I apologize in advance for the length of this post, but if you're suffering from this issue you probably want as much info as possible.
Do you have a Yong Heng compressor? Do you keep blowing burst discs for no apparent reason? If so, read on...
I bought a Yong Heng compressor a few months ago and was able to fill my two big tanks just once before I started encountering issues with the compressor. The second time I tried to use my compressor I got up to about 3300 PSI and then it just held at that pressure, even after several minutes. I turned off the compressor and could immediately hear air leaking from the compressor. I got out a spray bottle of soapy water and found out immediately that the leak was coming from where the fill hose attached directly to the high-pressure output manifold port.
I tried to just tighten the connection to fix the issue, but the connection was already relatively tight and further tightening didn't help at all.
It is at this point I entered what I now call "Yong Heng Compressor Hell". By that I mean I realized at this point I did not know much about the compressor's internals, and the crappy Chinglish manual did not help whatsoever. Google to the rescue, right? Wrong. Lots of folks posting "facts" which just were not true. For example, what threads were used? Someone said BSPP. Someone else said NPT. Someone else said NF (non-tapered NPT). Someone else said Metric, M10. Those threads are indeed M10. But there are at least 3 different M10 threads. The M10 threads the Yong Heng uses are M10x.1, not M10x1.25 nor M10x1.5.
I decided I'd try to find a M10x1.0 to 1/8" FPT adapter. I found one, and tried it, and it worked twice before it started leaking and I got rid of it as it was meant for a fuel pressure sending unit and was made from copper, so you can bet its working pressure was just a few hundred PSI. Instead, I decided I would tap the aluminum block's threads with 1/4" MPT, then use a 1/4" MPT to 1/8" FPT adapter. That would also allow me to use my NPT Foster fittings. This worked, and I was able to put a Foster 12MPS plug fitting directly on the aluminum block, which in turn allowed me to connect a PCP hose with a Foster socket (Foster 12FSS) to it. This was great and I figured I was done with the compressor leaking.
Long, long story short: just about everything that connects to that aluminum manifold began leaking, including the pressure gauge and the burst disk.
I ended up replacing the entire aluminum manifold with a new one from AliExpress.
I also found out a lot about the different thread types during this process. For example, only NPT threads seal via the threads themselves. The BSPP and Metric connectors seal via the connector's shoulder or head with the help of a gasket or bonded washers, aka Dowty Seals. But in addition to the Dowty seals, there are also small rubber O-rings and small plastic washers the same size as the O-rings. I was not sure when I should use a Dowty seal and/or rubber O-ring and/or plastic washer. The manual was of no help.
I have come to find that the Dowty seals are used for BSPP and Metric connections.
I have also come to find out that the small white plastic seals are called Polyoxymethelene/Polyacetal seals, aka POM seals.
I have also come to find out the relationship between the rubber O-rings and the POM seals. I mean, under what conditions would one use rubber O-rings and under what conditions would one use POM seals? Are they used together? Always? The answer is that, for a typical application--which the Yong Heng compressor is not--both would indeed be used. The purpose of the POM seals is to act as a backup ring that prevents the much softer O-ring from entering the gap it is supposed to seal. When high pressure is applied to the O-ring, its soft rubber material may be forced into the gap, causing the O-ring to extrude. The POM seal prevents the O-ring material from flowing into the gap, preventing premature failure. Now, that is true in general but not for the Yong Heng compressor. The Yong Heng compressor typically only uses POM seals and not rubber O-rings. Here is how the POM seals are used on Yong Heng:
Here we can see that the Pressure Gauge, High Pressure Fill Hose port and Moisture Drain Screw all use POM seals but do not use rubber O-rings, too. There are a few points to clarify here. First, the port on the manifold that the fill hose connects to is not labeled in the diagram. The port is directly above the Moisture Drain Screw (which is alternatively referred to in the manual as the Drain Cock). Second, the port on the manifold labeled “Exhaust Airhose Connect” is not correct—if anything that name should refer to the Fill Hose connection which is not labeled. The port that is labeled “Exhaust Airhose Connect” would be better called “High Pressure Manifold Input from 2nd Stage Discharge Connect”. Whatever this port on the Manifold is called, it uses a Compression Fitting in addition to a bonded sealing gasket (Dowty seal).
One may be tempted to conclude that O-rings are not used in conjunction with POM seals on the Yong Heng compressor, but this probably isn’t true. For example, should you order additional M10 Quick Disconnect Sockets from China, they will arrive with both a POM seal *and* multiple rubber O-rings:
So, perhaps, the Quick Disconnect adapters connect to Air Hoses via both rubber O-rings and POM seals. Not sure! I am sure that the rubber O-rings are not used on the high-pressure manifold for the Pressure Gauge port, High Pressure Fill Hose port and Moisture Drain Screw port.
Now, some observations about the Explosion Prevention valve and port on the Manifold. First, note that it does not use any type of seal or gasket—not a POM seal, not a rubber O-ring and not a bonded washer (Dowty seal). So, what prevents air from leaking from where the Explosion Proof valve connects to the Manifold? I have no idea!
For the record, the Explosion Proof valve uses M10x1.0 threads just like all the other ports on the Manifold. While consistent with the other ports on the Manifold, the M10x1.0 threads make it practically impossible to replace the Explosion Proof valve with a 3rd party valve. I was not able to find an Explosion Proof valve with M10 threads. I found several 3rd party Explosion Proof valves (in both 5k PSI and 7.5k PSI burst values), but every single one I found comes with “standard 3/8" threads”. These are not NPT threads nor Metric threads as they are not tapered. I really wish folks would use more explicit, accurate definitions. I am not 100% sure but strongly suspect that “standard 3/8” threads” are more accurately defined as 3/8”-24 NF threads. What is a NF thread? NF stands for National Fine (as opposed to National Course). The National designation is from the old United States Standard which was replaced by the American National Standard for Unified Threads in 1949. Whatever NF is it is it will not screw into a M10x1.0 opening. And there does not appear to be a NF to Metric coupler (at least that I could find).
Backing up a bit, one might ask the question “Why would you want to replace the burst disk/valve in the first place?”
In my case, I was looking to replace the Burst Valve because the Burst Disc kept blowing on me prematurely and I thought the valve itself and/or burst discs were defective somehow. I was not able to pressurize to above 1,500 PSI before the burst disc would blow. I researched this issue to see if I was the only one experiencing it and I was not. In fact, there were a few posts related to Burst Discs popping prematurely on this forum. One shooter was looking to replace the stock Burst Disc like I was. Another shooter suggested using calibers to find the variance in thickness of the Burst Discs and using the thickest one. And yet another shooter suggested just using two Burst Discs at once. As none of these options sounded acceptable to me, I almost gave up on my Yong Heng compressor before I found a clue that led me to the root cause of my Burst Discs blowing prematurely and the solution to the issue.
My clue as to the root cause came when I blew my last Burst Disc. When it blew, I fully depressurized the compressor by loosening the Moisture Drain Screw. The air whooshed out of compressor and the compressor’s pressure gauge dropped to 0 as one would expect. HOWEVER, I noticed that the gauge on my fill tank still showed 1,000 PSI. It should have dropped to 0, too.
My first thought was that I had forgotten to remove one of the one-way valves that came standard in some of the Quick Disconnect fittings I used. I normally use “name brand” “straight thru” fittings, namely Foster/ZSi-Foster/Breco fittings (Breco is a company Foster purchased recently which added a SS303 socket with 1/8” MPT threads to Foster’s lineup which was previously missing). The straight thru fittings do not have a directional flow valve inside of them, but the cheaper Quick Disconnect fittings I had recently purchased did:
I normally take the flow control valve out of the fitting before use:
The thought occurred to me: What if I forgot to take the flow control valve out? If that were the case it would explain why my Burst Discs kept popping prematurely and it would explain why my fill tank remained semi-pressurized even though the compressor itself was completely depressurized!
I proceeded to check each Quick Disconnect fitting I had along the entire air output path. I was a little surprised to find that I had not forgotten to remove all the flow control valves—all had been removed.
But *something* must explain why my fill tank remained pressurized even though the compressor was completely depressurized. The root cause finally came to me—something must be preventing my fill tank from depressurizing, even if it wasn’t a wrongly positioned flow control valve inside one of the Quick Disconnect fittings. I checked my two air drying filters first. They were both clean. Then I checked my three hoses and, sure enough, the last one I checked I could not blow air through with my mouth! One of the cheap-ass High Pressure Hoses that came with the compressor was clogged! I got out a small paperclip and inserted it into one end of the cable. I was able to insert it all the way to where the fitting met the cable. I then checked the other end. I was only able to insert the paperclip about ¼” into the fitting. Something was there! I tried using the paperclip to pull out whatever was blocking the hose but could not get anything to come out. I then got the bright idea (being facetious here) to use high pressure air to “blow out” whatever foreign material was stuck in the hose. I first tried with my Great White tank but because of the Slow Flo valve on the Great White it did not work—I needed full pressure immediately. I switched tanks to my SCUBA tank and tried again. I held the hose firmly in one hand and turned the valve open on the fill tank with my other hand. I immediately heard a loud “pop” as whatever was in the hose was violently blown out of it. In the process the hose came out of my hand and almost wacked me! This was obviously a stupid thing to do. A $10 Chinese HPA hose is not worth severe injury! DO NOT DO THIS!
All that said I tried refilling my tanks again now that there was no blockage anywhere between the compressor and the fill tank. It worked beautifully! Problem solved!
Bottom line: If you keep blowing Burst Discs unexpectedly check for blockage in your filters and hoses. Do not double-up on Burst Discs!
Hope this helps somebody!!
Best,
Sean.
P.S. – I do not know what foreign material was blocking the hose, but I suspect it was one of two things. Either I used a O-ring and a POM seal but in the wrong order (O-ring then POM seal then Quick Disconnect fitting when it should have been POM seal then O-ring then Quick Disconnect fitting) when attaching the Quick Disconnect fitting to one of the high pressure hoses and the O-ring was pushed inside the hose OR it was a piece of metal from when I drilled and tapped the aluminum block to accept NPT threaded fittings. If you do end up tapping the aluminum block for different threads make sure to take the manifold block off from the compressor completely before drilling and make sure there are no shavings in any of the crevices when finished.
P.S.S -- Be careful tightening fittings/gauges/burst discs/etc to the aluminum manifold (aka gauge base). I actually broke off the manifold from the Motor Bracket when torquing down the fill hose Quick Disconnect to the manifold. The manifold is not under a lot of pressure/stress once everything is in place so I was able to JB weld the manifold back into place but the metal is cheap and breaks easily! Wish the manual gave torque specs...
Do you have a Yong Heng compressor? Do you keep blowing burst discs for no apparent reason? If so, read on...
I bought a Yong Heng compressor a few months ago and was able to fill my two big tanks just once before I started encountering issues with the compressor. The second time I tried to use my compressor I got up to about 3300 PSI and then it just held at that pressure, even after several minutes. I turned off the compressor and could immediately hear air leaking from the compressor. I got out a spray bottle of soapy water and found out immediately that the leak was coming from where the fill hose attached directly to the high-pressure output manifold port.
I tried to just tighten the connection to fix the issue, but the connection was already relatively tight and further tightening didn't help at all.
It is at this point I entered what I now call "Yong Heng Compressor Hell". By that I mean I realized at this point I did not know much about the compressor's internals, and the crappy Chinglish manual did not help whatsoever. Google to the rescue, right? Wrong. Lots of folks posting "facts" which just were not true. For example, what threads were used? Someone said BSPP. Someone else said NPT. Someone else said NF (non-tapered NPT). Someone else said Metric, M10. Those threads are indeed M10. But there are at least 3 different M10 threads. The M10 threads the Yong Heng uses are M10x.1, not M10x1.25 nor M10x1.5.
I decided I'd try to find a M10x1.0 to 1/8" FPT adapter. I found one, and tried it, and it worked twice before it started leaking and I got rid of it as it was meant for a fuel pressure sending unit and was made from copper, so you can bet its working pressure was just a few hundred PSI. Instead, I decided I would tap the aluminum block's threads with 1/4" MPT, then use a 1/4" MPT to 1/8" FPT adapter. That would also allow me to use my NPT Foster fittings. This worked, and I was able to put a Foster 12MPS plug fitting directly on the aluminum block, which in turn allowed me to connect a PCP hose with a Foster socket (Foster 12FSS) to it. This was great and I figured I was done with the compressor leaking.
Long, long story short: just about everything that connects to that aluminum manifold began leaking, including the pressure gauge and the burst disk.
I ended up replacing the entire aluminum manifold with a new one from AliExpress.
I also found out a lot about the different thread types during this process. For example, only NPT threads seal via the threads themselves. The BSPP and Metric connectors seal via the connector's shoulder or head with the help of a gasket or bonded washers, aka Dowty Seals. But in addition to the Dowty seals, there are also small rubber O-rings and small plastic washers the same size as the O-rings. I was not sure when I should use a Dowty seal and/or rubber O-ring and/or plastic washer. The manual was of no help.
I have come to find that the Dowty seals are used for BSPP and Metric connections.
I have also come to find out that the small white plastic seals are called Polyoxymethelene/Polyacetal seals, aka POM seals.
I have also come to find out the relationship between the rubber O-rings and the POM seals. I mean, under what conditions would one use rubber O-rings and under what conditions would one use POM seals? Are they used together? Always? The answer is that, for a typical application--which the Yong Heng compressor is not--both would indeed be used. The purpose of the POM seals is to act as a backup ring that prevents the much softer O-ring from entering the gap it is supposed to seal. When high pressure is applied to the O-ring, its soft rubber material may be forced into the gap, causing the O-ring to extrude. The POM seal prevents the O-ring material from flowing into the gap, preventing premature failure. Now, that is true in general but not for the Yong Heng compressor. The Yong Heng compressor typically only uses POM seals and not rubber O-rings. Here is how the POM seals are used on Yong Heng:
Here we can see that the Pressure Gauge, High Pressure Fill Hose port and Moisture Drain Screw all use POM seals but do not use rubber O-rings, too. There are a few points to clarify here. First, the port on the manifold that the fill hose connects to is not labeled in the diagram. The port is directly above the Moisture Drain Screw (which is alternatively referred to in the manual as the Drain Cock). Second, the port on the manifold labeled “Exhaust Airhose Connect” is not correct—if anything that name should refer to the Fill Hose connection which is not labeled. The port that is labeled “Exhaust Airhose Connect” would be better called “High Pressure Manifold Input from 2nd Stage Discharge Connect”. Whatever this port on the Manifold is called, it uses a Compression Fitting in addition to a bonded sealing gasket (Dowty seal).
One may be tempted to conclude that O-rings are not used in conjunction with POM seals on the Yong Heng compressor, but this probably isn’t true. For example, should you order additional M10 Quick Disconnect Sockets from China, they will arrive with both a POM seal *and* multiple rubber O-rings:
So, perhaps, the Quick Disconnect adapters connect to Air Hoses via both rubber O-rings and POM seals. Not sure! I am sure that the rubber O-rings are not used on the high-pressure manifold for the Pressure Gauge port, High Pressure Fill Hose port and Moisture Drain Screw port.
Now, some observations about the Explosion Prevention valve and port on the Manifold. First, note that it does not use any type of seal or gasket—not a POM seal, not a rubber O-ring and not a bonded washer (Dowty seal). So, what prevents air from leaking from where the Explosion Proof valve connects to the Manifold? I have no idea!
For the record, the Explosion Proof valve uses M10x1.0 threads just like all the other ports on the Manifold. While consistent with the other ports on the Manifold, the M10x1.0 threads make it practically impossible to replace the Explosion Proof valve with a 3rd party valve. I was not able to find an Explosion Proof valve with M10 threads. I found several 3rd party Explosion Proof valves (in both 5k PSI and 7.5k PSI burst values), but every single one I found comes with “standard 3/8" threads”. These are not NPT threads nor Metric threads as they are not tapered. I really wish folks would use more explicit, accurate definitions. I am not 100% sure but strongly suspect that “standard 3/8” threads” are more accurately defined as 3/8”-24 NF threads. What is a NF thread? NF stands for National Fine (as opposed to National Course). The National designation is from the old United States Standard which was replaced by the American National Standard for Unified Threads in 1949. Whatever NF is it is it will not screw into a M10x1.0 opening. And there does not appear to be a NF to Metric coupler (at least that I could find).
Backing up a bit, one might ask the question “Why would you want to replace the burst disk/valve in the first place?”
In my case, I was looking to replace the Burst Valve because the Burst Disc kept blowing on me prematurely and I thought the valve itself and/or burst discs were defective somehow. I was not able to pressurize to above 1,500 PSI before the burst disc would blow. I researched this issue to see if I was the only one experiencing it and I was not. In fact, there were a few posts related to Burst Discs popping prematurely on this forum. One shooter was looking to replace the stock Burst Disc like I was. Another shooter suggested using calibers to find the variance in thickness of the Burst Discs and using the thickest one. And yet another shooter suggested just using two Burst Discs at once. As none of these options sounded acceptable to me, I almost gave up on my Yong Heng compressor before I found a clue that led me to the root cause of my Burst Discs blowing prematurely and the solution to the issue.
My clue as to the root cause came when I blew my last Burst Disc. When it blew, I fully depressurized the compressor by loosening the Moisture Drain Screw. The air whooshed out of compressor and the compressor’s pressure gauge dropped to 0 as one would expect. HOWEVER, I noticed that the gauge on my fill tank still showed 1,000 PSI. It should have dropped to 0, too.
My first thought was that I had forgotten to remove one of the one-way valves that came standard in some of the Quick Disconnect fittings I used. I normally use “name brand” “straight thru” fittings, namely Foster/ZSi-Foster/Breco fittings (Breco is a company Foster purchased recently which added a SS303 socket with 1/8” MPT threads to Foster’s lineup which was previously missing). The straight thru fittings do not have a directional flow valve inside of them, but the cheaper Quick Disconnect fittings I had recently purchased did:
I normally take the flow control valve out of the fitting before use:
The thought occurred to me: What if I forgot to take the flow control valve out? If that were the case it would explain why my Burst Discs kept popping prematurely and it would explain why my fill tank remained semi-pressurized even though the compressor itself was completely depressurized!
I proceeded to check each Quick Disconnect fitting I had along the entire air output path. I was a little surprised to find that I had not forgotten to remove all the flow control valves—all had been removed.
But *something* must explain why my fill tank remained pressurized even though the compressor was completely depressurized. The root cause finally came to me—something must be preventing my fill tank from depressurizing, even if it wasn’t a wrongly positioned flow control valve inside one of the Quick Disconnect fittings. I checked my two air drying filters first. They were both clean. Then I checked my three hoses and, sure enough, the last one I checked I could not blow air through with my mouth! One of the cheap-ass High Pressure Hoses that came with the compressor was clogged! I got out a small paperclip and inserted it into one end of the cable. I was able to insert it all the way to where the fitting met the cable. I then checked the other end. I was only able to insert the paperclip about ¼” into the fitting. Something was there! I tried using the paperclip to pull out whatever was blocking the hose but could not get anything to come out. I then got the bright idea (being facetious here) to use high pressure air to “blow out” whatever foreign material was stuck in the hose. I first tried with my Great White tank but because of the Slow Flo valve on the Great White it did not work—I needed full pressure immediately. I switched tanks to my SCUBA tank and tried again. I held the hose firmly in one hand and turned the valve open on the fill tank with my other hand. I immediately heard a loud “pop” as whatever was in the hose was violently blown out of it. In the process the hose came out of my hand and almost wacked me! This was obviously a stupid thing to do. A $10 Chinese HPA hose is not worth severe injury! DO NOT DO THIS!
All that said I tried refilling my tanks again now that there was no blockage anywhere between the compressor and the fill tank. It worked beautifully! Problem solved!
Bottom line: If you keep blowing Burst Discs unexpectedly check for blockage in your filters and hoses. Do not double-up on Burst Discs!
Hope this helps somebody!!
Best,
Sean.
P.S. – I do not know what foreign material was blocking the hose, but I suspect it was one of two things. Either I used a O-ring and a POM seal but in the wrong order (O-ring then POM seal then Quick Disconnect fitting when it should have been POM seal then O-ring then Quick Disconnect fitting) when attaching the Quick Disconnect fitting to one of the high pressure hoses and the O-ring was pushed inside the hose OR it was a piece of metal from when I drilled and tapped the aluminum block to accept NPT threaded fittings. If you do end up tapping the aluminum block for different threads make sure to take the manifold block off from the compressor completely before drilling and make sure there are no shavings in any of the crevices when finished.
P.S.S -- Be careful tightening fittings/gauges/burst discs/etc to the aluminum manifold (aka gauge base). I actually broke off the manifold from the Motor Bracket when torquing down the fill hose Quick Disconnect to the manifold. The manifold is not under a lot of pressure/stress once everything is in place so I was able to JB weld the manifold back into place but the metal is cheap and breaks easily! Wish the manual gave torque specs...
