# Trick to using a shock pump?



## getagrip (Mar 26, 2008)

Got my first shock pump for an air fork. When I put air into the fork, I can see that the air pressure increases. However, when I unscrew the valve to detach the pump, the pressure decreases, so I'm basically back where I started. What am I missing? If it helps, I have this model below:

Fox Shox HP Pump > Accessories > Inflation > Shock Pumps | Jenson USA Online Bike Shop


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## Le Duke (Mar 23, 2009)

Not trying to be an ass, but the valves on your fork, your tires, a car tire, etc. all work the same way. The air is not escaping from your fork; the valves on your fork CLOSE after each pump stroke.

That's air escaping from the pump. Not your fork.


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## jeffj (Jan 13, 2004)

Try only screwing the pump connector on maybe a half turn past where pressure shows on the gauge. Then, when you go to unscrew it, give it a quick turn and you should hear a very tiny, very quick "pssst" and you'll lose almost nothing. If you screw the connector all the way on, you won't know when you get to that point when the air will escape and it could be right when you have to regrip the connector between turns.

Topeak makes an adapter that helps combat this problem. Used correctly, they do a decent job of it too:

Topeak® Cycling Accessories ? Products - Pressure-Rite

This pump has one built into it:

Topeak® Cycling Accessories ? Products - PocketShock DXG


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## getagrip (Mar 26, 2008)

jeffj said:


> Try only screwing the pump connector on maybe a half turn past where pressure shows on the gauge. Then, when you go to unscrew it, give it a quick turn and you should hear a very tiny, very quick "pssst" and you'll lose almost nothing. If you screw the connector all the way on, you won't know when you get to that point when the air will escape and it could be right when you have to regrip the connector between turns.
> 
> Topeak makes an adapter that helps combat this problem. Used correctly, they do a decent job of it too:
> 
> ...


Thanks Jeff!


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## zebrahum (Jun 29, 2005)

Le Duke said:


> That's air escaping from the pump. Not your fork.


It's this.

Schrader valves are spring loaded, they close as soon as there is a pressure differential between the tube and the hose so when you unscrew the valve, as long as you're not unscrewing it very slowly, the spring closes the valve. The air you hear is air in the hose and pump body.

The air chambers on suspension are very small volumes so when you attach a pump to a shock you will lose around 5-15 psi just by attaching the pump. That's why you always write down your pressure setting instead of just putting another 5 psi in if it doesn't feel good; if you always put 5 more psi than is showing on the pump then you wouldn't get anywhere because every time you put the pump on you lose 5+ psi.


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## Slash5 (Nov 27, 2011)

Le Duke said:


> Not trying to be an ass, but the valves on your fork, your tires, a car tire, etc. all work the same way. The air is not escaping from your fork; the valves on your fork CLOSE after each pump stroke.
> 
> That's air escaping from the pump. Not your fork.


That's true of presta valves but not schrader valves. The adapter used on schrader valves pushes the pin in so all of the air could escape.
From Wikipedia:
Another disadvantage of the Schrader is that the air chuck must depress the spring-loaded pin before air can flow during inflation, whereas the Presta valve relies solely on internal air pressure to keep it shut. This means that some air is lost while attaching and detaching pumps to Schrader valves, although this is usually nominal.

Shock pumps usually use a long attachment adapter so that by the time the adapter has been unscrewed enough for air to escape, the schrader valve pin is no longer depressed. The air that escapes is only from the pump, not the shock.


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## eb1888 (Jan 27, 2012)

The valve on your shock or fork, if a shraeder has a removeable core. Sometimes the seal in this goes and the core needs to be unscrewed and another on installed. Check it with some soapt water. Tire stores have the cores all over the floor or bins by the mounting machine.


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## theMeat (Jan 5, 2010)

getagrip said:


> Got my first shock pump for an air fork. When I put air into the fork, I can see that the air pressure increases. However, when I unscrew the valve to detach the pump, the pressure decreases, so I'm basically back where I started. What am I missing? If it helps, I have this model below:
> 
> Fox Shox HP Pump > Accessories > Inflation > Shock Pumps | Jenson USA Online Bike Shop


I'd been filling shocks for years without much of an issue, sometimes having to use the technique jeffj ^ refers to, then I put a new shock on my bike and could not get air to stay in for nothing. I searched the web, tried and tried again then finally gave up and brought it into my lbs for some help. When the mechanic had the same issue we tried a pump with a 2 stage disconnect and wala. The end of the hose has 2 screws, one for the pin that holds the shock's pressure, and one for the threads on the valve as all shock pumps have.
I bought a Sette Air 2 st 35 and have no complaints, but companies like Avenir and others make them too.


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## Shibby (Jan 13, 2004)

Yep - most pumps that have this feature will advertise it as well. might be called 2-stage or no-leak or something similar. Doesn't necessarily have to have 2 screws - mine just has a long valve attachment. It disengages the valve pin prior to the seal being broken between the valve and the hose.


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## theMeat (Jan 5, 2010)

Le Duke said:


> the valves on your fork CLOSE after each pump stroke


Not trying to be an ass but NO, it's not, hence the problem, then solutions, this place rocks


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