Teflon tape a no no?

[Willis Fecon Bushhogging]

I was just reading another article here and people are saying Teflon tape is a no no in connections.

This is odd.. A number of hoses have teflon on it. I have not found any teflon on elbow connectors to pumps and such. My hose dealer told me not to use teflon on a "fresh" connection, but if I remove a connector from a hose and replace / re-attache then I need to teflon up.

Any advice always apreciated as I have some stuff to mess with when I get back to the farm.

I know that most people are smarter than this, BUT dont do what I caught one of my guys doing a few months ago. I told him to replace a leaking hose, I gave him the new hose, this is a hose with male and female ends (no pipe thread ends) we were at the shop, so all the tools and supplies were available. Being it was a simple job, I went and done something else. I returned and found he had used teflon tape on the male ends of the hoses, I didnt notice this, until I started up the unit and it leaked. The tape, was preventing a good seal on the male/female connection. I instructed him that only male ends that screws into a unit, gets tape. I know there are lots of different applications, that changes this instruction, but for the most part, its the true way to do things (at least as I was taught 40 years ago)
Just my 2 cents worth

 

[canoetrpr]

So I did up the one male pipe fitting while I was waiting for some paint to dry. 1.5 wraps - one thread up. Not sure I got it tight enough.... we'll see if it leaks.

Couple other related questions:

- For some of the JIC connections that I tightend today, after doing that I wondered if I should have put some oil on the fittings befor tightening? They are tightened now - guessing I should not undo just to get oil on them.

- As a rule of thumb, how much should one tighten a fitting so as not to overtighten for hydraulic fittings- JIC, ORB, NTP - is there a difference?

I was working on getting my air compressor set up today and found that here was a slow leak on almost all of the connections made. I had to tighten them all a fair bit further than I would have thought I would have to to get a seal.

Final comment - why the heck do they still make stuff with NTP fittings????? I'm a noob to hydraulics but its pretty clear to me after working with JIC and ORB that they are waaaay superior. What sucks is that it is pretty hard to not have to do NTP on a something when you take on a project. In my case it will be all the QD's and one fitting that returns to the tank.

Pretty dang sure my cylinders will also have NTP on them and my pretty new Kubota has got a number of NTP fittigngs even on the hydraulic block it seems. Odd...

 

[Wayne County Hose]

Canoetrpr, you are smarter than you lead us to believe. You, an admitted hydraulics noobie, can tell that NPT is from back in the neanderthal age. It should have been left there. In my opinion, it should be outlawed. NPT was one of the first threads developed to make a seal. It is the cheapest to manufacture as the tolerances are measured in hundredths of an inch rather than thousandths.

The only reason I would put anything on a JIC or any other non-npt fitting is for corrosion protection. A little oil won't hurt, especially if you blow a hose 5 years from now. As far as torque goes, there are torque values for every fitting. JIC and flat face o-ring are X many hex flats after finger tight. Different values depending on the fitting size. This is where a hose and fitting catalog comes in handy. When you see a new machine, you may notice lines down the fitting flats made with a marker or paint pen. They assemble everything finger tight, make a mark down both fittings, then turn the one X amount of hex flats.

They way you did your air compressor is the way I do my npt. Tighten it a fair amount, run it, tighten anything that leaks until the leak stops.

 

[SPYDERLK]

So I did up the one male pipe fitting while I was waiting for some paint to dry. 1.5 wraps - one thread up. Not sure I got it tight enough.... we'll see if it leaks.
[Snip]
Final comment - why the heck do they still make stuff with NTP fittings????? I'm a noob to hydraulics but its pretty clear to me after working with JIC and ORB that they are waaaay superior. What sucks is that it is pretty hard to not have to do NTP on a something when you take on a project. In my case it will be all the QD's and one fitting that returns to the tank.

Pretty dang sure my cylinders will also have NTP on them and my pretty new Kubota has got a number of NTP fittigngs even on the hydraulic block it seems. Odd...

For NPT the word is utter competence of the connection at lowest manufacturing cost. Mostly a PIA for hoses, they also only present slight savings there. However in joining to cast parts they present real cost benefit. There doesnt have to be thread to sealing surface alignment as with the others. All thats needed is standardized taps and dies. The tapped hole doesnt have to even be perfectly perpendicular to the entry face. If the thread forms are correct - screw it in tight and it will seal. When the thread forms arent perfect, tape or some filler is a must. You make the conversion to the modern fittings immediately at the casting. The bad thing about NPT is the tremendous splitting force it applies as it seals - its a circular wedge. The threaded female must be designed to withstand this in addition to service pressure. When you use teflon you dont have to tighten as tight. You dont have to force it past the point of metal to metal contact to much higher distortion in order to seal. When teflon use is tailored to the fit by feel you get a good joint with less splitting force. This requires much less torque. You can get in real trouble cranking on a teflon joint as if its dry.
larry

 

[3RRL]

Canoetrpr, you are smarter than you lead us to believe. You, an admitted hydraulics noobie, can tell that NPT is from back in the neanderthal age. It should have been left there. In my opinion, it should be outlawed. NPT was one of the first threads developed to make a seal. It is the cheapest to manufacture as the tolerances are measured in hundredths of an inch rather than thousandths.

Wayne, although I agree with the NPT thread fittings being hard to work with, but what you said "bolded" above is NOT a true statement.
I know you have a hydraulic service shop and have helped many here with hydraulic questions, including myself. But you obviously don't know your manufacturing details regarding NPT threads. If the tolerances were in hundredths of an inch, it would be possible where the male and female would not even start to fit together. I've attached a scanned page out of my Machinery's Handbook that shows the tolerances as plus or minus .003" of an inch. The table shows dimensions in 50 millionths of an inch for calculating purposes.



I used to design and build plastic injection molds for molded pipe threads, not just NPT but BSP as well s many other thread forms. In my molds, the steel dimensions I use are limited to 1/10 of the tolerances. So I have to hold the threads to plus or minus .0003" or 3 tenths (3 ten thousands of an inch). This is to provide the molder a window of processing the actual threads within tolerance.
Some of those molds cost in the hundreds of thousands for a 4 cavity fully automatic unwinding tool. NPT may not be the "preferred" connection, but it is not exactly "stone age" either...especially in manufacturing them. I have no idea but a WAG would be there are still billions of NPT connections around used everywhere.

I've always appreciated your input as it is generally very helpful, so don't be offended. But your statement about NPT tolerances needed to be corrected.
For the sake of other readers, please stick to the facts.

 

[SPYDERLK]

Wayne, although I agree with the NPT thread fittings being hard to work with, but what you said "bolded" above is NOT a true statement.
[snip]
For the sake of other readers, please stick to the facts.

Rob, you and I know the truth on this. I hope many others realized that he made an exaggeration for effect -[Im assuming]. The very real possibility that some might take that statement as accurate does worry me. Glad you set it straight. Some of the tolerance excursions will have to be within the tenths or even hundredths,of a thousandth, for this connection to seal easily without really gopping it up!
larry

 

[Wayne County Hose]

Yes, exaggeration was for effect. I didn't know we were being so exacting here. I do know the manufacturing details very well. I also know that this does matter to manufacturing, but to nobody here. I am not offended about being corrected.

My reason for stating it the way I did was that in the world of fitting manufacturing and practical usage, NPT is less exacting than many other fitting styles.When making an ORB port as opposed to an NPT port, the ORB port has much tighter tolerances. NPT is way more forgiving, heck, the 2 pieces don't even have to line up right. Mash it in there and it will work. The specs for manufacturing are very tight, yes, but NPT is the only thread for sealing made out in the shop world. Do you think that all these worn taps and dies are holding the tight tolerances as in the manufacturing world? No way. Out in the field, our worn, crooked taps and dies are holding tolerances in the hundredths of an inch and still making seals and not leaking. So, yes, the tolerances can be in hundredths of an inch and still get a good seal. Don't try that with any other thread style. And that is a fact.

I also believe that anyone other than an engineer would read my post and know exactly what was meant and not give it another thought. I also believe that there are many on this board that sit like vultures and wait to pounce on something like this. This is what offends me.

 

[Wayne County Hose]

Here is my real issue. I did state that NPT was manufactured to tolerances of a hundredth of an inch. Which, admittedly, is factually inaccurate. However, these cheap Chinese npt sets sold by the truckload in Harbor freight and every other jip joint across the world can not make an npt thread with a tolerance of a thousandth of an inch. Yet, for the millions of threads they have made throughout the world, they have been extremely successful. So yes, npt is being made all over the world with tolerances of a hundredth of an inch. Even the good sets don't hold their tolerances. This is my issue, engineers not knowing what works in the real world. Anyone that believes that npt must absolutely be made with tolerances to the ten-thousandth or even the thousandth of an inch is absolutely off their rocker.

So, here it is. Do you not know what you are talking about, or, were you sitting like a vulture waiting for an opportunity.

 

[Skyco]

Being a vulture here for a moment-
WayneCountyHose- are you new to the internet? Anyone who has been around on the net any length of time, particularly when addressing technical specifications, should KNOW they will get jumped if they mis-state something.
This is actually a GOOD THING.
Just for the record I agree "hundredths of an inch" tolerances as you posted are just not so...

 

[3RRL]

Larry and Skyco,
You and I are on the same page and for sure.
I knew what Wayne meant regarding the NPT fittings vs ORB or JIC. There are exaggerations and then there are misstatements to reinforce the exaggerations. I'm sure you've seen that I rarely make controversial or nit picking posts too, but I'm replying again out of principle.

Wayne,
Sorry to have ruffled your feathers a bit, but I am not a vulture waiting "to pounce on something like this." I presume that statement was meant for me. "Anyone that believes that npt must absolutely be made with tolerances to the ten-thousandth or even the thousandth of an inch is absolutely off their rocker." Well, I must off my rocker then. I posted a page out of the Machinery's Handbook, so take it up with them. The books specifically states the tolerances of all threads. I posted what I had to do for the plastic injection mold tolerances. BTW, it's easy to do with the right equipment. The inspection equipment is much more expensive.

Now you're digging a pretty deep hole. I was going to leave it alone until I read your last post. "So yes, npt is being made all over the world with tolerances of a hundredth of an inch." You would have us believe you are the sole expert on thread tolerances now? Why, because you own and operate a hydraulic shop and that makes you an expert on tolerances? IMHO, you are just an end user of those threaded fittings as I see it. You don't make or manufacture them yourself.

When you say hundredths of an inch what do you mean? 1 hundredth or 10 hundredth or what?...specifically? We know the taper on NPT is 1 degree 47 minutes. So in a half inch (normal thread tap depth on NPT), the taper is .0312" total on the diameter. That means if the tolerance is say plus or minus .02" for example, if the female is made to the minus .02" and the male is made to the plus .02" they would not even start together. And .02" is on the low end of "hundredths" of an inch. You can see if you go to .03" or .04" and up... you get the picture, right? Even at .01" tolerance you could get them to start by .144" ... like two threads engagement for 1/2NPT and that would strip off immediately.

Here's something else to consider.
The NPT threads rely on their thread form and taper to do their sealing job. JIC and ORB do not. They use other sealing methods, specifically a 37 degree taper or an "O" ring to do the job. So those threads don't really need to be as good as the NPT threads. As long as those threads are strong enough to hold the pressure of the hydraulics, so they don't strip or blow off, they are good enough. Their threads can, (could be) sloppier, but the fitting still makes a seal since they use those other sealing methods. They could probably be worse than those worn out taps and dies you talk about and still seal, as long as they can hold the fitting together and provide enough force to make the seal.

I think that was your point about them (JIC, ORB) being better fittings in that respect, that they seal better or easier, not necessarily the thread details and tolerances involved. I would have been fine with that. There are specific ANSI thread classifications and tolerances for all threads. I just didn't want the casual reader coming away with the thought that NPT threads were made as you described. It would be different if you used some tack and stated "this is what I do" or "this is what I think" or something to that effect. But your statements about tolerances are as though they are fact. That is a bunch of hog wash.