Tuning O-ring failure, Kral Puncher Monarch

[Murderkitty]

I have new purchased Kral Puncher Monarch from Krale.shop and have been having issues with pressure. This is my first PCP airgun, and the first time I've tried to fill it since getting it. 

First, it would leak through the barrel when I tried to charge it. I was told this might be an obstruction in the valve, so I (with great difficulty, thanks to ample Loctite) took apart the tank and checked it out. Putting it back together I found no improvement, but was eventually able to get it to hold pressure by spamming the handpump really, really hard... until I got to 100BAR. 

At 100 BAR, a new leak emerged. This time it's from the probe, and I cannot get the gun over 100BAR. The probe's second (further from pump) o-ring had been chomped apart, like Homer Simpson bit a donut. I gently coaxed the bit that had been bitten out from the port, replaced the o-ring, and began filling again... only for the leak to come back, again around 100 BAR. I took the probe out, and sure enough Homer had struck again. 

A bit of experimentation showed that the rings got damaged on insertion, but didn't get "bitten" until just under 100 BAR. I've run out of o-rings the gun came with and started using standard #5 sized orings instead. They failed a little less spectacularly, with only a little nibble taken out of them, but the effect was the same. 100BAR is as far as she'll go. 

TL;DR: My airgun destroys orings on the probe. What could cause this? How can I resolve it? 

 

[pnwairgunner]

Without seeing exactly what’s happening, it kind of sounds like the poppet is leaking AND it sounds like there’s a burr in the breech or maybe at the transfer port hole in the barrel that is cutting the probe o ring.

 

[Murderkitty]

Poppet? Is that the valve out of the tank on the barrel side? That leak resolved when I got enough air into the tank. The tank will hold air without loss... but only up to ~100BAR. 


A burr had occurred to me, but I can't find it by visual inspection. What would I do to get rid of it if there was one?

 

[FuzzyGrub]

If you haven’t, use silicone grease on the fill probe, and when you are inserting it, turn it back and forth.

if burr, rolled up sandpaper. Clean it out well with que tip and alcohol. Regrease probe. 

 

[pnwairgunner]

Yes what fuzzygrub said. I would add that it is best to take the barrel off to check for burrs and use a dental pick to feel for any machined edges that the dental pick “sticks to” around the transfer port hole and breech and muzzle while you are at it. But something to keep in mind is that you may tear the outer-barrel o rings when re-inserting the barrel into the breech block, so you’ll want to have plenty of spare o rings on hand before you even start, as well as pure silicone grease to lubricate them before inserting them. 
If you aren’t proficient with working on PCP’s I would strongly encourage you to find a reputable person on here to work on it for you, or better yet send it back for a replacement. It can be very dangerous to work on, and an inexperienced person could cause some pretty expensive damage to the airgun in damaged/lost parts. It can’t be stressed enough that improper work on an airgun could create a very dangerous or lethal situation for yourself or folks nearby. 

 

[100acres]

I would just return the gun for a replacement since it is new and you are having these type of issues.

 

[darylm]

You should pull the side lever back when filling.

 

[Murderkitty]

A few rounds of sanding and charging gave no improvement. The o-rings are definitely being nommed on the valve side of the inlet. As best I can tell they get damaged on insertion, then blow out around 50-100BAR, meaning the gun can't get above the 120BAR or so it has in it now. If there is a burr its around that valve port, but I can't see or feel it with anything. 

I'm going to buy some 9x2mm o-rings, since I'm using imperial ones on a metric probe now. Of course, the probe ate all of the metric o-rings that came with it too so I doubt it will be very picky. I am also considering a new probe, but there's only so much to blame on that end. 


I would consider a return, but I've bumped and scraped up a lot on the gun already through attempted repairs, and a return would be dubious. There might have been nothing wrong to begin with, other than needing to spam in enough air to make the valve closed. A failed return would be a huge waste of time and money, so I want to exhaust repair first. Plus, the company is in Turkey and has a help line that is open the exact same 8 hours each day as I have to sleep during for a workday. 

 

[pnwairgunner]

A few rounds of sanding and charging gave no improvement. The o-rings are definitely being nommed on the valve side of the inlet. As best I can tell they get damaged on insertion, then blow out around 50-100BAR, meaning the gun can't get above the 120BAR or so it has in it now. If there is a burr its around that valve port, but I can't see or feel it with anything. 

I'm going to buy some 9x2mm o-rings, since I'm using imperial ones on a metric probe now. Of course, the probe ate all of the metric o-rings that came with it too so I doubt it will be very picky. I am also considering a new probe, but there's only so much to blame on that end. 


I would consider a return, but I've bumped and scraped up a lot on the gun already through attempted repairs, and a return would be dubious. There might have been nothing wrong to begin with, other than needing to spam in enough air to make the valve closed. A failed return would be a huge waste of time and money, so I want to exhaust repair first. Plus, the company is in Turkey and has a help line that is open the exact same 8 hours each day as I have to sleep during for a workday.

As you’ve said, you’ve bumped and scraped up a lot already. You have (or had) a really nice, really pretty air rifle, I suggest sending a message to Thammer (Troy Hammer) on here or anyone else of your choosing to ask about having a look at your air rifle. Troy has a lot of experience with Kral rifles. Let someone fix it for you and minimize the damage. What state do you live in? 
**edit I see it says you are in Alabama. Can you post some pics of the probe and the breech? 

 

[FuzzyGrub]

I only have a few guns that use a fill probe vs a foster. No direct experience with the Krall fill probe. On one of my guns, the probe O-rings had to be the exact size and durometer. It wasn’t a leak, but the probe would pop out if you didn’t hold it in.


It is common to tear them up with use and why they should be lubed. The size and type of cut in the O-ring should help id it. Small chucks probably burr. Sliced half moons is probably a sharp edge.

 

[Murderkitty]

https://ibb.co/Z8BJx6v
https://ibb.co/tMXKR36

https://ibb.co/J37m23Q

https://ibb.co/DRNw8xQ


A few pics of the port, probe, and size comparison of old and new o-rings. I'm thinking new metric o-rings will be a start, because while my black ones fail less completely than the originals (which were softer) it's certainly not helping avoid damage that it's slightly oversize. Maybe the rings I've ordered will resolve the issue. I will have to see how that goes before pushing much further. 

 

[Tru]

I had something similar when I was filling mine. I ordered a fill probe with quick connect. Then lubed the o rings and filled in the fill port. It stopped the issue for me.

 

[thammer]

The Monarch is just a Kral knight with the valve and tube from a Kral mega and a stock adjusted to fit the tube instead of a bottle. There's sometimes a sharp edge that cuts the first oring going in plus a hand pump doesn't keep constant pressure high enough to seal the orings. It's a little tedious but not a hard fix. If you just need that taken care of you can pull the tube with valve attached and send that to me or I can do a full tune and get you a little more performance as well. 

Troy

 

[rc4fun]

https://ibb.co/Z8BJx6v
https://ibb.co/tMXKR36

https://ibb.co/J37m23Q

https://ibb.co/DRNw8xQ


A few pics of the port, probe, and size comparison of old and new o-rings.

That fill probe looks a bit chewed you could try to polish it some with a Dremel or order an aftermarket one that is built better. Or just send it to Troy.

 

[Murderkitty]

https://ibb.co/Z8BJx6v
https://ibb.co/tMXKR36

https://ibb.co/J37m23Q

https://ibb.co/DRNw8xQ


A few pics of the port, probe, and size comparison of old and new o-rings.

That fill probe looks a bit chewed you could try to polish it some with a Dremel or order an aftermarket one that is built better. Or just send it to Troy.

What would be a good bet for aftermarket? I have tried sanding it, breaking the corners around the oring channels, and re inserting it. The scratches and dings there come back fairly quickly. Maybe it's the size of o-ring making it go in crooked though. 

Tomorrow I should be getting better sized o-rings. I shot what I was able to get into the tank on Sunday, and the rifle works fine otherwise, but I was unable to get it back up at all. 


I'm a bit hesitant to throw money into work on the gun, but I'm happy with how it shot when it shot, so I'll have to give it some thought. My experience with firearms has left me a little out of my depth when it comes to valves and rubber o-rings. 

EDIT: New o-rings did not help. It was difficult to push the probe in, and doing so shredded the o-rings. They may be too hard. Might try a new probe. 

 

[Murderkitty]

Update: 

New fill probe was a success! Kicking myself for not trying it right off the bat when I ordered the o-rings. 

It seems like all is working well with the rifle. Filled it, shot it, and refilled it again this afternoon. Thinking I'll take it to a range tomorrow to get a little more in depth with it. 

Thank you to all who gave advice! 

 

[Fatmike]

Has it been to long to return it? Troy Hammer might be able to help you out if you cant get a replacement.