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DAR Dar Gen III leaking from main valve body.

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Phil.Probe

Phil.Probe

Member
Feb 20, 2022
125
110
Utah, United States
Finally got around to trying to fixing my DAR gen III today. I replaced the reg with a Huma (original one wasn't working), but now I've got a slow leak from the main valve body. Air is coming from what I'm guessing is the transfer port (big hole between the two o-rings). It seems like the valve isn't sealing 100%.

I couldn't see a way to disassemble the main valve body once I unscrewed it from the plenum. Do I just order a new MVB from DAR, or does anyone have any suggestions? I also replaced all the o-rings, but non looked damaged or worn.

I'm new to fixing this stuff so I might have my terminology wrong... there's no schematic for the DAR gen III, so I'm just going off this PDF at the end of the manual for the JTS



MVB.jpg
 
A slow leak there usually indicates the poppet isn't sealing completely. You can use a light abrasive slurry (ballpark of 600 - 1000 grit) to lap the surfaces together. Color the mating surfaces with a black Sharpie or dye, then spin the surfaces together for a short time, and wipe it clean and view the surfaces with the aid of magnification. The low spot(s) will still have the marker. Continue lapping until all the marking is removed and you have a smooth, continuous ring of contact.

"Usually" in this case because the DAR valve has a brass insert that can potentially leak in the same manner. If you didn't already replace its O-rings as part of the aforementioned repair, check it. It is secured to the valve body with the grub screw shown in your photo.
 
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