A clerk at my local Ace Hardware told me to use Teflon tape on the
pipe threads but not the compression fittings. I'm trying to stop a
very slow seepage from the couplings and flex hose surrounding a
quarter turn shut off valve serving the cold water faucet to a
Is this advice correct?
I just changed a quarter turn valve behind toilet. Did not replace
compression fitting on copper pipe as I would need to remove toilet to cut
the old one off. I used teflon paste made for gas line work, it is thicker.
No leaks. WW
My own experience begs me to differ with you on that point.
While it may not be kosher, I've stopped slow leaks on compression
fittings by trimming a few inches of teflon tape down to about 3/16"
width and wrapping that narrow strip around the stub end of the tubing
adjacent to the compression ring. When reassembled the teflon tape gets
squeezed into the space between the valve outlet, the stub end of the
tubing and the compression ring, sealing whatever path was leaking just
YMMV, but it's worked for me at least three times already.
I've got to agree with Jeff.
Yes, compression fitting have straight threads and a compression
sleeve to do the sealing
BUT telfon tape or teflon dope can be used on stubborn fittings that
refuse to seal.
I used to to be a purist and replace fittings that wouldn't seat
properly & seal.
I took the tip from a master plumber who I saw using teflon dope on
compression fitted angle stops.
I asked him.....
"Hey Robert, what's up with the telfon dope on the compression
They're supposed to be metal to metal contact....no dope required."
To which he replied....
"Yeah, I know but it seems like my crew and I used to invariably get
one to two 'leakers' out of a houseful of compression fitted angle
stops. Often requiring the valve to be replaced or worse...... a call
back the day. Since I've switched to teflon dope; leakers, no call
His experience was hard to argue with. He & his crews probably do
more angle stops in a couple months than I have in my entire life. I
switched to doping compression fittings. Goes against my engineer's
sensibilities but it works.
The dope or tape doesn't seal the straight threads but serves to help
the compression sleeve & seat to seal. Maybe modern compression seats
& sleeves aren't as well made as years ago and they have
imperfections / deformities that need the dope?
Now to address the dope or tape question.
"it's a lubricant", "no, it's sealant".......... "no, it's both".
They are sealants that provide come lubrication BUT their main purpose
is "sealant", here's why.........
Standard tapered pipe threads (NPT) will NOT seal without a sealant.
Yes, they get torqued together BUT no matter how well lubricated or
how much they're tightened, they will NOT completely seal.
BTDT....... YEARS ago I did the experiment of trying to get NPT pipe
threads to seal with lube alone; they can't, they won't. The
internal threads & external thread have a bit of clearance so even
when they are "tight" there is an volume beyond the tip of the
external thread, ending in the valley of the internal thread.
This "gap" between the tips & the valleys is where the pipe dope needs
to be, to seal the NPT threads.
Without tape or dope, you'll always get a bit of leakage; back
through that spiral path.
The good new is, a lot of domestic water carries minerals that will do
the job of pipe dope..... eventually. :)
In fact, check out the MSDS for Loctite HVAC Blue
The non-volatile part is calcium carbonate....... HVAC Blue is user
applied "hard water deposits" :)
Now for those who really want to "geek out".... there are "dry seal"
pipe threads (NPTF) but if anyone ever suggests that you use them, I
recommend asking them to "show me how".
I've used them, YEARS ago and can attest, they are nasty & a real
PITA. Do whatever you can do to avoid them. The are close tolerance
and meant to create a true interference fit. The whole point is "seal
without sealant". Made for military or applications where sealants
(dope or tape) are a no-no.
Bad enough in plated steel, in stainless they are a nightmare.
Yes it is. You probably need to replace the brass compression ring.
If you do no thave some extra length in the line it is on you will
need to replace that piece as well. Compression fittings can be
reassembled but not infinitely.
See the Wikipedia article on compression fittings to understand how they
work. Most important thing with those is to be clean and gentle with them.
Pipe threads are tapered according to the National Pipe Thread (NPT)
standard. See also the Wikipedia article about that. You need teflon
tape or a goopy sealant and a small pipe wrench to stop the leak there.
Actually teflon tape does both. Before teflon tape a waxed linen
thread was often used to accomplish the same thing. Wax alone would
not do the job and it is an excellent lubricant - and plain linen
thread would just shred, doing no good at all.
Sort of. Teflon tape is indicated for tapered threads where its lubrication
properties help to tighten the contact, thereby deforming the threads to
create the seal.
Parallel threads do not deform and no amount of tightening will cause them
to seal. To seal a parallel thread, you need some additional form of
sealant: a gasket, deforming ring, sealant, etc. Teflon tape does no good at
all on parallel threads. Nada.
Even where indicated, tape can be a hazard. Over-use can prevent the threads
from deforming, minimizing the seal leading to leaks, and bits of tape
hanging in the passageway can break off and compromise downstream valves or
I have seen varying success using it on old compression fittings but
you wrap the ring, then everything else you said, happens. (The barrel
and ring slide more easily and deform to seal)
I have also seen a single turn on the threads, just for lubricating
them when the fitting is old and crusty.
Better is always to cut it off and start over if that is an option.
On Mon, 31 Jan 2011 20:47:43 -0500, firstname.lastname@example.org wrote:
Never heard of the waxed linen thread, but I used pipe dope long
before Teflon came around.
Think it was a combination of linseed oil and red lead, but I read
that somewhere and won't stand by it.
Besides, it was always a white or off white color.
The old pipe dope always hardened too.
Any old pipe I ever took apart had rock hard dope.
Didn't cause adhesion, just more force to break the bond.
Looks like there's no museum of pipe dope where you can get the facts.
I did run across a quote of ANSI/NSF 61 standards that says white
Teflon tape is only good to 3/8".
I've been using whatever cheap Teflon tape I have around on up to
3/4" and might have used that on a much bigger header I reworked
when I put a new boiler in at my ma's house.
But I may have used a TFE paste on that.
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