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Thread: S400 Classic 0.177 broken Firing Valve P/N S370.

  1. #1
    Sharp Shooter

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    Default S400 Classic 0.177 broken Firing Valve P/N S370.

    I've been lost and found, like the walk-away-son in the Bible
    My Air Arms S400 Classic was unused for years and last week I got my new filled scuba tank at 300 Bar.
    On the first try it would not fill the S400, you could hear air blowing as if it was coming out of all seals.
    I opened the cylinder quickly and released the line pressure just as quickly to try and let the seals do their job.
    Silence filled the little room, no leaks, but the S400 was little over pressured at 200 Bar, maybe 250 Bar.
    I started shooting, lowering the pressure shot by shot and this morning it was a perfect 150 Bar.
    One shot and then all the pressure bled out.
    Disassembling it proofed to be a broken Firing Valve P/N # S370 on the owners Manual.

    If you read my story this far you would probably bear with me for the rest,

    The valve is made out of a steel rod with a bakelite, like bit on the end and that is the only seal that keeps the pressure in the tube, away from all the rest. When then trigger is pulled it strikes the rod on the far end and opens this 'bakelite' seal to open for a millisecond to let the air out behind the pellet, but made out of such hard material, how can it properly seal again.

    I need a new P/N s370 and all other seals to make the riffle perfect again.

    Regulated valves quotes will be appreciated

    Warm Regards

    Swannie
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  2. #2
    Sharp Shooter
    The Professor

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    The material is not bakelite, rather a high strength plastic, although I don't know exactly which type AA currently use.

    The material needs to be hard to avoid deformation of the very narrow sealing lip.

    I have made replacement valve heads in the past turning them on a lathe out of Nylon 6 and re-using the original steel stems.
    Last edited by Dale; 15-08-17 at 15:23.
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  3. #3
    Sharp Shooter
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    On that topic my AA410 Carbine made a leaking whoosh sound when I pulled the trigger and since then there seems to be no air released when I cock and release trigger although there is 150bar in the silinder. What could the cause be?
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  4. #4
    SAFTAA FT Colours '15
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    Quote Originally Posted by DSF View Post
    On that topic my AA410 Carbine made a leaking whoosh sound when I pulled the trigger and since then there seems to be no air released when I cock and release trigger although there is 150bar in the silinder. What could the cause be?
    My diagnose is dit is gebreek.
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  5. #5
    Sharp Shooter
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    Jinne maar jy is slim, jy moes twee gewees het!
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  6. #6
    Sharp Shooter

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    On Swannie's note.

    Could this happen because you overfilled the rifle?
    According to AirArms the S400 rifle should be filled no more than 190Bar. I do believe that they have tested a higher filling pressure, but 250bar is almost 30% more fill pressure than they warn against.
    I am sure it will not break because of that. If any I think the seals of the cylinder will go first.
    Maybe all the extra pressure and already weakened part inside (P/N s370) was just what it needed to break.
    I really hope you can replace this part and continue to enjoy your S400.
    Please keep us updated.

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  7. #7
    Sharp Shooter
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    Quote Originally Posted by DSF View Post
    On that topic my AA410 Carbine made a leaking whoosh sound when I pulled the trigger and since then there seems to be no air released when I cock and release trigger although there is 150bar in the silinder. What could the cause be?
    This might sound like a silly question but are you looking at the gauge fitted to the rifle to ascertain there is air in it?

    I have seen these gauges stick and give wildly false readings, so there is a possibility your whooshing sound was the rifle dumping its remaining air because the pressure was much lower than the gauge indicated and the hammer was able to hold the valve open.
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  8. #8
    Sharp Shooter

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    Hi guys
    Dale the correct material to use for a PCP valve is called acetal, it is easy to turn with a sharp cutting bit.
    I repaired a S400 a while back, I also reused the original valve stem, and made a new valve head from acetal. It is critical to produce a valve that is exactly the same dimensions as the original one as it affects the power of the rifle if the length differs.
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  9. #9
    Sharp Shooter
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    Quote Originally Posted by Dale View Post
    This might sound like a silly question but are you looking at the gauge fitted to the rifle to ascertain there is air in it?

    I have seen these gauges stick and give wildly false readings, so there is a possibility your whooshing sound was the rifle dumping its remaining air because the pressure was much lower than the gauge indicated and the hammer was able to hold the valve open.
    Spot on Dale. The nanometer needle seems to be stuck somewhere between 130-150bar mark. I connected my filling station and the filling station gauge showed zero pressure. So that whooshing sound was indeed the carbine dumping its last breath while the nanometer show different. I filled it to 180bar to test for leaks and found none, the carbine happily digested a few dozen pellets and accurate as ever. Guess I am due for a gauge replacement on my oldest Air Arms then.
    Still on that topic another AA in the house of almost the same age is leaking air out the loading port with pressure above 50bar. I assume/hope seal replacement on loading port is all that is needed?
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  10. #10
    Sharp Shooter
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    Quote Originally Posted by DSF View Post
    Still on that topic another AA in the house of almost the same age is leaking air out the loading port with pressure above 50bar. I assume/hope seal replacement on loading port is all that is needed?
    For this to happen suggests a problem with the firing valve not sealing correctly, could be something as simple as a bit of muck on the valve seat. It would need to be stripped and inspected to find the cause though.
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  11. #11
    Sharp Shooter
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    What a player Dale, I've learnt a good bit from you following this thread and thanks to you I've got decent triggers in my Walthers, thanks for sharing your wisdom.
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