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I have a Blackburn entry level dual head floor pump. I usually pump up my presta valve/tires to 105 psi. I noticed that when I remove the head, some air still comes out, no matter how quickly I try to remove the pump head. I wondered how much air I am losing here, so I ran a test. After pumping to 105 psi and removing, I re-attached the pump head and locked down with the lever. No air came out at this time, however I noticed that there is no reading on the pump. I then raised the pump handle to max and depressed one time. The reading then came up to 95 psi. I am losing 10 psi by just removing the pump head? I know on a presta valve that you have to unscrew the cap and then if you press down , air will quickly escape, but is this normal for my pump not to read until I pump one time? Thanks.
 

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soy un perdedor
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Grease the oring on your pump head to make it easier to get off. You will still hear air being released when you remove the head because there is compressed air in your pump and the hose. You shouldn't be losing 10psi.

Yes it is normal for the pump not to read until you pump. The pump pressure has to reach the tire pressure first. Presta valves work like a check valve. They won't allow flow out from in the tube into the pump.

I had the exact same problem and questions years ago, so you're certainly not alone.
 

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Collin's Dad
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Yep, like RocketDog said, what you are hearing is most likely the compressed air escaping the pump hose. And also the air inside the pump hose has the overcome the pressure in the tire before it enter it so you are likely not actually pushing air on that first stroke when checking the pressure, can you hear the air enter the tube? Also if you have trouble putting air in, remove the pump head from the valve stem and hit the presta head a few blips, this'll make putting air in easier (at least it does for my pump).
 

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NO air should escape from the tire

when you remove the chuck, unless you've put it on wrong, so the valve stem is pushed in. With a presta valve, the valve is only open if the stem is mechanically moved (like when you push it to let air out) or higher pump pressure outside pushes it open, and then air flows IN. As soon as the outside pressure drops, the greater pressure inside the tire pushes the valve closed again. As the other posters said, you're probably only hearing the air escaping from the pump body, where some pressure remains. You probably have nothing to worry about.
 

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Fini les ecrase-"manets"!
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RocketDog said:
Yes it is normal for the pump not to read until you pump. The pump pressure has to reach the tire pressure first. Presta valves work like a check valve. They won't allow flow out from in the tube into the pump.

I had the exact same problem and questions years ago, so you're certainly not alone.
On my pump, you can hear a difference between just pumping up pressure in the pump hose and actually putting air in the tire. You can hear the valve working, and the air going into the tire. You can also watch the needle--it goes up REAL fast and is very steady when you're filling the hose, but when you're filling the tire, the pressure goes up slower (more volume to fill), and will ease a little after you finish each pump stroke (due to the release into the tire of excess hose pressure required to open the valve).

Pump until the guage reads the pressure you want--unless your valve is really sticky (and you ought to give it a tap to make sure it's loose before you pump), you'll be within a pound or so of your desired pressure no matter what.

This is the big advantage of presta valves--it's hard to lose pressure back out of them when removing the pump head. The scary part about them is that rush of air back out of the hose when you pull it off. If you don't know what it is, well, you think what you thought. But if you DO know what it is, it's still stressful, because it's very similar to the sound made when you rip the valve stem out of your tube with the pump head. DAMHIKT (Don't Ask Me How I Know This).
 

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Arrogant roadie.....
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dbmcclus said:
I have a Blackburn entry level dual head floor pump. I usually pump up my presta valve/tires to 105 psi. I noticed that when I remove the head, some air still comes out, no matter how quickly I try to remove the pump head.
That's because the tire and the hose are all at 105 psig, until you break the seal around the stem. no surprise there.

I wondered how much air I am losing here
From the tire-nothing.
From the hose-everything. Next question??
so I ran a test. After pumping to 105 psi and removing, I re-attached the pump head and locked down with the lever. No air came out at this time, however I noticed that there is no reading on the pump.
That's because the pressure in the hose is atmospheric pressure. What were you expecting??
I then raised the pump handle to max and depressed one time. The reading then came up to 95 psi. I am losing 10 psi by just removing the pump head?
No. since the pressure in the hose is still less than inside the tire, the valve won't open. It works with pressure only. Take a course in physics or chemistry...

I know on a presta valve that you have to unscrew the cap and then if you press down , air will quickly escape, but is this normal for my pump not to read until I pump one time? Thanks.
Yes it is. You obviously have no idea about how a presta valve works. Take one apart.
 

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I assume that's why this was posted in the beginner's corner :/ As a beginner myself, I'm not entirely sure how they work either, but thanks for the explanation.
 

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Discussion Starter #8
This is for Dave

As ImNag stated, this is a beginner's forum!

Dave, you are correct. I do not know how presta valves work. That is why I am asking. I am a beginner. Your comments were very informative, but not tactfully written. You might try being a little nicer to someone that is new. I am thicked skin, so I will stay tuned to this forum. Others may take offense and not come back.

Thank you again for the good info.
 

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Make sure you are getting the presta valve to open. Most of mine stick. So before I pump, I unscrew the valve and then push it in until some air escapes. Just a quick "psst". Then I connect the pump hose and pump. If you listen closely, you can hear the valve click open as the air pressure in the pump reaches the same pressure as the air in the tire. If the valve doesn't open, then the psi reading on the pump will go very high after only a few pumps, since you are pressurizing only the hose and not the tire. Either way when you take the hose off the valve, the air remaining in the hose will come out since the head on the hose does not close the hose off like the fitting for a car-type schrader valve usually does.

Don't forget to screw the presta valve closed when you are done. It doesn't have to be tight, just closed.
 
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