We're short of work these days on the
alarm side so I spent today demolishing some sprinkler pipe as the
sprinkler side of the business is going gangbusters at the moment. I learned just how filthy sprinkler work can be.
While PVC pipe is beginning to be accepted in fire protection business, as a general rule sprinkler pipe is made of metal, mostly black iron pipe of either a schedule 40 or schedule 80 composition black iron. There are three ways the stuff can be put together. First you may weld it, which is expensive, time-consuming and nigh impossible to remove but enjoys the very great virtue of that once you've got it right it won't leak until the pipe rusts out. Welding isn't that common today except when you need to branch a smaller pipe out from a main. Flanges are welded on. The second method is to use grooved pipe with couplings. This is really only useful for pipe 1 1/2" (say 45mm) or larger. They make a little machine that presses the grooves into the pipe. Conduits are then butted against each other and a wide, thick rubber gasket must be slid over to it covers the gap. Cover the whole thing with a two piece compression fitting, and bolt it down tight. Viola, no leaks.
Bu the third and most common way to assemble sprinkler pipe is cut and thread. A sprinkler fitter takes a threader, which may or many not include an automatic oiler, and a set of dies. Select the correct NPT die for the size of pipe you're using, or simply reset the cutting head for pipe size, line up the pipe, cut measure and make your own. This is probably the most common method of installing a sprinkler system, particularly for the smaller branch pipes.
But the thing to remember there is . . . oil. Threading dies are precise and expensive, and will readily break unless cooled by oil. The simple fact is threading pipe necessarily implies getting a lot of oil and and in the pipe. Sure you try to dump it out, but it is impractical to clean it all off. Which means that sprinkler pipes, once full, are filled with a mix of brackish water and oil held there under pressure until the system is tested or a sprinkler head pops. No circulation at all. As the correct way to install a drop ( what they call the pipe that leads to the spraying head in your office ceiling) it to run a pipe straight up, add short horizontal section (as needed) then turn the pipe back downward to the specified height. Say ceiling height. Which means there is always some water left in the pipes, even after you've drained the system.
The pipes are screwed together with pipe dope and tightened until they do not leak. Today's job involved removing a now-banned pipe dope made by a company called Permatex. Permatex pipe dope seals very, very well, but it dries up in the threads, meaning you can't unscrew them once they have dried out. Which is why it's no longer code legal. Normally a 14" pipe wrench is used to install 1" pipe. With permatex dope, a 36" pipe wrench is required to unscrew them. It's big, heavy cast steel wrench with forged and machined teeth. Unthreading 2" pipe? In your dreams! Use a sawzall, band saw or pipe cutter to get it apart. Bring plenty of spare blades I know this because I tried to unscrew several Despite my substantial personal growth, I didn't budge them a bit.
And when you do get it lose you get sprinkler water, black and smelling like sour eggs. If you get this stuff on your clothing, it is ruined. Sprinkler fitters for years have struggled with washing this stuff out and have only failed. Get it on your hands and you'll need a pumace cleaner to get it off. It is foul and nasty, and after coating myself with the stuff today, all I can say is I really hope our alarm work picks up quick.
Why the arm-over? Say you need to replace a sprinkler head for some reason. With the arm-over all you have to do is shut the nearest supply valve, and you can take out the head and only have to catch the water from the individual arm over. If you don't do the "up and over" you have to drain the entire system before working on any part of it.