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I believe that either the schrader adapter I'm using is too long or the pin for the presta core isn't long enough for me to be able to use an air compressor. It works fine with a floor pump since a pin doesn't need to be engaged for air to come out. But in my situation of trying to seat a new tire, a pump won't work. I've been searches to see if there are other valve stem adapters that allow this.

  • If you have a CO2 cartridge, you could seat it quickly with that. – Batman Dec 16 '16 at 18:55
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    You do not need to press in the pin of a Presta valve to inflate the tire. Air pressure through the chuck will press the pin in, if the little knobbie on top has been unscrewed first. There is no spring in a Presta valve -- it is only air pressure that holds it closed. So any external pressure greater than the internal pressure will open the valve. – Daniel R Hicks Dec 16 '16 at 18:58
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    Pressure is what pushes down the presta pin. Loosen the presta valve, give it a tap to ensure it is moving freely, add the Schrader adapter, then use the compressor. @DanielRHicks - you beat me by seconds! Nicely done. – Rider_X Dec 16 '16 at 18:59
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    (One common defect of Presta adapters is that the Schrader end is too short, such that the chuck will not effectively lock onto the adapter.) – Daniel R Hicks Dec 16 '16 at 19:00
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    The longer ones don't seat/seal well in the generic compressor heads (like the first one pictured below in Robo's answer. We sell many different ones and and field complaints about the Zefal adapters quite frequently. They work fine in floor pumps but have issues with compressor heads. – Nate W Dec 19 '16 at 15:51
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You're using the wrong inflator valve on your compressor.

You're likely using this type of inflator valve (aka chuck). It requires the inner pin of the schrader valve of the tire to depress the inner pin of the chuck for the chuck to release air:

Inflator valve

Instead you need one of these types of inflator valves which have a manually activated release mechanism (the lever or trigger). The advantage of these types is that they often have a built-in pressure gauge, such as the model on the right. The gauges are not very accurate but are sufficient for eyeballing pressure.

Inflator valves

If the valve on your compressor is not replaceable (because it's not your compressor, for example) then you can fill up a portable air tank with the compressor (these tanks have schrader valves) and then hook up your manual-style shrader valve inflator to them. This is also a way to use a tiny little 12VDC electric tire inflator (such as in emergency kits) to build up enough pressure and air reserves to set tubeless tires. It might take an hour to build up 5 gallons at 135psi (and you might burn out a tiny compressor, so you'd take it in chunks) but you'd have enough air to certainly set even a car tire.

[Portable air tank[3]

Note that this tank has the type of schrader valve outlet that you don't want, but you can easily swap it out.

  • Good point -- the problem is not with the valve or adapter, but with the air chuck. The type in your first picture will not release air until it's center pin has been pressed in. – Daniel R Hicks Dec 17 '16 at 19:29
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    And, oddly, even though all you need to rectify this situation is a short hose with a Presta chuck on one end and a Schrader valve jammed into the other end, such adapters do not appear to be made. – Daniel R Hicks Dec 17 '16 at 19:38
  • This is exactly my point Daniel. I don't get the gist of your first comment. – RoboKaren Dec 17 '16 at 22:46
  • You can edit for clarification but I thought I was saying what you were saying. – RoboKaren Dec 17 '16 at 22:46
  • I was just restating what you said, hoping to make clearer that the problem is the center pin of the chuck. – Daniel R Hicks Dec 17 '16 at 22:49
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It's possible the Presta/Schrader adapter is too long, I've come across a few steel finished ones a whole mil too long. The brass finished ones have always worked for me, but I'd still compare length if you can get to a bike or auto parts store. Likely easier to buy one than file the adapter you already have or putting something big enough to not damage the Presta head but small enough to not bite the inside of the adapter, like a smooth pebble, or a ball bearing. Just make sure the Presta head is unscrewed enough to not bend the threaded part, and don't put so much pressure as to snap it off in there.

Some gas station compressors need to register air pressure already in the line before it will add pressure to that line. Blowing air into the tube (sounds like you're seating a tubeless tire) likely won't be enough. Once I quickly "filled" my car tire with air to fill the line with pressure, then immediately pushed the chuck onto the totally flat bicycle tube valve.

  • Good point about the empty line. Many of the electric air meters here have a "from flat" button for exactly this purpose. – Criggie Dec 17 '16 at 8:06
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    How can the adapter be "too long"? – Daniel R Hicks Dec 17 '16 at 12:43
  • If the adapter is too long the presta valve pin wont depress the pin in the center of the air chuck. – Mark Dec 27 '16 at 2:59
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YOU DO NOT NEED TO PRESS IN THE PRESTA PIN IN ORDER TO INFLATE THE TIRE!! AIR PRESSURE DOES IT, IF THE KNOB HAS BEEN UNSCREWED AND THE PIN PRESSED ONCE WITH YOUR FINGER, TO LOOSEN IT UP.

(Though you do need to somehow get air to come out of the Schrader chuck that's attached to the compressor, and some designs are not convenient in this regard.)

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    Why the SHOUTING? – andy256 Dec 18 '16 at 7:15
  • @andy256 - Because no one was listening. – Daniel R Hicks Dec 18 '16 at 20:19
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I think it has been established that the type of chuck you're using, needs the pin of an actual Schrader valve to press the center pin of the chuck for the chuck to release air. If it's not acceptable to replace the chuck, try this - connect the Schrader adapter to a Schrader extender (available in auto parts stores... I recommend the all metal variety) and install this onto the presta valve. The pin in the extender may allow the chuck to release air. Something like these: enter image description here

  • Can you include a photo or diagram? – RoboKaren Dec 18 '16 at 7:06
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Another option is to "help" the tubeless tyre seat by using a cargo strap/motorcycle tiedown/ratchet strop around the rolling circumference of the tyre. Its a farm trick, but works okay on larger bike tyres.

enter image description here

This is a small tractor tyre having the same fix done to seat the bead while inflating.

On a bike tyre you might need to use tape to hold the strap in place - most other vehicles have a flatter profile for the strap to rest on.

  • Sometimes this is linked to a related dirty hack that involves using lighter fuel or something equally combustible, to provide a flash of expansion and seat the tyre. Don't do this, its silly and dangerous. – Criggie Dec 17 '16 at 8:16
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    Starting fluid (ether) is what I've seen used. (Though not on a bike tire.) – Daniel R Hicks Dec 17 '16 at 12:41

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