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  1. #1
    Gauge is offline Aluminum
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    Not really a machining question, but I find this to be a VERY knowledgable group, so maybe you can help.

    My father has a small pump house which houses a pump used to irrigate his large garden. The problem with this pump house is that it is not heated and EVERY winter the pump must be dissembled and drained, otherwise, the pipes and pump will crack.

    After too many years of dismantling this pump I finally got smart and decided to devise a system that allows the water to be drained from the entire system through a series of drain valves.

    I created a drain system from plastic pipes (Schedule 40 PVC) and used slip by thread connectors to screw the plastic section into the existing iron well pipe, brass check valve and iron pump. I have 4 plastic male thread connectors that I coated generously with Plumbers Pro Dope before screwing them TIGHTLY into the well, check valve and pump.

    I tested my setup and ALL my connections leak at the point where the plastic male threads screw into the metal (well and pump) and brass (check valve) female fittings.

    Most likely I am going to have to cut the plastic out and start over. My question is what can I use on the plastic pipe male threads to absolutely ensure that they will not leak? Obviously plumbers pro dope didn't work.

    Thanks!

  2. #2
    tattoomike68 is offline Stainless
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    good old cheap teflon pipe tape is good stuff, works for air lines and also hydraulics.

    put it on from the tip first and wrap it up with the thread right handed. (if you do it wrong it will leak and come off as you put it together)

    a roll might cost a whole $1.00 if that.

  3. #3
    chevy43 is offline Stainless
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    Was there rust on the inside of the old iron female threads? Any roughness or rust would cut the plastiic up and make it leak.

  4. #4
    tools is offline Hot Rolled
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    On iron threads, I've had better luck with the dope, so that's weird. I'd try the teflon tape. Also, not much more than really hand tight. Easy to strip PVC threads.

    It's considered by many to be the sign of a well organized person to actually use up the whole dollar role, before losing it... Who knows how many partially used rolls of that stuff are hiding out in my shop with the several hundred pencils I never used up either.

    Tools

  5. #5
    KJP
    KJP is offline Senior Member
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    Some folks use PVC cement to make up threads between iron and plastic. They claim that it will not leak, but itís a booger to get the fittings off the metal pipe. The guy that installed my new water softener did this and when I rerouted some of the pipe I actually had to chisel them off. They definitely did not leak.

  6. #6
    tmt
    tmt is offline Hot Rolled
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    Teflon tape is a great no mess solution to your problem. If it will not stop the leak then try Rectorseal #5. Not only will it seal the threads but will lubricate them for an easier disassembly in years to come.

  7. #7
    Joe Michaels is offline Titanium
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    having worked around piping of one sort or another in powerplants and on locomotives and other jobs, here is what thirty odd years of experience has taught me:

    1. A pipe thread is a tapered sharp vee thread. It is intended to be a "dry seal thread". That is, as it is made up, the taper and the sharp vee thread forms combine to make the threads self-sealing- IN THEORY.

    2. If pipe threads are properly cut and not torn, burred, and are "virgins"- having never been together and apart- then the only thing the pipe dope (pipe joint compound) is really supposed to be doing is to act to lubricate the threads and to prevent galling or seizing of the threads when they are made up. The threads, being cut on a taper, will wedge tighter as they are made up. This produces a hard rubbing along the flanks fo the threads. Aside from the friction which is going to occur, there may be a galling or seizing if the male & female threads are similar materials. Older pipe dopes were nothing more than linseed oil + white lead, or linseed oil + litharge, or steam cylinder oil + graphite.

    3. Once pipe threads have been made up, the male threads may tend to spread the female threads a bit. These take a "set". Break the joint apart and reassemble and it may leak. That is when the pipe joint compound ( pipe dope) gets into more of a sealing role.

    That is also where Teflon Tape comes into the act. Teflon tape is a thin film which is supposed to act to lubricate the threads and not migrat einto the fluid int he piping. For potable water, this is ideal- who wants to be putting linseed oil, Permatex, or similar into the drinking water ?

    The downsides to Teflon Tape are numerous and it is simply not allowed on some jobs. Teflon tape is one of the most misunderstood and misused things out there. People tend to wrap it on heavy on the male pipe threads. The result is it shims and wedge/spreads the feamle fitting threads. People tend to wrap that old Teflont ape on and leave some sticking over the lead threads. Get things together and the Teflon tape gets cut by the leading thread. Shreds of Teflon tape wind up in the fluido or gas flow. The result is Teflon tape inside of control valves or insturment needle vavles or worse.

    Get the Teflon tape wrapped on heavy with a cross or two in it on the male threads, make thing sup, and the Teflon tape will tend to extrude and form unevenly on the flanks of the threads. On brass or steel fittings this is not a problem. On PVC threads, it is often the end of any hope of good sealing.

    Teflon tape has its place, but it must be carefully used.

    4. PVC pipe is a whole 'nother story: it is softer and deforms easily. Making up PVC screwed threads to metal fittings gets interesting as the metal threads will tend to deform the PVC if made up too tightly. Add some Teflon tape and a shim on the threads has been added. Once the PVC fittings and pipe are made up with Teflon tape, a permanent deformation of the threads and female tapers may occur. Leakage will follow.

    What this leads to is my attempt to answer Gauge's question as to how one ought to be making up PVC screwed pipe threads and fittings. My own recommendation would be to get a PASTE-TYPE Teflon pipe joint compound for potable water service. If the PVC threads screw onto or into steel, glavnized steel, iron, brass or copper fittings, then use the paste type pipe dope. Apply it to the male threads. Make sure the threads are all cleaned out to remove any shreds of the Teflon tape and any burrs or other debris.
    Screw the PVC and metal pipe threads together by hand. If over about 1" pipe, use a small pipe wrench and just snug things up. You do not need to put a whole lot of torque onto things to have the tapers start wedging and deforming. After things are mad eup, try putting a compressed air test onto the piping if possible. Check for leaks with soapy water. Air will pass thru a tiny leak that water will not. It is easier to fix piping that has had air in it than water.

    OK- assuming you do have a few tiny little pisser type leaks. You can try taking up on the joints (tightening) a little bit, but you must be careful not to start some other joint to leaking. If you used the pasty type of pipe dope, let the piping sit pressurized for an overnite or two. Often, the paste type dope will work out and stop the leak of and on its own.

    Now for the oldtimer's fix. This dates to the days of black iron fittings and steam radiators. It is not according to Hoyle, but may enable you to save the fittings and piping you have. If the fittings have been mauled or spread due to overtightening and Teflon tape, this is a fix which may let a person get leaks dired up. It worked on old steam radiator piping which had been made up using big pipe wrenches, joints made up and taken apart a few times to get the condensate out of heating radiators... joints made up by guys with the idea that the only way to make up piping was to bend or bust a pipe wrench. This spread the fittings and then some. The piping used to leak. The old plumbers had a remedy and the word for it is "Wicking" (or as the old plumbers would say "Wickin'"- not to be confused with the belief in witches). Go into an independent plumbing supply house and find an older counterman. Ask him for a ball of fine wicking or "candle wicking". It is a kind of soft, loosely spun cotton thread. Get some teflon based paste type pipe joint compound (pipe dope). Now you can do what the old plumbers did and probably get away with it. Take your piping apart and clean everything real good. Paint a thin coat of the pipe dope on the first male thread to go together. Wipe the dope into the threads with your finger. Take that ball of wickin and carefully wind it onto the threads so it lays neatly in the "valleys" of the threads. It must not cross any threads. Pull the wickin so it lays in nice and tight with no slop. Make an extra turn or two around the last thread to hold the wickin in place from unravelling. Apply another thin coating of the pipe dope over the wickin. When this is done, make up the threads, bringing things snug, then tighten up by HAND if running PVC threads on metal threads. If over 1" pipe threads, use a small pipe wrench.

    Keep going as you assemble the piping. Remember to use a wrench as a "hold back" so that you do not distrub the joints you already made up as you work on joints further downt he line.

    I learned about making up "used" Dad's Rigid pipe wrenches, Rigid and Reed pipe cutters, die stocks and a few balls of wickin'. We lived in a four family house, so I helped my dad do plenty of plumbing repairs in the tennant apartments and we would get called to help out the neighbors up and down the block. All screwed red brass, or black piping in those days. Still, if it was together and apart, especially if dad saw the wrench marks from some previous do it yourself/gorilla who had tried to "fix da leak", dad knew it had a good chance of leaking. Dad would tell me to wind in the wicking and dope 'er up. In those days we used "Hercules" pipe dope- one type for all uses. When we got done, the joints held good.

    When all else fails on PVC/copper or PVC/Brass screwed joints on my well system, I go get the ball of wickin. I learned about the wickin' when I was a kid, so this is going back 40+ years. On powerhouse work and locomotive work, the wicking is not used. Wicking is for residential plumbing.

    Another oldtime pipefitter's and plumber's tip: Always put a nipple into the un-used female threads in the branch of a tee when making it up. Similarly, put a nipple into the far end of any valves as you make them up. If you don;t and get to tightening, you could deform the tee or valve body. Old steamfitters showed me this years ago and it made sense to me.

    The main thing with any of this work is to take care and make the joints up without geting too rammy. PVC pipe threads simply will not hold up when wedged hard against metal pipe threads. What seemed a normal amount of torque for tightening a brass or galvanized ipe fitting on a similar nipple or piece of pipe will deform the PVC threads. Take the whole run of piping apart if you are havng leaks, inspect it for damaged threads and try remaking the joints using a paste type dope plus wicking. If you work your way along the piping and use a "holdback" wrench to avoid putting any more tightening (or loosening) torque into the joints you already made, that will also help a lot.

  8. #8
    Interpolate is offline Senior Member
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    I like the thicker GAS line teflon(?) stuff for metal to plastic. Find it doesn't tear a easily and will actually be there a bit more in reassembly. Yellow in color, what I've got.

  9. #9
    EPAIII is offline Stainless
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    I didn't read all of Joe's reply so this may be redundant but in my experience, PVC threads are fairly tough and should be tightened with more than hand force. One thing about PVC threads is that they are likely molded and there is a parting line with some (more or less) web protruding. This can create a leak if the joint is not tightened enough to crush it down.

    But don't tighten as much as you would with galvanized or black pipe. More like you would with brass or aluminum fittings of similar size.

    Paul A.

  10. #10
    Gauge is offline Aluminum
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    I REALLY appreciate everyone's replies. I tightened these pipes with a ridgid pipe wrench rather hard. I am surprised I have leaks also. The pipe is 1 1/2" in diameter.

    Another thing that might have happened is that the old iron pipes were REAL hard getting off and I am afraid I might have distorted the "roundness" of the pump flange and the brass check valve when I removed them.

    I am going to go back and cut the plastic pipe and tighten them almost to the breaking point with a wrench. Hopefully that might help and will be my last resort before starting all over.

    The good thing about PVC is that it is not that expensive.

  11. #11
    GregSY is offline Diamond
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    If you have a pump, there must be electricity??

    Why dontcha add a little thermostatically controlled heater to the pump body? Then you don't need to do anything.

  12. #12
    azsort is offline Aluminum
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    Here's my 2 cents:
    I quit using PVC on anything important. Maybe its that here in Arizona it can't handle the heat. Even when its not in the sunlight it seems to dryout and get brittle over the course of years. Plus, you can't take it apart and put it back together without trip(s) to the store. Around here when the water system breaks, you drop anything your doing and work on it. I use plastic on outlying runs but around the pump system that requires maintainance, everything is steel or brass.
    I'm glad to hear someone else doesn't use teflon tape. My experiance on steel fittings is they need lubrication and preservation. Tape may work fine initially, but 5 or 10 years later when your trying to take it apart the threads are all rusted.
    Another tip, don't use female threaded PVC fittings to connect to steel pipes.

    Hot (but dry) in AZ

    Greg C.

  13. #13
    Mike Folks is online now Cast Iron
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    My experience with pipe and plumbing has shown me that PVC or plastic pipe is not conpatable with the loctite brand pipe dope as it will soften the joint and leak in a short time.

    The machines I used to build had brass or copper fittings and pipe dope was used with no problems except when plastic volume gauge was on the control panel the the teflon tape was used very sparingly.

    Mike Folks

  14. #14
    freddycougar is offline Senior Member
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    we at work use a teflon paste made by LOKTITE works for oil,fuel,air , antifreez.....works Very well
    pipe thread not real good for sealing but this product WILL seal it. AND CAN BE DISASEMBLED.
    freddy

  15. #15
    Harley is offline Aluminum
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    I must confess I did'nt read all of Joe's post either but I will say that he's right about the tapered threads and that the dope is only a lubricant. I know the can says its a sealant but trust me I'm a steamfitter.... pipe dope unless its epoxy based is a lubricant. However if you can find the epoxy based dope, it'll seal anything. Be forwarned though........
    We call it the (Red Death). Its usually red for some reason and when found don't bother attempting to dismantle with a wrench. It won't come apart. You can skip the chisel too and go straight to whatever your favorite implement of mass destrustion is take it apart. We avoid it all cost when possible. You'll probably have to look at an actuall plumbing supply to find it also. I've never seen it anyplace joe public usally shops.

  16. #16
    surplusjohn is offline Diamond
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    I used to build swiming pools 30 years ago that had sevearal pvc to galvinized connections that were very leak prone. One job I ran out of teflon tape so out of desperation I swabed pvc cement on the threads before assembly, worked perfectly, no leaks, but impossible to disassemble. I built almost 100 pools that way, no problem

  17. #17
    Habu is offline Member
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    Well, I have to confess that while I did read all of Joe's post, I printed a copy out so I could conveniently refer to it the next time I have to deal with plumbing problems. Thanks for a great post!

  18. #18
    John Garner is offline Stainless
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    Boy, I sure missed where Joe was going with the wickin'; I thought he was going to tell of a technique I witnessed on new work in San Francisco in the late 1960's. Threaded pipe joints were assembled with a water-mixed paste about the consistency of wheel-bearing grease and allowed to set overnight. At oh-dark-hundred the next morning a construction-company inspector performed a pressure-decay leak test, and leaking runs were flagged for rework.

    Rework involved mixing a batch of the water-mixed compound to about the consistency of Vactra #2, brushing a coat of the fluid compound over the joints, and pulling a vacuum on the run. Helped along by the vacuum, enough of the compound would wick into the leak path to seal it.

    My participation in that particular job was VERY peripheral . . . most weekday mornings the piping inspector bought a copy of the Chronicle from me as I headed home after finishing my paper route, and sometimes he and I would chat for a bit while he watched his pressure gage.

    To change topics a bit, the red compound that Harley speaks of could be epoxy but if the work is much over thirty years old, I'd suspect that red lead in a drying oil or a litharge / glycerine mix would be more probable.

    John

  19. #19
    Jon Bohlander's Avatar
    Jon Bohlander is offline Stainless
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    Hi all

    Not an answer to the orginal question but Mr Michael's excellent (as always) post reminded mee of something. You see lots of guys using pipe tape on hydraulic and air lines. That's a bad practice as the tape can get into valves, air tools, etc. causing lots of problems. Loctite 545 is especially made for these applications and is good stuff. This was driven home to me by a maintenance man who I respect very much.

    On the lots of wrappings of pipe tape, I've always been told two wraps is all you need. All this seems like nit-picky stuff but I consider it part of doing a good job.

    jon

  20. #20
    metlmunchr is offline Diamond
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    A sliver of teflon tape will render a hydraulic servo valve useless. It'll jam the spool in a lap-fitted hydraulic directional valve. And it will ruin an oil burner pump just as sure as you put it on any threads in the oil piping. Manufacturers of both oil pumps and servo valves state specifically on their warranty info that anything returned under warranty will be examined for the presence of teflon tape, and if its there, there is no warranty.

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