I spent the weekend getting some pneumatics components together for a couple of small projects that has been back-burnered for a year. In the process, I was reminded of several things that bug me about working with compressed air piping and pneumatic components.
I’ve had frustrating time these past 2 days, so maybe this will come across as too grumpy. Overall, pneumatic fittings and systems are relatively easy to rig together. But when something goes wrong, such as a super-slow but persistent air leak (see #1), everything kind of ties together to bug the heck out of me.
I’ll probably shrug it off and live with the minute air leak for now, until it bugs me again (tomorrow?). But for now, every aspect of the compressed air system is getting on my nerves.
Some of this applies to air compressors from a tool context, some of it applies to air lines in an industrial and automation context. The couple of small projects I have in the works mainly involve the use of pneumatic actuators, and one involves a blower for a small CNC build. But some of these could be universal annoyances.
1. Air Leaks
20 hours into leak testing of my closed-loop system, and the air pressure is down from 60 PSI to around 40 PSI. There’s not a lot of volume in the system – the tank is only about 13.5 cubic inches, and then whatever’s in the air lines. But still, a leak is a leak.
I believe the leak has something to do with my air filter and regulator. But I removed the fittings, cleaned the threads, added new fittings, re-cut the air lines, and there’s no improvement.
The air filter and regulator connect together via a spacer device, but that seems to be a solid seal. If the leak is in the interface between filter and regulator, or in either component, there’s nothing I can do short of swapping parts back and forth to try to isolate the culprit.
I plan to do some quick leak detecting, but it’s not going to be easy.
2. Teflon Tape
I have some good teflon tape that I bought about a year ago with many of the parts for this project. Can’t find it anywhere. Am I the only one who always loses teflon tape? Good thing I have a cheap roll in my top toolbox drawer for times like this.
How many times to wrap a thread? 2 times? 3? Certainly not 1, and certainly not 5, at least for the 1/8 NPT fittings I’m using. Too little, and the tape won’t be effective. Too much, and it’ll bunch up. Use the right amount, and it might still bunch up.
I found myself in need of some 1/4″ teflon tape this weekend. They don’t sell it locally, and it costs maybe $2 online, plus $8 shipping. Eh, I can make do with cutting 1/2″ tape down the middle, as it’ll just peel apart with a starter cut, although this goes against my nature.
If I could use the kind of fittings that seal with a single rubber grommet or o-ring, I would, but they only make those for the smallest fitting sizes. There’s a new kind of “universal thread” fitting that has grommets across the line, but they cost a lot more and are tough to find in stock.
3. Push-to-Connect Fittings
Push-to-connect fittings are quick and easy to use. Except tube ends need to be perfectly straight. And once you remove a tube from a fitting, you have to cut the end before reseating it. If you don’t have perfect cuts, or reuse tubing, there’s a good chance of an air leak.
Do you know how hard it is to perfectly cut 5/32″ tubing, even with the right types of cutters?
Well, at least they’re not as much of a nuisance as barbed fittings.
4. Quick-Release Connectors
There are many different stands for quick release fittings, and I can never find the right one that I need.
I switched some stuff over to Legacy color-coded quick release fittings. I bought some at Amazon, and wish they were easier to find locally. Bad news is that the ones I bought (Type D) don’t work with more common standards, such as general purpose Type M.
For the recent small-tubing projects, I have a pair of inexpensive plastic-bodied disconnects ready to go.
5. How Tight is Tight Enough?
“Hand-tight and then a little more.” Sometimes a hand-tight fitting leaves too much thread sticking out, so I pull out a wrench. But then is it too tight? Teflon tape tends to slick things up, which is good and bad.
What bugs you about compressed air and pneumatic systems?
Farm equipment many times have “O” ring fittings instead of tapered pipe thread. One problem is you have less wiggle room to get the angle right. This is hydraulic fittings but theory is the same.
I always use pipe dope with tape, seems to provide some lubrication. I use the stuff that doesn’t harden.
Soapy water applied with a brush finds most leaks.
The G 1/4 BSPP fittings of my old water cooling setup were all straight threaded and used O-rings for seals. I sometimes use silicone grease or similar as an extra precaution. Unfortunately that wasn’t an option here.
I was going to suggest an ultrasonic leak detector to find the air leak. As I was searching for a link to post I saw the price they are selling for and it is not in most people’s budget. The one I have is 474.00 now, I only paid a hundred for the same model about 6 years ago.
Three rounds of teflon and some pipe dope and you will have no leaks. Get Leak Lock (Highside Chemicals) pipe dope and use just a little bit on the tip of the threads, no need for a lot when a little goes a long way.
For mission critical applications, I generally dispense with the teflon tape and use a teflon based pipe joint compound. Tape has been my go to for quick fixes or for temporary situations, but not for something of a permanent nature. Nothing like having a small thread of tape off the end of a fitting finding it’s way into a check valve, or solenoid valve, to frost your day.
Speaking of check valves; I had a fully tested system losing pressure after setting up a new compressor, only to find that the check valve on the compressor to be the culprit (not due to tape in that instance). All it takes is some small piece, or sliver, of manufacturing debris caught in the seat of the valve to ruin your day.
Good luck with your project.
Cheers to that. My dad makes a point to not use Teflon tape on air fittings for that reason. Something I’m sure he learned as an industrial mechanic.
Funny how little details that burn us once will stick with us our whole life.
If you think air is bad – try plumbing up a hydrogen line.
With threaded water pipe tightening up is not as precise a deal. If you happen to back off just a hair on tightening – you may still have a leak-free connection, With gasses – once you’ve “stretched” the threads – twisting back counterclockwise – even slightly – is a leak waiting to happen.
Is hydrogen as much a pain to troubleshoot as high vacuum? Some bad equipment memories from my college senior year lab course just surfaced. *shudder*
I guess that hydrogen is a problem because of the small molecular size – coupled with its flammability. Some codes/jurisdictions require the line to be placed inside of a larger positively vented outer line. Some codes also require wrapping exterior lines for corrosion protection which complicates leak detection and seems counter-intuitive for a stainless steel line with SS compression connections.
Some SS types get hydrogen embembrittlement. The problem can be worse if exposed to acids (e.g. acidic rain due to local atmosphere). Welds are most susceptible, as well as any galvanic action due to dissimilar metals (fittings, hangers, clamps, etc.)
I know that hydrogen embrittlement can be particularly troublesome in high pressure boiler tubes and nuclear reactor piping. With poor pH control the hydrogen infiltrates the steel and combines with carbon atoms in the lattice. The resultant methane molecules are then thought to collect at grain boundaries and can result in the “fishmouth” blowouts that sometimes occur. I understand that the phenomenon is slightly different for low temperature and low pressure regimes. I’m sure that Stuart would have a better understanding of this.
Is there anything you don’t get into? (:D (:D
Michael S. Jackson
Any of the various commercial/industrial soap-based leak check compounds have worked well for me. My favorite is the (very expensive) SNOOP from Swagelok, but I’ve good luck with all of them.
We use Sherlock @ the hangar, pretty good for leak checking aircraft windows or door seals. http://www.skygeek.com/sherlock-t1-8s-24-sherlock-leak-detector.html
7) lube, as in oil that some tools need, that, when some hangs up in a line, stains when using a blow gun
8) compressor noise
9) using PVC for air lines- it can shatter and become shrapnel
Our big shop had a Sullair rotary vane compressor that was much quieter than the piston compressor it replaced. I’ve also visited a shop with a Quincy unit that seemed very quiet. I’m pretty sure that IR and others also make quiet units
SwageLok. Problems solved. 😀
I’m keeping them in mind for the future. But for now, it was far cheaper and easier to source SMC fittings.
I’ve worked on some really precise calibration gear that had to seal essentially perfectly and I used to work in nuclear power. SwageLok and Parker both sealed very tightly but in my experience, if you are sloppy with anything that has to seal tightly, you will probably end up replacing it. Take your time, closely inspect the parts and make sure everything is clean.
I prefer SwageLok stuff simply because you don’t have to mess with flared fittings and SwageLok works on some plastic tubing. The SwageLok ‘style’ stuff that McMaster sells is garbage.
Stuart–Teflon tape isn’t error-proof. I would suggest you instead use a product like HarveyLoc, a sticky multi-purpose thread sealant for metal threads. I prefer this method over tape, which can cause leaks no matter how carefully you wrap it.
HarveyLoc’s color is a light yellow for the kind that seals gas lines; the stuff for sealing water lines is a light oyster. You can buy an 8 oz. container, which has a brush in its cap, at a plumbing supply store. This stuff never sets up completely, so it moves and flexes as needed over time. If you use this, be sure to wear latex gloves and don’t get it on your clothes; it won’t come out.
If this doesn’t stem the leaks, you may have a defective pipe, fitting or inline pressure gauge which will require some detective work to track down. I’d get a small sprayer with soapy water and spritz down all the fittings and lines (the same as when checking for leaks on your outdoor barbeque). You should be able to see and/or hear any leaks. It may be that you have an old cracked rubber air hose, or possibly the take-up reel is faulty. And how efficient (or leak-free) is the compressor? If it’s an older unit, it may be the problem, especially if you have a long run.
If you can take pressure readings from each hose or outlet, you may be able to narrow down which segment is leaking. And don’t forget to check for an inline filter; it would have a glass trap to remove oil and water from the line, which is another source for a leak.
For finding leaks, I mix some liquid dish soap with water in an old Windex bottle. Spray it on every connection, fitting, etc. my most common place for leaks is actually my quick connectors, I have yet to find any that hold up long-term in shop use. The check valve usually holds when disconnected, but they always seem to start leaking around the stem of the male tip. To top off my annoyance, they don’t seal with an o-ring, but rather a use a specially shaped piece of rubber that both acts as the chec valve seal, as well as the seal around the stem of the male tip. Why not an O-ring seal like a hydraulic fitting? Then I could replace a 25 cent O-ring instead of a $5 coupler.
Oh, and I invested in one type of air coupler, and threw out or ave away any that we’re non-compatible. I do have a little air compressor with two air outlets, one coupler is the one I use on all my stuff, the other is a ‘universal’ coupler, which actually has worked with every tip I have tried with it so far. This is my portable compressor I take along when I help someone and don’t know what kind of tip they have. Every tip I have tried in it will ‘work’ for a job, but some will have a slow leak where they connect. So far, though, the check lave has held when disconnected. Some of the smaller diameter tips fit into it with a lot of ‘slop’, which is why I think some leak just a little: they aren’t being held fully centered and square.
Sorry for the typos, I’m having one of those mornings where I’m all thumbs.
Yeah, use some Rectum, er I mean Rector Seal along w tape. It can only help. But overall I agree w Stuart….however after about 9 years of relatively trouble free service my air system is now a wreck: multiple leaks and a crappy ARO regulator that has always sucked and now leaks like crazy. One key to success: don’t buy anything ARO, and avoid see-through filter bowls as they only crack & fail (can’t help but think of Cannondale when I say crackNfail LOL…..but I digress)
I’ve also had a bad regulator that was leaking. My bane are quick connects. No two different brands ever seem to work together. And who remembers exactly where they got their quick connects last time. The quick connection itself usually leaks too.
I’ve learned to live with a small amount of air leakage. My compressor runs 2-3 times a day even if I don’t use it. In my case that’s actually an advantage. I get water buildup in the heads of my compressor and the valves rust if it sits without running for any length of time. I know it’s not ideal, but letting the compressor run a few times a day is better than taking the damn thing apart every couple weeks.
What bugged me about my compressed air system was the high resistance of quick-connects. Some were worse than others but all were bad and just killed the power of my new impact gun.
After no small amount of fiddling that each time increased my then-new impact gun power but did not fix the problem, I created two air paths. One is strictly for big tools using only GuardAir High Flow connectors on the tank, hoses and tools. The other is the standard Automotive type with no Chinese quick disconnects.
I also created a short GuardAir High Flow to Automotive adapter (but not the other way around). I also threw away all my Chinese quick disconnects, put all the “good” Automotive connectors in one place and the strange ones in a junk box, just in case I come across an air compressor or tank and need to adapt it.
In our shops we had quite a number of air stations – stuck with Milton as our brand for couplings, local regulators etc. We did have quite dry and clean air, however, courtesy of a dual tower desiccant system, good inlet and outlet filtration and an oil/water separator.
When we needed oil for tool performance we added it at the tool station.
The biggest thing that bugs me about compressed air and pneumatic systems is there are not yet enough cordless electric tools to replace all of the things I use air for.
The two cordless tools I need yet are a higher volume air pump for pumping up lawn tractor, car and pickup tires and a 500 ft.lb. impact that uses the standard DeWalt, Craftsman or Ryobi batteries.
Since my lawn tractor supplies its own battery, I use a Viair 88P to pump up the tires.
It takes a very quick energy dump to get up to 500 ft-lbs. Not all older battery systems or any cheaper level battery systems are going to be able to do this- ever.
The Dewalt DCF889 20V Max comes close at 400 ft-lbs. To get to 500 ft lb there is the Bosch HTH181, for more you need the Milwaukee Fuel.
I have had good luck with this product: http://www.mcmaster.com/#5477k11/=xjss9g
For larger pipes, I use this as well: http://www.mcmaster.com/#44945k12/=xjsxm1
I used the stick to build a vacuum test system at work for -guess what- detecting leaks in aluminum castings. It a little more work to apply it than Teflon tape, but it seals better, especially on fine threads where Teflon tape just jams and tears.
I totally sympathize with you on troubleshooting the system. The leak can be anywhere. Fittings are not made like they used to and anything (cheaply) made out of cast metal can be leaky. As others suggested, soap bubble solution is probably your best bet.
You can try smoke tubes, but that is more suitable for negative pressure leaks than very slow positive pressure.
+1 on losing teflon tape. I must have 10 rolls around my garage and house. It never fails when I need it I can’t find it and I am forced to run down to the hardware store to buy a roll.
For as long as I remember, I’ve kept all tape rolls on a long peg or two on the workshop pegboard. Tape (of any sort) one of the few things I haven’t struggled to find when my workshop was a mess.
Dave in VT
Nothing to add, except I love this thread! Glad to see I’m not the only one who struggles with this stuff. I’ve had good luck with fittings made by Milton, especially their Hi-Flo line, although it doesn’t always play nicely with other brand fittings. Unfortunately, I always thought they were made in USA, but not.
1. for most average to small leaks soapy water works well the bubble solution kids play with may work even better for small leaks as the bubble don’t pop as quickly.
2. Regarding leaks on smaller pneumatic fittings (1/8″ and 1/4″) I have found that 2 to 3 wraps of good quality Teflon tape (such as the mil spec stuff from McFaster Carr) and proper tightening usually works alternately I have had good luck with higher grade sealants such as Loctite 565 PST. cheep tape and cheep dope are not worth the risk of latter issues.
3. If cutting small tubing square with a normal plastic tubing cutter is hard you may want to try using a O-Ring cord stock cutting jig such as McMaster Carr 9462K2 and a fresh new razor blade. I recently made a larger version to cut 1.125″ soft neoprene tube cleanly and without any distortion, it works like a dream. cutting 5/32″ tube square should be no problem with this method.
4. QC couplers are another place you don’t want to cheep out on. you can get semi universal ones that will work with ARO, Milton (Industrial), and Truflate (automotive) series plugs. I have a mix of Milton brand ARO series and Porter cable branded universal and don’t have any major air leaks. The biggest issue I have seen with QC couplers leaking is when they are abused. You should take the time to clean the male plug before connecting or over time the dirt, grit and grime will abrade the seal in the female coupler and it will start to leak.
5. Tightness is mostly a by feeling sort of thing. There are too many variables in thread size, thread material, thread tape and sealant to give any good recommendations. the best advice I can give is tight enough to seal without leaking but not too much more. it is usually easier to tighten a but more that replace broken and stripped parts. Unless you are working on things that will be inaccessible after they are assembled or placed into service (things that NASA would build).
Metric fittings especially in push to connect applications
Teflon paste is the business instead of Teflon tape except you find it smeared across everything in the vicinity of the fitting to which it was applied
Trying to time threads when hooking up an elbow to a valve
I am not going to read all these comments but if you are running black iron small air leaks are common. They are fixable though I just ran black iron in my garage and I have a very minor leak not even worth tracing. Tape works but it rubs off as the threads get tight. Thread locker PST works well but it is really for stainless threads. If I dont want it to leak I weld it.
I’ll have to check that out, thanks! I wonder if there’s a different formulation for pressurized air systems, as that one seems to be formulated for automotive fluid transfer lines.
I recently got a compressed air system, and I wanted to make sure that I was taking care of it correctly as well as getting the most out of it. This is a pretty unique tool, so I appreciate being able to read so much applicable information about it. Thank you for your advice concerning air leaks, this was something that I was particularly worried about.