Floor pump releases 15 psi when removing hose from valve! (normal?)

Is this normal? I have presta valves. When I take the hose off , I hear the
big pssst . My tires call for 125 psi max. I put 120 in. But I check the
tire with 2 different gauges. They both read 105 psi. Should I overinflate
it to make up the difference that I am losing? Or do I have a bad pump? My
friend says he doesn't have this problem. Thanks a lot

"chrisc" wrote:

Is this normal? I have presta valves. When I take the hose off , I hear the
big pssst . My tires call for 125 psi max. I put 120 in. But I check the
tire with 2 different gauges. They both read 105 psi. Should I overinflate
it to make up the difference that I am losing? Or do I have a bad pump? My
friend says he doesn't have this problem. Thanks a lot

The big pssst you hear is air escaping from the pump. It's not from the
tire, or more accurately the tube, because the valve shuts as soon as
the outside pressure is less than the pressure inside the tube.

You say that you have inflated to 120 psi, and I assume you read that on
the pump's gauge. If two different pressure gauges agree on 105 psi,
I'd be inclined to believe that rather than what the pump says. In any
case, removing the chuck will not lose 15 psi worth of air unless there
is something preventing the valve from closing quickly.

All bets are off if you are inflating the tire in a full vacuum. When
you bring the tire back into the atmosphere, the relative pressure is
reduced by 15 psi from 120 to 105.

--
Ted Bennett

"Ted Bennett" wrote: (clip) If two different pressure gauges agree on 105
psi, I'd be inclined to believe that rather than what the pump says.
^^^^^^^^^^^^^
What Ted says is most likely--pump gauge reads high. One way to check this
is:

1.) Pump tire up to a known value on the pump gauge.
2.) Remove pump connection and check tire pressure with your hand-held
guage. (According to your past experience, this will be 15 psi low.)
3.) Carefully reattach hose and give the pump a stroke (or two), watching
the gauge.

If the pump is wasting 15 psi on removal of the connector, you will see that
when you do step 3, above. If the pump gauge is reading high, you will
still have approximately the same pressure as when you finished step 1.

BTW, when I have tried to pump up my tires in a vacuum, I have encountered
two problems: I get out of breath really fast. And, my pump doesn't work.
;-)

What do you mean by pumping them in a vacuum? Sorry to be so _________.
Thanks again

"Ted Bennett" wrote in message
...
"chrisc" wrote:

Is this normal? I have presta valves. When I take the hose off , I hear
the
big pssst . My tires call for 125 psi max. I put 120 in. But I check the
tire with 2 different gauges. They both read 105 psi. Should I
overinflate
it to make up the difference that I am losing? Or do I have a bad pump?
My
friend says he doesn't have this problem. Thanks a lot

The big pssst you hear is air escaping from the pump. It's not from the
tire, or more accurately the tube, because the valve shuts as soon as
the outside pressure is less than the pressure inside the tube.

You say that you have inflated to 120 psi, and I assume you read that on
the pump's gauge. If two different pressure gauges agree on 105 psi,
I'd be inclined to believe that rather than what the pump says. In any
case, removing the chuck will not lose 15 psi worth of air unless there
is something preventing the valve from closing quickly.

All bets are off if you are inflating the tire in a full vacuum. When
you bring the tire back into the atmosphere, the relative pressure is
reduced by 15 psi from 120 to 105.

--
Ted Bennett

chrisc wrote:

I have presta valves. When I take the hose off , I hear the big pssst . My tires call for 125 psi max. I put 120 in. But I check the tire with 2 different gauges. They both read 105 psi. Should I overinflate it to make up the difference that I am losing? Or do I have a bad pump?

If two gauges read the same, they're probably right. Either the pump's
gauge is off by 15 psi, or you're losing air when removing the pump
head.

What kind of pump are you using? It's best to use a good floor pump
with a Silca brass presta head. See:
http://www.sheldonbrown.com/harris/tools-h-z.html#pump

Try to borrow a known good pump and compare its readings to your pump.
If it turns out that your gauge is off by 15 psi, you can either pump
until it read 15 psi higher than you want, or try to reposition the
pointer.

Does your pump indicate "0" when not in use? If not, that's your
problem.

Art Harris

Leo Lichtman wrote:


BTW, when I have tried to pump up my tires in a vacuum, I have encountered
two problems: I get out of breath really fast. And, my pump doesn't work.
;-)



Another reason to go with CO2 carts. ;-)

It's a Avenir floor pump. It does read 0. I'll try a friends pump.

"Art Harris" wrote in message
oups.com...
chrisc wrote:

I have presta valves. When I take the hose off , I hear the big pssst .
My tires call for 125 psi max. I put 120 in. But I check the tire with 2
different gauges. They both read 105 psi. Should I overinflate it to make up
the difference that I am losing? Or do I have a bad pump?

If two gauges read the same, they're probably right. Either the pump's
gauge is off by 15 psi, or you're losing air when removing the pump
head.

What kind of pump are you using? It's best to use a good floor pump
with a Silca brass presta head. See:
http://www.sheldonbrown.com/harris/tools-h-z.html#pump

Try to borrow a known good pump and compare its readings to your pump.
If it turns out that your gauge is off by 15 psi, you can either pump
until it read 15 psi higher than you want, or try to reposition the
pointer.

Does your pump indicate "0" when not in use? If not, that's your
problem.

Art Harris