SAFETY ALERT! - Tuxing Water Separator Bleed Screw Failure Under Pressure

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Geezerhood

Geezerhood

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Aug 16, 2022
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Southern, Utah, USA

SAFETY ALERT!​

Tuxing Water Separator Bleed Screw Becomes a Projectile Under Pressure​

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I wasn't going to post this but figured I should as the possibility of injury is pretty high.

I had a bleed screw slammed hard into my hand yesterday while opening it near 250 BAR.

Here is what happened
  1. Closed the bleed valve snugly, on the gun side of the water trap / filter in preparation for filling a gun.
  2. Opened the shutoff valve between water trap that was at 250 BAR, and the bleed screw assembly, on the gun side of the water trap, to allow the compressed air in the water trap to equalize in the fill line on the gun side before starting the compressor.
  3. Once the pressure hit the previously unpressurized lines, air could be heard escaping from the bleed screw assembly.
  4. Tightened the knob on the bleed screw slightly to stop the flow with no change.
  5. Closed the shutoff valve between the water trap and the bleed screw.
  6. Started to open the bleed screw to release the pressure in the lines and it shot out of the threaded insert and slammed into the palm of my hand with significant force and pain with a very loud BANG.! The pressure was for sure less than the starting pressure of 250 BAR since air had been escaping, but I did not make a note of it.
  7. The volume of air would have only been what was in the whips and a small water filter which had the bleed screw assembly in it.
    (Fortunately, due to the fairly large frontal surface of the knob on the bleed screw, there was no serious damage to my hand. It felt like what trying to catch a golf ball sized rock that someone had thrown pretty hard might be like.
  8. At least one expletive was heard in the room. I am assuming spoken by me.
  9. After removal and inspection of the assembly I could tell that the threads on the screw body had been sheared off enough to allow the screw assembly to be blown free of the threaded insert it was in.
  10. Replaced it with a new, complete bleed screw assembly I had on hand.
  11. Back to normal function now. (But it is not safe in my opinion!!)
I thought that the screw itself was steel, but on inspection it turned out to be silver plated brass. The threaded insert from the assembly is stainless steel as far as I can tell, using a magnet and hitting a corner with a file to reveal the metal underneath. It is working as it should now, but the replacement bleed screw on the new assembly is also made of brass and could also fail over time like the original one did. So, I am going to replace it as well as all the other same type of brass bleed screws with steel parts ASAP. It failed after almost daily use for 5 months.

Some other observations

  • The area on the bleed screw where the tops of the threads were stripped off is showing brass underneath.
  • On very close inspection, the threads in the insert that was in place when the bleed screw failed look perfect. The steel is very hard as well, compared to some other stainless parts I have. I don't think the problem was the insert.
  • The "fit" of a new bleed screw of the same type with threaded insert is very loose both front to back and side to side rattling on all three assemblies I have of this type - which concerns me. I never noticed how sloppy the fit was until now.
  • I can press the stripped screw into all three of the threaded inserts I have, almost 1/4" without turning it. The replacement "good" screw will not enter the fitting at all by pressing it in.
  • The visible thread damage on the screw is 0.30" long which is pretty much the amount of threads that are inside the insert when the valve is closed.
  • While waiting for replacements, I am going to see if I can find a tight fitting metric grade 8 steel screw to use instead of these brass screws.
I will post photos later.
 
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The bottom bleed screw is the one with the stripped threads. The top one has only been opened and closed a few times on my water trap because I keep it under pressure most of the time. Both came on products sold by Tuxing.

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I am thinking about replacing all the bleed valves of this type that I have, with what seems to me to be a better design. I have one like this one on my SCBA fill station and it has been problem free for quite a while.

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I got the replacement bleed valves that were ordered on eBay. From the day the order was placed to having it in my hands was 11 days - coming from from China. They are very well made with a much better design than the simple screw with some of the threads ground off to let the air out. The seal is more positive than the Tuxing style assembly and takes less movement to get a large volume of air moving through if needed quickly for some reason. I will post photos of the inside later.

I got two of both thread sizes, which ended up being a good thing since the small Tuxing filter with the bleed screw on it ended up being 1/8" NPT thread which surprised me, and the two on the big gold filter were M10. I used teflon tape on the 1/8 NPT as well as the Teflon washer they sent with it and it is leak free on the first try.

I checked the other two Tuxing bleed screws on my large two cylinder moisture / oil filter and drier. They both now show signs of the threads giving away. The one I use the most of the two was in the worst shape. I replaced all three of them with these new ones. My fingers are now more at ease with this bleeder assembly. If you are constantly opening and closing the bleed screw on your Tuxing filters, I would suggest that you inspect them for thread damage to avoid having one launched under pressure.

I compared the Tuxing bleeders to the ones on my Yong Heng compressor. The Yong Heng is a much safer design in my view with significantly longer thread engagement and no weakening flats ground on the screw. The screw is steel, the fitting brass They have an exit hole at 90 degrees like these replacement ones. I will post photos of the Yong Heng parts later. No hint of thread damage on the Yong Heng screws with 25 hours of use on it, bleeding multiple times a day. I have never seen a thread about the bleed screw failure on the Yong Hengs. Have any of you experienced a failure?

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dorcula said:
Well, damn. Thanks for the heads up. My Tuxing 032 compressor has these loosely fitting brass bleed screws. Not going to use it until I replace them.
Click to expand...

Did they show any signs of wear on the threads? Look with a magnifier and compare the threaded area above where it goes into the fitting to what is inside the fitting. It is possible mine was made of softer material, but who knows. I didn't use mine after that blast in the hand.

Those replacements I got off eBay are still working perfectly. Just make sure you get the right thread size. Most likely M10 but good to verify.
 
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dorcula said:
My screws look good. They just feel very loose in the fitting. What your pictures show is not wear: they show the peaks of the threads stripped by force and I would guess this was exactly because the diameter of the treaded hole was larger than needed for proper thread engagement.
Click to expand...

Yea, wear probably wasn't the best choice of words to use. In addition to poor thread to insert fitment, the amount of contact from the insert is miniscule compared to the parts on my Yong Heng.
 
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dorcula said:
These stainless bleed valves work great, thanks again for the tip!
Click to expand...

You are welcome! I installed 2 of them a while ago and they are working perfectly for me. Much easier to control the flow with less rotation of the knob than what came with it and a safer design in my opinion.

Note: They are not stainless Steel. Pretty sure they are chrome plated brass, rated in the ebay listing at 5000 PSI max operating pressure.
 
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Updated with a photo of the setup with the replacement bleed valve installed.

I don't recall the specs on the fittings. They were items I had in my parts box. The seals on the shutoff valve was accomplished with Dowty Washers. I replaced the set screw that held the knob on the shutoff valve with a hex key screw to make it easier to turn the knob. As the pressure goes up, the resistance to turning also increases. At 4500 PSI it is pretty hard to move with just my fingers.

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