Threaded joints
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Sealing threaded pipe joints.Home owners often need to seal pipe joints and its never worth calling a plumber to seal a single threaded joint. This task also falls well within the capabilities of most DIY enthusiasts :-). This little section has been written so that you can do it well! Dont get too ambitious though - stick to the ends of pipes - dont try to re-seal a conection mid way in a steel pipe - that's what I do to pay my bond :-). Standard disclaimer applies - you are on your own. I accept no liability or responsibility for things that you do at your own risk. The most common places that you will come accross these connections is on taps valves, toilets and washing machines. Note that modern taps mostly use steel braided hoses that are sealed with 15mm washers. These are easy to sort out. Get some new washers from your local hardware store. Close off the stop valve and loosen the leaking joint. Remove the old washer with a sharp object and insert the new washer. Replace the connection - dont make it too tight and dont twist the pipe! Switch on and check for leaks. It may be better to replace the flex pipe with a new one. They are cheap enough - but make sure you get a SANS/SABS one. This is a potential time bomb if you get a cheap and nasty and it fails while you are in Plett! Joints that I am discussing here, that are sometimes problematic are those that rely on the thread to be water tight. For example where a tap screws into a standpipe elbow out in the garden, or where a stop valve screws into a wall elbow. In these cases you need to use either plumber's (PTFE) tape or hemp. I really dont know why they call the PTFE stuff "plumber's tape" because most of us detest the stuff in favour of good old hemp. PTFE does work if you use it carefully though. I just find that hemp works better. Mainly because it swells when it gets wet. A joint that drips slightly will seal itself after an hour or two. I will explain both methods. Seal with plumbers tape - clean the threads of both the pipe and the socket well. Wrap the tape clockwise (looking down the bore) around the pipe threads until you can only see the "bumps" of the threads rather than the threads, In other words - use lots of tape. The biggest problem with this stuff is that you never seem to put enough tape on. Unfortunatly the "gaps" between the threads of various fittings is variable. There is thus no standard quantity of tape that needs to be wound on. With a bit of practice you can figure out if its a tight or loose joint and then apply tape accordingly. I you find that you have put too much on then you should reduce it a bit and try again from scratch. You dont have to tighten the joint with a 24 inch pipe spanner! Just nice and snug plus half a turn should be fine if the tape is right. Seal with hemp. You should be able to buy a wad of hemp from most big hardware stores. It's very cheap. Good stuff to keep in your toolbox! Clean the threads of the pipe and socket. Pull a "string" of hemp off the bundle in a long strand. Difficult to describe but for a 1/2 inch pipe i would be looking for a piece about 20cm long, loosly the diameter of a pencil that will compress into a diameter of a piece of string or wool when I start winding it on the pipe. Starting at the end of the pipe wind the hemp along the threads in a clockwise (looking down the bore again) direction. The hemp "string" thus follows and fills the threads! Wet your fingers and turn the hemp clockwise to tigten it on the threads, Screw the pipe into the socket. Again all joints have a variable "gap". Some joints will require more hemp, some less. If the pipe screws in too easily then you have too little hemp. If it only goes one third of the way, then too much. You may have to do it again. A little more practice is required with hemp but once you have it, your joints will seal first time every time! If you are sealing a galvanised pipe you may consider using stuff called "Stag". It's a compound that you use with hemp that glues everything together. Joints done with hemp and Stag seldom leak and the corrosion potential is reduced. Rusted and corroded Galvanized pipe joints - getting them apart! This can be tricky, because the rust has often fused the threads together and you can only exert a limited force on the old pipes before you crush or break them. In these cases I always use a blowtorch to heat the female part while trying to keep the male side cooler with a wet towel. The steel needs to be made very hot - up to dull red in some cases. This invariably releases the grip on the threads and the total force required to loosen the joint is considerably reduced due to the thermal expansion of the female side. Other tools needed are 2 pipe wrenches - often called a "bobejaan" in SA. Cutting Threads. My short answer is forget it. It is seldom possible to be able to get to enough of the rusty old pipe so that the threading machine works. Even if you can get to it, the pipe invariably collapses because of rust. Give me a call if you get into this situation. We have creative ways of fixing pipes that seldom involve cutting new threads!
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