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Thread: Need Help With Sealing Compressor Fittings....

  1. #1

    Need Help With Sealing Compressor Fittings....

    So I've been having issues sealing the joints of my new compressor fittings. I've reworked just about all of the joints, first using tape, then using dope, then using tape and dope. Weird thing is, the first 2 or 3 joints out, before the ball valve, tested fine right after I did them, however they failed over the course of a few days. I'm testing the joints using dish soap and water, however it seems the soap dissolves the dope or at least it looks like it does.
    Is there a best way to seal the joints? In the past, I've always used tape on joints and didn't bother testing or checking for a pressure drop. With this new 175psi, 60gal compressor, I want to be more careful about the joints. With the ball valve closed, should the tank maintain its pressure indefinitely or am I expecting too much?

  2. #2
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    Quote Originally Posted by Derek Arita View Post
    So I've been having issues sealing the joints of my new compressor fittings. I've reworked just about all of the joints, first using tape, then using dope, then using tape and dope. Weird thing is, the first 2 or 3 joints out, before the ball valve, tested fine right after I did them, however they failed over the course of a few days. I'm testing the joints using dish soap and water, however it seems the soap dissolves the dope or at least it looks like it does.
    Is there a best way to seal the joints? In the past, I've always used tape on joints and didn't bother testing or checking for a pressure drop. With this new 175psi, 60gal compressor, I want to be more careful about the joints. With the ball valve closed, should the tank maintain its pressure indefinitely or am I expecting too much?
    I sealed with a good quality tape. When I used sealer compound some connections leaked.

    Instead of dish soap and water I always test with bubble solution, bought a gallon for $1 at the end of the summer one year. It gives better bubbles with even very tiny leaks. I use it for tires too.

    If there are no external leaks and the tank still leaks down perhaps there is an internal leak. Mine holds the pressure, at least the times I checked after several days. IR 5hp dual stage 60 gal.

  3. #3
    Personally, I like Loctite 565 pipe sealant with teflon. It applies easily and allows for some immediate adjustment (teflon tape does not). Properly tightened fittings will seal instantly to moderate pressures. For maximum pressure resistance and solvent resistance allow the product to cure a minimum of 24 hours.
    Lee Schierer
    USNA- '71
    Captain USN(Ret)

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  4. #4
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    I was once told by a boiler guy and union pipefitter that one of the questions on the pipefitters' licensing exam was "Teflon thread tape is an acceptable thread sealent. True or False." The correct answer is False as Teflon thread tape is considered a lubricant and not a sealant. I have stuck with that bit of knowledge for a long time, but have since come to learn that several wraps of teflon tape, applied correctly, can seal threads. I always try to buy thicker teflon tape when possible so as to stack the odds of it actually sealing the threads in my favor.

  5. #5
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    For NPT joints I like the teflon dope in a brushtop can. These are all NPT threads? Other types need oil and never any dope.
    Bil lD.

  6. #6
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    What Pipe dope, and what tape? There are many. I used tape and dope on one 175 psi compressor, years ago, and it has never leaked since. Either by itself would not do it. That was with the thin white tape though. Since then, on other compressors, I've just used a non-setting sealant. I'd have to look to see which one it is, but can if you need me to. I don't like for them to leak either.

    Did you try tightening any leaking joints any more while the bubbles were being generated?
    Last edited by Tom M King; 06-29-2019 at 6:42 PM.

  7. #7
    Tom, when I used dope only, once the joint was tight, it was physically locked, like bottomed out. With the tape and 4 or 5 layers, I suppose I could have tightened further, although I was cranked down as far as I dared. Maybe I'm just not strong enough or have enough torque on the joints.?.

  8. #8
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    Something doesn't sound right about a joint bottoming out. I would think you would be plenty strong enough with a wrench. I would try a little more while a joint is blowing bubbles though. You shouldn't have to build up a tapered thread joint like an NPT.

    For my sharpening sink, a guy gave me a bunch of stainless steel pipe pieces that he had used for some beer brewing setup, that he quit bothering with. A couple of those long pipe nipples had something screwy going on the with threads. They bottomed out, and wouldn't seal. I had to take those out of the system.

    I just looked out in that shop, and this is the thread sealant I used not too long ago on a 10hp, and refrigerated dryer setup, and nothing leaked after the first go.
    https://www.gasoila.com/gasoila-soft...with-ptfe.html

    edited to add: I really don't think the type of pipe thread sealant should matter, or at least, not to start with. Did you give it any time to set before pressurizing the system?

  9. #9
    Quote Originally Posted by Tom M King View Post
    Something doesn't sound right about a joint bottoming out. I would think you would be plenty strong enough with a wrench. I would try a little more while a joint is blowing bubbles though. You shouldn't have to build up a tapered thread joint like an NPT.

    For my sharpening sink, a guy gave me a bunch of stainless steel pipe pieces that he had used for some beer brewing setup, that he quit bothering with. A couple of those long pipe nipples had something screwy going on the with threads. They bottomed out, and wouldn't seal. I had to take those out of the system.

    I just looked out in that shop, and this is the thread sealant I used not too long ago on a 10hp, and refrigerated dryer setup, and nothing leaked after the first go.
    https://www.gasoila.com/gasoila-soft...with-ptfe.html

    edited to add: I really don't think the type of pipe thread sealant should matter, or at least, not to start with. Did you give it any time to set before pressurizing the system?
    Tom...honestly, no I didn't wait. When I finished with all the connections, I pressurized the system. I didn't know I had to wait.

  10. #10
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    I was reading specs on them a little while ago, and for Rectorseal no.5, which is a pretty standard one, and one of the weaker ones, it says it's good up to 100 psi for immediate use. I think most ask you to wait 24-48 hours for high pressurization. Read the bottle of whatever you have.

  11. #11
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    Many of the Chinese made fittings have bad threads. You really should run a tap or die over them to clean them up before use. Sometimes British threads end up on them with no taper.
    Bill D

  12. #12
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    Quote Originally Posted by Bill Dufour View Post
    Many of the Chinese made fittings have bad threads. You really should run a tap or die over them to clean them up before use. Sometimes British threads end up on them with no taper.
    Bill D


    https://www.youtube.com/watch?v=-yGRgv2flfs

    Pipe Thread Sealant.jpg

  13. #13
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    Quote Originally Posted by Derek Arita View Post
    So I've been having issues sealing the joints of my new compressor fittings. I've reworked just about all of the joints, first using tape, then using dope, then using tape and dope. Weird thing is, the first 2 or 3 joints out, before the ball valve, tested fine right after I did them, however they failed over the course of a few days. I'm testing the joints using dish soap and water, however it seems the soap dissolves the dope or at least it looks like it does.
    Is there a best way to seal the joints? In the past, I've always used tape on joints and didn't bother testing or checking for a pressure drop. With this new 175psi, 60gal compressor, I want to be more careful about the joints. With the ball valve closed, should the tank maintain its pressure indefinitely or am I expecting too much?
    Derek
    Dope and Teflon together are going to be problematic.
    There are a zillion formulations of pipe dope and it is very important to know the properties of the dope that you are using. most of the dope in a big box store is aimed at low pressure, fluid applications. You need to seal against a higher pressure "gas" applications.
    The best sealant I have found that is easily available in big box stores, is the "yellow" tape for propane and natural gas use. It has to be rated for tank pressures which are higher than what you are dealing with. I know that there must be something to it's properties other than just teflon and colored yellow, because it changes color and sticks inside the threads, unlike "white" teflon tape
    Here are a few tips
    -Clean all threads with lacquer thinner, or acetone. Get the old tape, dope, and machine oils out of those threads.
    -Use high quality brass NPT fittings. Your tank is carbon steel, you want the fitting to be the sacraficial material and not the tank. You need fittings that are softer than the carbon steel.
    - An NPT fitting should never bottom out. Something is wrong if it does. If you need to heavily wrap a fitting to "take up slop", something needs to be replaced. If this doesn't solve the problem, there are epoxy thread sealants, both liquid and solid, that can make up the slop in poorly machined, or damaged fittings.
    - Soap and water is "okay", but get a bottle of leak check or "Snoop" to look for leaks.
    - If your sealant has a cure time, abide by it.
    - Many "fluid" sealants are an aneorobic cure. They cure in the absence of air. The sealant left outside the joint will be soft and sticky, the sealant inside will harden. Don't look at the excess material on the outside and think it is the same inside the threads.
    - In industry, liquid "pipe dope" type sealants for gas applications are normally avoided. They can stay soft and eventually make it to the regulators and clog up orifices and regulator filters.
    - The "bung" on the tank that you are attaching your first fitting to, does not get "cranked down". It should have an O-ring, or gasket seal. If you tighten it to much the O-ring, or soft gasket will deform and you'll get leaks.
    - Yes, your tank should maintain pressure indefinitely. However, as the tank heats up and cools down with ambient conditions, the pressure inside the tank will reflect this. It's not uncommon in the winter for me to see 10psi swings in static tank pressure. My tank is kept pressurized all winter long with little to no use, and it maintains pressure. ( My tank is always left pressurized actually. )
    Last edited by Mike Cutler; 06-30-2019 at 10:13 AM.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  14. #14
    Mike, took some of your advice and got some yellow tape, leak finder and some stuff called True Blue...said it was for gas, among other stuff. I also got a new 3/4 nipple, just incase. I let the old made-up fittings set over night, just to see. Charged it up this morning and used the leak finder on it. Wouldn't you know, no bubbles. So, I discharged the tank and I'm going to let it set a day or two longer before I recharge the tank. Hopefully, everything stays put. I also never considered that the charged air may cool and show less pressure. Also, to throw in another wrench, the main gauge on the tank is kinda hinky and does fluctuate when I tap on it.
    I did watch the vid, along with others and they were informative. One of the problems is, of course, how much do I crank down. Now I know, I shouldn't have to crank down till it locks up. Somewhere along the way, is tight enough and that's where the tape and dope should be doing the sealing...right?

  15. #15
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    Derek
    How much to tighten a fitting is kind of subjective. I personally like to leave some "room" to take up the fitting if I need to.
    A high quality, machined, NPT, fitting will probably be about three quarters to one full turn from hand tight. After that you risk stretching threads and then the fitting is toast.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

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