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Old 15th August 2014, 12:21 PM
hodge hodge is offline
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Default Leaking AA400

Discovered today that my S400 is leaking air directly after a refill. Cannot hear the air escaping. Would anybody out there have any idea of possible causes and cures?

Thank you

John Hodgetts

The Dog Wizard.
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Old 15th August 2014, 12:42 PM
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LittleJack LittleJack is offline
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Fill it up again and stick a balloon over the filler cap. Thats how I found mine once. Also if its been serviced recently I believe there is an o-ring that sits between the breach and the trigger mech or something like that, if that has not been re-fitted it will leak!
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Old 15th August 2014, 01:11 PM
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Is it one of those 400s that has a pressure relief valve built into the front cylinder plug? You can tell by the little weep hole drilled radially into the flange part of the plug.

When these fail, they usually vent the top part of a refill then stick at say 160 bar and "heal up" until you fill again. They are meant to blow off at about 200 bar to prevent over-pressure in the cylinder but the O rings go hard after a while.

I've only got one 400 left with this device in it; all the rest I've changed the front plug and done away with them completely. They were never a standard fitment.

Other sources of leaks are the filler itself if it's the pointed type, the earlier one. More rarely the O ring under the block that carries the pressure gauge is at fault. If it's an AT rifle it's a beggar to fix too.
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Old 15th August 2014, 01:29 PM
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Tench Tench is online now
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The old style bayonet filler is notorious for leaking, it rusts inside preventing the o ring from sealing, I have tried to fix these but they are not worth the trouble, just replace it and also the dowty washer behind it. The pressure gauge is also sometimes at fault, check the little vent hole on the side of it. or as was mentioned above the very thin section o ring 6x1mm under the gauge mounting block. These are the easy fix external leaks, a leak anywhere else will require the rifle to be stripped.
Use some bubble solution to help you find the leak, 50:50 washing up liquid and water.
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Old 15th August 2014, 01:31 PM
Akita Akita is offline
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You can also put a ballon over the barrel with the bolt close to see if the firing valve is leaking.
Also the small oring between the pressure gauges ally dogleg and the action put water with a tiny drop of washing up liquid around it to see if theres any bubbles.
Clean up the residue though as washing up liquid can rust things if left.
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Old 15th August 2014, 01:39 PM
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chrisc chrisc is offline
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Mostly covered by the knowledgeable gents above.

3 common place for leaks on the S4** series are..
Firing valve not seating properly
o ring under pressure guage.

The balloon thing is a good way to find out where the leak is. Place over the filler and see if it inflates. If not then place over the barrel (with breech closed) and see if it inflates. If it inflates on the barrel then it's a good bet that the fiirig valve is not sealing. If neither the barrel or filler inflates the balloon then it's the pressure guage and could just need 'nipping' tight. Normally replacing the o ring will stop the pressure guage leak.

you can get spares from Julian Bond or best fittings....or even Air Arms if money is no object

If you PM me your email address i have a s400 strip guide showing the rifle stripped to it's guts. It's an older s400 but virtually identical inside.

Last edited by chrisc; 15th August 2014 at 01:44 PM.
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Old 15th August 2014, 02:09 PM
hodge hodge is offline
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Default Aa400

Thank you for all of the advice I will try to locate the source of the leak by the methods suggested.

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