it is or not my pump isnt giving me a good reading. The tire is currently holding air and is usable.

what is going on?

mctrek

I would take all the air out of the presta tube and then try to inflate it. Make sure that the pump is clamped and set for the Presta valve and not for the Schrader valve. It sounds like you are following the right steps and if the other presta tube is inflating then I would guess something is broken on your presta valve.

Wilfred Laurier

a few thoughts

i have used pumps with a two sided
presta and schraeder
head
and if there is insufficient back pressure on the side of the head you are using
air goes out the other side
if you do not have a pump with a two sided head then forget this

if you think you might be having trouble getting the pump all the way onto the valve
you should be using the nut that comes with most presta tubes
to keep the valve from going inside the rims

sometimes pumps are finicky about the position of the presta valve nut when you unscrew it
i have been unable to inflate some tubes with some pumps
when the presta valves were unscrewed all the way
and it was necessary to unscrew them only half way to get the tubes to inflate

OldsCOOL

I've not experienced this prob before. I was going to suggest "burping" the valve but you had done that. Replace the tube??

rpenmanparker 

Sounds like a sticky valve. Try starting from empty when there is no air pressure holding the valve shut.

Al1943

You probably just need to burp the valve again. When you saw the pressure drop from 120 to 80, that was probably the valve opening. At that point you should have been able to pump up the pressure to whatever you need. The 0, 80, 100, 120 was probably the pressure building in the hose. When it dropped to 80 the valve opened and was then reading the internal pressure. Some valves stick more than others, and when the internal pressure is already high it holds the valve closed until the external pressure is high enough to force it open.

fietsbob

the hose goes up in pressure , but is not getting past the sticky check valve in the stem.

Gage is getting the hose but the tube is still at 80, so once the valve is un stick the greater hose pressure
will overcome the lower pressure in the tube, a stroke at a time.

ClarkinHawaii

Slime or other such stuff that has hardened in the tube around the inner end of the valve can produce weirdness.

Also I once had a pinched tube that would hold pressure up to about 80 psi, but pressures over 80 were sufficient to open up the tear/hole in the tube and let air escape. That was a real head-scratcher until I took the tire off and found the tube had been pinched into a crease.

necrowinter

I was able to finally get it. I'd really like if someone can elaborate on what I'm about to say and help my figure out whats going on.

On the back tire, I loosened the valve screw thing (someone please let me know what this is called) half way this time, I put the pump on as far as I possibly could, I tried pumping it, it didnt work, so I started taking it off, I started to hear air come out, and I started pumping there.

I went on to try my front tire again, and I didnt really run into any issue, so I think theres something up with the valve on my back tire. but I'm very much a novice and I dont really know.

I'm gonna try cleaning it or something

Al1943

"Valve screw thing" is fine. We all know what you mean. It does not matter much how far you loosen it, I prefer to open it most of the way but not all the way. As I tried to explain before, it's the pump pressure that normally opens the valve. If you push on it when the nut is unscrewed partially or fully it will also open. The air pressure inside the tire and tube is what hold the valve closed. We burp the valve before installing the pump head "chuck" because the valve often becomes stuck. Burping the valve lowers the internal tire/tube pressure slightly and helps loosen a stuck valve. As you pump, the pressure from the pump should force the valve open. If not remove the pump head and burp the valve again. After pumping the tire/tube to full riding pressure screw the nut down to protect the internal stem from being accidentally bumped open or bent.
To relieve frustrations you can always replace the tube and valve but don't throw away the old one unless you are sure it's bad.

jsharr

The head on my Specialized AirTool is very finicky about how it is placed on the valve. If I am not careful, it will not open the valve and allow air into the tube. Just pressurized the hose and I get a huge reading on one stroke adn no air in tube and it is impossible to pump any more.

Play with your pump head a bit, might have something worn in there that needs to be replaced.

Al1943

There is nothing needed in the pump head to open the valve. When the pressure from the pump exceeds the pressure inside the tire and tube the valve should open, unless it's stuck. Burping the valve should unstick it.

DiabloScott

True, but sometimes you can unstick it with the pump head on the valve - I frequently have to push it on a little farther after I get hose pressure but no flow, and then it unsticks and acts normal. Burping before you put the head on sometimes isn't enough.

jsharr

Have been pumping these valves up since the 1980s with a variety of pumps. I know for a fact that if I do not get my current Specialized pump on must right, it will not inflate. Not sure of the mechanics but I know when the bike shop gave me a new head, it worked better for a bit and then back to the strangness. Thought it was worth mentioning.

dwmckee

One quick way you can confirm the pump is working correctly all of the way out to the valve stem is to put your thumb over the correct hole in the pump head and pump a stroke or two to confirm pressure builds under your thumb. If that is happening your problem has to be in the valve stem or tube. If not the problem is in the pump or pump head.

Al1943

I didn't mean to contradict what you were saying. For someone new to presta valves I think it is most helpful to understand how the thing actually works, and how very simple the presta valve mechanics are. When people unfamiliar with presta valves use pump heads designed to work on both presta and schrader valve pumps it's easy to become confused about the internal parts of the pump head and presta valve. The internal piece that pushes down to the valve is not needed for a presta valve, in fact for presta valves it will probably be more trouble free if you take it out and throw it away. It's intended use is really for pushing a schrader valve open. All you really need is an "O" ring or circular seal of some kind to seal around the outside of the presta valve stem. I prefer to use a Silca chuck which has no internal parts, only an "O" ring.

Al1943

Yes, but my comments for the OP was to emphasize the simplicity of the presta valve. Once a presta valve owner understands simple it is and how it works most of the problems will go away and whatever problem may arise will be easier to fix.

rpenmanparker 

Necessary or not, many presta chucks nowadays do depress the valve tip and obviate the problem of a stuck valve. I dealt with the simpler kind for years and years and certainly can whenever I have to. Burping the valve to get things started is pretty much second nature for folks who have been doing this for a while. Nevertheless it is really nice to have the kind of pump that eliminates that little problem for you and opens the valve as the chuck is being installed on the stem.

Hopslam

I got a bunch of specialized tubes some years back . Got a good deal , or so I thought. All of them had sticking valves just as you mentioned . Seems to be a crap shoot buying tubes anymore . Each time I buy a trusted name tube they change the valve design . Last year they even miss labeled the size on the box.
Last year got a Lenzye floor pump with the screw on attachment , it over powers the sticking valve . It takes about 160 psi to do so

cheers