preasta valve question.

MarcinG

Hi.

I'm completely confused as i used to think about myself as good mechanic (used to build wheels etc) but never worked on road bike (mtb only).
My wife recently bought road bike and asked me to inflate tires.
As all my pumps are shreder I went to argos and bought some cheap "track bike pump" with manometer etc.
I unscrewed little thing in the middle of valve and pressed it (some air escaped) to make sure that it is not stuck.
I then put adaptor over valve and closed it and this is as far as i got.. ;/
Pressure is only building up inside hose - goes up to about 8bar and then i'm unable to pump it harder but nothing goes to tube.
Is this sth wrong with pump (too weak to open the valve - maybe there is 9bar in the tube already?) or i'm doing something wrong?
Never had problems with those valves before (but i worked with hand pumps only and far less pressure in mtb tubes)
can you help me please?

robertxxx

is the little pin in the middle bent? happens to me sometimes.

aquanaut

On my track pump you can lock it either direction but only one works - lock it the wrong way and its similar to what you describe

Raam

8bar is plenty of pressure. If you really want more in, then let a load out first then start pumping. Sometimes if there is a lot of pressure already in there then the valve won't release properly and you need to let a load out first.

Holyboy

Had a customer with the same problem,couldve even been the same pump! I stripped down the whole thing and found that a little hole in the actual head of the pump was blocked,it hadnt been moulded properly,quick drill with a tiny bit and it was perfect,might not be that though!

MarcinG

thx for replying.

so:
@robertxxx

don't think so (but she is at work on bike) as i could release pressure by just touching it.

@aquanaut

it works one way only - btw does it does anything more than just fixing it tight n the valve (as in shreder you need to push it)

@Raam

i'm just totally guessing the pressure in the tube (i wanted to check it in a first place but i got problems as described).

@Holyboy

this is my one:


i even bought presta>shreder adaptor with same pump and used my topek morph mini master blaster (who named it? with no results as well.
may try pocket shock dxg tomorrow (max 300PSI) but it would take 3 days to pump bike tire with it (just use it as a pressure tester rather than pump as such).
+ i don't thing this is a case as pressure is building up ok and stays high (so pump etc ok) and releases all the air once you open lever. I'm not quite sure how it works - i mean is just air pressure pushing valve in or does the pump has to push something like in shreder?
ages ago i had very cheap small hand pump which in order to switch from presta to shreder you needed to swap entige guts upside down and can't remember anything which could posibly go wrong - is it possibe that actual pressure in the tire is already greater than abilities of the pump and this is why nothing happens? (i couldn't test it today as she was so proud to go to work on new bike that i didn't want to let her down and mess too much with it). hmm just thought how is the air directed to proper hole? i mean there are two and only one use at time?

Hermy

A problem I encountered before with a friends bike was simply that the valve stem was too short for the pump nozzle i.e. the stem didn't go far enough into the pump head to allow the tip of the valve stem to press down. Might not be relevant here though.

tomasrojo

Hermy wrote: »

A problem I encountered before with a friends bike was simply that the valve stem was too short for the pump nozzle i.e. the stem didn't go far enough into the pump head to allow the tip of the valve stem to press down. Might not be relevant here though.

I had that problem. I had to screw off the lock nut when I wanted to pump up the tyres. I eventually switched to a different brand of tube.

MarcinG

tomasrojo wrote: »

I had that problem. I had to screw off the lock nut when I wanted to pump up the tyres. I eventually switched to a different brand of tube.

ok just going back to my mothers place for holidays tomorrow i will bring my pump (i have quite big stainlesssteel "proffesional" floor pump there and if this won't help i'll buy new tubes.)
thanks guys