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Old 10-11-2016, 09:46 PM   #11
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Quote:
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I don't know what kind of equipment you are working on. Before becoming a plumbing apprentice for the past 2 years. I spent 9 years repairing military vehicles. A lot of fittings for hydraulic lines were nptf. We used a special kind of thread sealant . Locktite 545 I believe. But as stated above, I would call manufacturer , and ask what they advise.
Yeah I worked on those type of fittings to and I believe that is what we used. But this is for type 2 diesel fuel, 2" black pipe... NPTF for black pipe is pipe dope and i only use it as a thread lubricant because if the threads are correct it is supposed to make a mechanical seal. Thanks for the suggestion...
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Old 10-11-2016, 09:48 PM   #12
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I would never use Teflon on a fuel line. Most of our fuel lines, we did not use anything. The fittings were designed this way.. Just tighten to the proper torque. How big of pipe were you running? We had hydraulic lines like this as well that went up to 2.5"... Anything bigger we used flanged fittings typically.. Without seeing your fittings, and how it was engineered o specd, I can't say what you should do. I would say Teflon tape and dope would not be something I would do, and goes against what I was trained.
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Old 10-11-2016, 10:03 PM   #13
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This is for a fuel system for a new hospital I was called to come in and take a look at see why there were so many leaks in the new fuel piping. Due to my background in designing and installing fuel systems, reverse osmosis systems and open and closed loop water systems. I have never seen this type of set up by using both pipe dope and Teflon tape on a NPTF system. When i approached the plumber he said that he done this for many years and was trained that way from the union. But in no standard does it say it is authorized to use both and when you are on a federal job at a children's hospital and the diesel generator has to be shut down because leaks start occurring all over the place. So they send some one like me as a 3rd party to find out why this happen. So instead of raking this plumber over the coals i look at every possible way to come to a conclusion and i decided to turn to his brothers and find out why this practice is occurring. When in the NPTF manual it clearly says to not do that and even on the manufacturing bottle of pipe dope or Teflon tape it does not say to use both for a better outcome. As for ShtRnsdownhill I have called many manufacturing companies and even UL's main office and all say the same thing that plumbers should follow the instructions on the bottle. That all products go through vigorous testing phase and the product will do as listed on the bottle. As for me being a plumbing professional, I am...
I have plenty of certifications in plumbing and have designed and built many systems. But I am always interested in learning new ways of doing things and also why some one would veer off of a standard on a job like this with no documentation.
Has less to do with the Teflon tape and dope and a lot more with the install. You are right in the theory that it is a mechanical seal but Teflon helps in the assistance to get that seal. Without extremely clean thread's you will not be able to tighten the joint tight enough before it will gauld. The use of Teflon tape and past is a good practice and aids in the tightening of the joint. Leaks are from joints not tight enough or threads that are to deep from someone that is not setting the threader up right.
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Old 10-11-2016, 10:10 PM   #14
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ACE4548 - Yes you don't use Teflon tape on hydraulic systems because the tape can get into the hydraulic system and cause issues. Also on the hydraulic system once you pass 2.5" you should flange due to pressure.
The system I am inspecting is a 2" black pipe NFPT machined tapered threads and only pushing about 25 psi. When I throw black pipe down on a fuel system I use pipe dope for fuel systems and make sure i get the threads lubricated enough to get the threads in good so i get that good mechanical seal and allow the dope to set for 24hrs before sending fuel down the line. But the question i have is the use of both tape and dope on a NFPT fitting. I have never seen that and nor was i trained to use both. I don't use Teflon tape on a fuel system for one it can allow the Teflon to get in the fuel system and clog inline filters, injectors, fuel nozzles and things of that nature.
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Old 10-11-2016, 10:20 PM   #15
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Wyrickmech - I see where you are coming from on the tape and the dope. But as I look into the NFPT manual it states the following-
NPTF - Pipe threads are designed so that when the threads are mated, they form a mechanical seal and a sealant agent is not required but can be used as a lubricant only.
also when when speaking about straight threads it says not to use tape do to the tape being to thick and can cause the mechanical seal from occurring.
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Old 10-11-2016, 10:28 PM   #16
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Quote:
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This is for a fuel system for a new hospital I was called to come in and take a look at see why there were so many leaks in the new fuel piping. Due to my background in designing and installing fuel systems, reverse osmosis systems and open and closed loop water systems. I have never seen this type of set up by using both pipe dope and Teflon tape on a NPTF system. When i approached the plumber he said that he done this for many years and was trained that way from the union. But in no standard does it say it is authorized to use both and when you are on a federal job at a children's hospital and the diesel generator has to be shut down because leaks start occurring all over the place. So they send some one like me as a 3rd party to find out why this happen. So instead of raking this plumber over the coals i look at every possible way to come to a conclusion and i decided to turn to his brothers and find out why this practice is occurring. When in the NPTF manual it clearly says to not do that and even on the manufacturing bottle of pipe dope or Teflon tape it does not say to use both for a better outcome. As for ShtRnsdownhill I have called many manufacturing companies and even UL's main office and all say the same thing that plumbers should follow the instructions on the bottle. That all products go through vigorous testing phase and the product will do as listed on the bottle. As for me being a plumbing professional, I am...
I have plenty of certifications in plumbing and have designed and built many systems. But I am always interested in learning new ways of doing things and also why some one would veer off of a standard on a job like this with no documentation.
ok then ask the plumber what brand tape and what brand pipe dope he is using and call the makers and ask them, could be defective batch from the factory, I have used both together and rarely have a leak or one develop, so something is wrong somewhere..
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Old 10-11-2016, 10:32 PM   #17
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Wyrickmech - I see where you are coming from on the tape and the dope. But as I look into the NFPT manual it states the following-
NPTF - Pipe threads are designed so that when the threads are mated, they form a mechanical seal and a sealant agent is not required but can be used as a lubricant only.
also when when speaking about straight threads it says not to use tape do to the tape being to thick and can cause the mechanical seal from occurring.
in theory that may be correct, but in reality it will never happen..in a high tech factory with precise threading machines yeah, out in the field threading pipe..not a chance..
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Old 10-11-2016, 10:38 PM   #18
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Mike
Here's a pretty clear definition of the difference between NFPT and NPT threads. It digs a little deeper into the differences between the two.
http://www.cutting-tool-supply.com/T.../NPTVsNPTF.htm

As for testing:
http://www.ring-plug-thread-gages.co...PT-vs-NPTF.htm
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Old 10-11-2016, 11:00 PM   #19
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ShtRnsdownhill- Thank you for your input... But it falls upon the plumber to inspect those threads and to make sure that he meets the standard. So if NFPT says not to use it then you don't because if something happens they are going to fall back and say show me where it says you can use both and when you are talking about federal buildings they will send inspectors and mechanical inspectors to find out what happen. So as a master plumber of your craft, do you follow the standard or do you follow other plumbers that say this is what i have been doing and have no documentation to follow it up and place everything on the line for it.Because remember this is a government building and they will find any way to throw some one under the bus. So if a product says this will seal and it doesn't then they are not going to be in business for long now would they. So now how i was trained was to inspect your threads and then add only pipe dope on black pipe fuel systems because for 1 you don't want Teflon tape because pieces of tape have been known to come off and clog systems and 2nd Teflon tape is to thick and can cause issues with the mechanical seal.Then after you finish you let it sit for 24hrs to allow the dope to cure and then you pressurize your system with air and let it sit and then check for leaks because there is nothing like having a leak either underground and your veederoot system going off do to a detection of a leak under ground or in a overhead of say a hospital. I rather do it once and take the extra time then go back and look like a ass because my stuff is leaking and fork over $.
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Old 10-11-2016, 11:13 PM   #20
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If I was working on a job such as a federal project and they had absolute specs, I would follow them..so what are the specs for that plumber and was he given them for this job? if he didnt follow the specs( hopefully the specs follow the manufactures recommendations for use of their product)then he is liable for the leaks, and either way he is liable for the leaks unless its a defect in the product, and then the manufacture would be liable, could be his threading dies are crap and all the threads are chewed up..not seeing or talking with the plumber and only getting one side and not knowing what your agenda is( are you the govmnt lynch man out to hang this guy) its hard to give you a direct answer on this issue..and if you have all this knowledge and design systems you should be able to answer your own question or find the correct people( manufactures or who put the specs together for this job) to ask these questions..I would say if your building the space shuttle then specs should be followed to the T..but installing oil fuel line is not rocket science and shouldnt be that difficult..why so many leaks..well without having the plumber to ask I cant tell you, I have installed plenty of fuel oil lines with out leaks..one cannot comment on anothers work without seeing it...
and by the way who called you in? to get involved with the project?
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