how to check pressure in presta tubes?

MarcinG

Hi.

I have floor pump with manometer but in my opinion it only shows pressure inside hose (presta valves) rather than inside tube
Same with digital manometers - even buying presta>shreder adaptor doesn't change it at all.
It all works fine with shreder as every time you measure it the valve is open but this isn't the case for presta.
How do you chceck yours? I wouldn't bother at all for MTB but IMO in road bike it is quite important factor.

coastwatch

The gauge on the pump should work, are you sure you're opening the screw on the presta valve before checking / pumping?

MarcinG

coastwatch wrote: »

The gauge on the pump should work, are you sure you're opening the screw on the presta valve before checking / pumping?

of course.

On presta pump is not opening valve.
So if pressure is lower at the outside side of the valve (most cases apart from pumping) valve remains closed (unless you press it by finger).
So while you pumping gauge on your pump shows you pressure inside the hose especially when it is lower than pressure inside tube.
After longer thought i may say that when pressure shown by pump is either smaller or roughly equal to pressure inside tube - but how to check pressure with digital gauge? I think you can't.

Lumen

Assuming a working presta valve, if the pressure was higher outside of the valve the valve would open.

So the gauge reading is always lower than or equal to that inside the tyre, to a reasonable degree of accuracy.

I have no way of proving this as I'm too big to fit inside the inner tube.

coastwatch

MarcinG wrote: »

of course.

On presta pump is not opening valve.

I think you might be better off getting a proper track pump (with gauge)
I have a track pump, when you attach the hose, the fitting (presta type) opens the presta valve and keeps it open. The pressure reading on the gauge is the pressure in the tube. There must be a non-return valve somewhere because the pump doesn't "inflate" when you stop pumping.

Your digital pressure gauge might be for Schrader valves only and might not work with presta, even with the attachment fitted. If you really wanted a digital pressure gauge for bikes , ie Presta & Schrader valves, you might be better off with one of these, but I think a proper track pump would be a better investment.

tomasrojo

I don't think track pumps are set up to keep presta valves open while the chuck is in position. My understanding is that the pumping action forces air down the hose, and the rise in pressure opens the valve and forces air into the tube; at the conclusion of the downward stroke of the pump, the pressure in the hose drops and the presta valve closes, with the pressure in the hose and the tube about equal.

As Lumen said, in other words.

victorcarrera

I can only comment on floor pumps that do not automatically open the presta valve when it is connected.
Over time valves will stick so this is why you should always free it and let a little air out before you start. Then pump until you hear the valve inner clicking in sympathy with the pumping action. An accurate guage should now indicate the pressure inside the tube + approx 5psi to overcome the valve inner opening inertia and when you reduce the weight on the pump it should indicate the tube pressure - the valve inner closing inertia. My Lidil pumps are not accurate enough to show the difference as they seem to latch every 10psi or so. But this could be a deliberate too.

tomasrojo

Does a discrepancy of a few psi or a few dozen millibars or whatever you use yourself really matter?

el tel

Am pretty sure there was a comprehensive thtrad on this subject befire.

My advice is to let some air out of the tube before attaching the the pump attachment then pump like a bastard for as long as you are able but stop two or three strokes before the tube explodes.

MarcinG

tomasrojo wrote: »

Does a discrepancy of a few psi or a few dozen millibars or whatever you use yourself really matter?

it doesn't.
I just never had a road bike before and had no idea what sort of pressure is right for it apart from what it says on tire and to match it i needed a gauge.
My previous lidl pump was totaly inaccurate (tested with digital gauge on mtb tube once).
i bought new pump (lidl one broke) to new bike (all my previous bikes were mtb - shreder) so i soon realized 2 things:
pressure building up in the hose (well with bit of thinking i finally got to right conclusion that it is roughly equal to pressure in tube)
how do i know is the new pump right? (went to bike shop and guy sold me shredder>presta adaptor to my digital gauge which i couldn't use hence 2nd part of the question).

So i guess all i need is shreder tube to check gauge on pump and i'll be fine (in worst case will mark inaccuracy level on pumps gauge).

thans all.

manwithaplan

el tel wrote: »

stop two or three strokes before the tube explodes.

The best way to find this point is to wait for the tube to explode and go back a couple of strokes.

smacl

manwithaplan wrote: »

The best way to find this point is to wait for the tube to explode and go back a couple of strokes.

Tried this recently and didn't go quite as planned. Helluva bang mind you, accompanied by the sound of a breaking wine glass (herself) and streak of white fur leaving the garden (cat). This was at the 120psi mark on the JoeBlow, which I no longer fully trust, and now leave the tires at 100/110 front/back.

coastwatch

coastwatch wrote: »

...
I have a track pump, when you attach the hose, the fitting (presta type) opens the presta valve and keeps it open. The pressure reading on the gauge is the pressure in the tube.

It turns out that was a little bit of BS from me . Following a few "kitchen tests" I can confirm the valve does indeed close between pump strokes, so it as victorcarrera says. And I thought I had a special pump...

billy.fish

Lick it.

Cee-Jay-Cee

Bumping this as i need some help inflating mine also.

I bought one of the double cylinder foot pumps in Aldi (rated to 140psi) The tyres have max inflation of 110psi. The valves are short type (40mm maybe) and i had to deflate the tyre entirely in order to pump it up again but i cannot get the damn thing any harder than 70/80psi.

Should the gauge on pump show the pressure in the tube constantly or will it only show the pressure on each pump?

Would it be easier with a longer valve (80/100mm)?? Or would it be simpler with a shrader adaptor on the valve and then use the shrader end on the pump hose?

doozerie

@CJC99, The gauge on the pump should show the pressure in the tube constantly. However, it'll only show an accurate measure once the pressure in the pump hose is enough to open the valve in the tube at least once - until that point it may show a pressure reading which is too high (where the valve is perhaps too stiff for the pump pressure to open it despite the pump host pressure being higher than the pressure inside the tube) or too low (where the pressure in the hose is not enough to push against the pressure exerted on the valve from inside the tube).

And whatever about the theory, the pressure gauges on some pumps are simply muck and never accurate or consistent. That may or may not be the issue you are encountering.

MarcinG

CJC999 wrote: »

Should the gauge on pump show the pressure in the tube constantly or will it only show the pressure on each pump?

Constantly after first couple of strokes. As pressure "left" inside pump is roughly equal to pressure inside tube so once it is greater it will force valve to open.

Would it be easier with a longer valve (80/100mm)?? Or would it be simpler with a shrader adaptor on the valve and then use the shrader end on the pump hose?

I don't see how you could possibly get bigger pressure with longer valve.
Or shredder attachment.

First thing i would do is to check pressure gauge on your pump (in bike shop compare it with some good pump or on bike/car with shreder valve compare it with digital gauge. My first pump was cheap lidl/aldi and it wasn't most accurate tool;)

secman

Never used a guage, always relied on flicking the tyre with my finger, hear the "ping" its fine !


Secman

jinkypolly

CJC999 wrote: »

Bumping this as i need some help inflating mine also.

I bought one of the double cylinder foot pumps in Aldi (rated to 140psi) The tyres have max inflation of 110psi. The valves are short type (40mm maybe) and i had to deflate the tyre entirely in order to pump it up again but i cannot get the damn thing any harder than 70/80psi.

Should the gauge on pump show the pressure in the tube constantly or will it only show the pressure on each pump?

Would it be easier with a longer valve (80/100mm)?? Or would it be simpler with a shrader adaptor on the valve and then use the shrader end on the pump hose?

Sounds like the pump is not performing.

Cee-Jay-Cee

jinkypolly wrote: »

Sounds like the pump is not performing.

Yeah I'm starting to think that too.

The reason I asked about longer valve is I thought maybe I'd get a better 'attachment' with one but possibly not.

I think I'll invest in good track pump.

GreeBo

CJC999 wrote: »

Bumping this as i need some help inflating mine also.

I bought one of the double cylinder foot pumps in Aldi (rated to 140psi) The tyres have max inflation of 110psi. The valves are short type (40mm maybe) and i had to deflate the tyre entirely in order to pump it up again but i cannot get the damn thing any harder than 70/80psi.

Should the gauge on pump show the pressure in the tube constantly or will it only show the pressure on each pump?

Would it be easier with a longer valve (80/100mm)?? Or would it be simpler with a shrader adaptor on the valve and then use the shrader end on the pump hose?

Usually means you are just inflating the hose and not the tyre at all.
If you are using an adaptor make sure you have it fully screwed down.

Cee-Jay-Cee

No its not an adaptor, its an Aldi pump with the correct presta valve type head on it.

GreeBo

CJC999 wrote: »

No its not an adaptor, its an Aldi pump with the correct presta valve type head on it.

Then I would just make sure that the head is fully down on the valve, I had a similar issue with a foot pump before that never got above 80psi and I discovered it was because of the above.