Walther venting

Discussion in 'General Airgun Chat' started by Ratinator, May 1, 2014.

  1. Ratinator

    Ratinator 77.74

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    Some help needed guys,when i shoot my domi there is a small amount of air coming out of the dry fire switch is this normal?
    If someone could run a few shots through their domi for me to check as it may have gone unnoticed before.
    Thanks Simon
     
  2. sven

    sven Member

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    Hi Simon,

    No worries, that's normal. It is the air that the hammer pushes away on its move towards the valve.

    Sven.
     
  3. hmangphilly

    hmangphilly The Doctor

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    mate , that's spooky.
    I noticed the very same thing happening last week.

    The explanation you have from the lovely Sven is the same as the one I got from the equally lovely Scooby.

    hence I'm not worrying about it :)

    regards
    phil

    ps.
    of course if its coming out if there with the gun cocked and a pellet in the breech before firing......that's a different thing.
    but I don't think that's what you've got.
    just air displacement from the hammer / piston.......it's got go somewhere
     
    Last edited: May 1, 2014
  4. RobF

    RobF Administrator Staff Member

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    Yep, the transfer port isn't sealed behind the knock open valve, so air can pass along side it it into where there hammer is and out through the unsealed dry fire switch.
     
  5. Ratinator

    Ratinator 77.74

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    Thanks gents

    That was especially the confirmation I was after thanks.
    Simon
     
  6. hmangphilly

    hmangphilly The Doctor

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    Is it safe to remove the air cylinder then fire the hammer to see if the air puff is the same ? Will the hammer slam into the end of the chamber and cause any damage ?
    If the puff if air us the same then it's being pushed out by the hammer if it's gone or reduced then some or all has to be leaking past the valve stem.

    Trouble is how to create a seal here without affecting the vital free movement if the valve?
    I think o ring or lip seal would do that . A labyrinth type arrangement would be complicated
     
  7. RobF

    RobF Administrator Staff Member

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    The hammer moves barely a few mm... as much as i'm loathed to contradict Pete, I think you're feeling the air leaking past the valve stem. I've taken mine off and just taped over it. There's not enough pressure to blow the tape off. And any debris finding it's way into that area stands a good chance of being stuck to the tape. Plus it's one less thing to go wrong, or let water etc in...

    I'm guessing the leak % is fairly consistent. As you say, free consistent movement is key
     
  8. Scooby

    Scooby Pete Dutton

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    Hi Rob,

    I didn't say it was only caused by the hammer but when I tested it on mine, without any air in the reg, air can still be felt coming from the dry fire button due to the hammer displacing the air in front of it...don't forget that the hammer moves further than you see when cocking the rifle as it has to knock open the valve.

    I'd suspect that the air moved would be lower on an older rifle as things have worn more but it would be interesting to see if the power goes up slightly if you removed the piece of tape you've used.
     
  9. RobF

    RobF Administrator Staff Member

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    Sorry Pete, my misunderstanding... I'll have a play over the chrono when I get 5.

    (Ever drilled through the hammer all the way through?)
     
  10. Scooby

    Scooby Pete Dutton

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    I've seen a few 10m hammers that have a hole all the way through but assumed this was just reducing the weight as these hammers are also more reduced on the outside than our 12ft/lbs ones. I've seen them with 3mm & 4mm holes inside & when filled with Tungsten TIG electrode the 4mm ones weigh the same as the 12ft/lbs ones.

    At one time I considered grinding 4 longitudinal slots along the length of the hammer to see if it would fly faster but then I couldn't be bothered as the gun worked just fine :D
     
  11. Diabolo

    Diabolo Member

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    Simon posted this to reassure me:eek:

    My previous Dommie was in Lanyman stock, so I never noticed this air movement-so I was a little jittery when I noticed this.

    Thankyou Simon and thankyou to the Walther Guru's on here:)
     
  12. hmangphilly

    hmangphilly The Doctor

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    I wonder if anybody has buttoned a hammer
     
  13. Scooby

    Scooby Pete Dutton

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    The contact areas are very small on the hammer so not sure how beneficial it would be, I have buttoned a pellet probe though but solely to stop it rubbing the blueing from the pellet tray....it helped a lot but after 7years the blueing has still come off :D
     
  14. hmangphilly

    hmangphilly The Doctor

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    pete
    that probe buttoning idea is brilliant.
    it might be the answer to a probe alignment problem ive got.
    the probe is pushed over to the left by the cocking mech and re aligned by the taper of the barrel .
    it scuffs the probe and barrel though and wears out seals

    the hammer buttoning thought was to maybe reduce friction but also , by adding the buttons the diameter could be reduced and leading edge flowed to allow this trapped air to pass by the piston as it travels forward.

    while we're at it does the air behind the hammer / piston create a partial vacuum?

    I appreciate we're talking tiny travel here but just thinking out loud and if simple lubing of the hammer can muck it up ....well you never know...
     
  15. hmangphilly

    hmangphilly The Doctor

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    just done a leakdown test on mine and at 100 psi the leakage past the valve stem is 2-3% according to my guage.
    you can feel and really hear the air leaking out so I'm thinking most of that leaked air is coming down the valve stem.

    now how to control that......
     
  16. Scooby

    Scooby Pete Dutton

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    How did you carry out the test as if your figures scale up you'd be talking approx 35psi getting past the firing valve stem, I can barely feel any air coming from my dryfire switch
     
  17. hmangphilly

    hmangphilly The Doctor

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    pete
    I attached a snap on cylinder leakage tester EEPV309A00 to the muzzle,

    probe closed,
    air cylinder fitted but only filled to 30 bar
    hammer cocked then released against dry fire switch
    join tester to air line
    adjust the leak tester to 100psi

    of course this is a steady 100 psi rather than a sharp blast of 80 odd bar so at this pressure the air has plenty of time to find its way down the stem .
    I'm sure the leakage doesn't scale up to any where near 35psi during firing
    but you could really hear it quite clearly coming out of the safety hole.
    and it does show that there is an appreciable blow by down the stem

    if this was a motor I had rebuilt it would be coming apart again without doubt.
    i'll see if I can do some pics if you cant picture this test....worth a 1000 words and all that
     
  18. Scooby

    Scooby Pete Dutton

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    Don't forget that you still have possible leakage past the probe seal (which rarely seal perfectly) plus the two barrel seals which from the factory are often sliced upon assembly.

    How were you ensuring the firing valve was open?? was it open to the same extent & time as a fired shot

    If you wanted to find out the exact amount of air lost via the valve stem on a particular rifle then you need to have a gauge fitted behind the valve stem & fire an actual shot...not sure how the hammer is going to hit the valve though?

    I think realisically small losses of air are something you just live with as imagine the problems you would create by trying to fully seal the valve stem.
     
  19. sven

    sven Member

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    I agree with Scooby that this is not the right test to quantify the leak past the valve stem and more important that the leak, if any, past the valve stem is something constant and not effecting accuracy. Steyr, Anschutz, Airarms, FX all use an unsealed valve stem so why would you need a sealed one?

    From what I can make of it your test does not measure leak past the valve stem. Because when the hammer is against the dry fire switch the valve is not open. That's the purpose of the dry fire switch: Not opening the valve while releasing the hammer.
    With a closed valve the air should not be coming out of the muzzle. You would have noticed if it did because your cylinder fill would be empty after some time of storage.
    I don't know where your leaking air at the muzzle is coming from but it is unlikely that it is the valve stem.
    The cut away pictures of LG300 breech blocks halfway down on this page http://airgunaccuracy.wordpress.com/walther-lg400-for-field-target/
    might give a clue.

    Would appreciate if you could elaborate on your test.
    Sven
     
  20. hmangphilly

    hmangphilly The Doctor

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    Chaps ,
    I haven't described the test very well .
    Effectively I've attached an air line at 100psi to the muzzle.
    With the probe closed , firing valve is deliberately in the closed position by resting against the dry fire pin .

    Thus the pressurised. Areas are :
    Barrel , probe orifice, transfer port, and the small chamber to the hammer side of the firing valve.
    The valve is closed to eliminate the reg from the test . As all I want to test is the valve stem .

    The barrel seals and probe seal are all fine. No air can be heard escaping and a further test by dusting with talcum powder and firing a pellet confirm this.
    The only escape route for the compressed air is the unsealed valve stem .
    The gauge is academic really and just gives a value to the leak.

    I don't having the firing valve in the open position will make any difference. The amount of lift to the valve upon striking with the hammer, I would say is a tiny amount. Max 0.5 mm I'll try and measure but it is tiny compared to the amount of stem in the drilling of. The action
     

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