Tapered Pipe Threads: How to get Tight Joints in a Particualr Direction?

snipped-for-privacy@alum.mit.edu (Doug White) wrote in news:ccqdna8zNYTgAYPYnZ2dnUVZ snipped-for-privacy@rcn.net:

Tape the joints, run it in finger tight, and you still have a good 2-3 turns left before it's actually tight. You can tell as you tighten it up the increase in effort required. On the last turn, position it. Remember to always start at the first fitting and work out and always use 2 wrenches, one to hold the part you are screwing into, the other to screw with.

Use teflon-filled pipe dope, not tape. Tape can get "whiskers" that can screw up pneumatic stuff.

other to screw

Something a suprizing number of shade tree mechanics never learn.

Wes S

A big 10-4 on that from a guy that had to learn the hard way.

Karl

Tape can also mess up steam traps...

I dunno what your usage will be, but for most compressed air tools and accessories, you shouldn't use 1/4" pipe for a supply line. The small ID of 1/4" pipe/hose is too small to deliver proper air flow without experiencing pressure drops from the long, restrictive diameter. I wouldn't consider a 1/4" supply line to be adequate for more than an air brush or some aeration/bubbling operation.

With a tool or paint gun attached to a source with a 1/4" line, with a length of say 25 ft of hose, there will be a significant fluctuation in working pressures at the tool end. The pressure will remain the same as the pressure regulator setting until the tool trigger/valve is opened, then the pressure will drop while the regulator tries to compensate. This type of pressure becomes very evident when a pressure gauge is observed at the tool end of the hose.

If you can't use a tank fitting any larger than 1/4", then a reducer could be used to attach a larger sized supply line to the tank, and the only restriction will be the short length of the 1/4" fitting. It would be best to use a larger sized tank fitting if one is available. You don't say what the tank is, or what the application is that you're contemplating, but air compressor tanks generally have threaded fitting ports/openings larger than 1/4". Using a T at a larger tank port would be beneficial for good air flow and tool performance.

Tapered pipe fittings are somewhat forgiving for placing components in their desired positions. I would also recommend pipe dope/thread sealant (instead of tape, and certainly not silicone RTV sealant). An important rule to remember is to align to the desired positions/directions while tightening only, and not to back up or loosen connections for aligning parts.

Using a die to add thread to pipe of fittings is a bad idea, as it will create poor fitting parts. The taper shape and diameter will be lost on the small end of the taper, making the end too long to fit into female-threaded parts properly.

A swing joint is typically two street ELs connected together, for getting a pipe to change direction in an almost infinite number of positions. Cast iron street ELs tend to be restrictive (and create water puddle points) at the male ends. A less restrictive swing joint can be attained with 2 close nipples and 2 common elbows (although the

Using a flexible, pressure rated hose to begin the air supply line at a stationary air compressor tank, will allow the accessories to be mounted nearby on a wall, and isolate them from the vibration of the air compressor. If the air outlet on a vertical air compressor is on the top of the tank (which may be higher from the floor than a convenient height for the air supply line), the supply line should have separate pressure rated receiver (with a drain) to act as a water catch at a lower position. The air supply line should be sloped back to the water catch (or the air compressor tank, when convenient). This is one reason for most air systems to be mounted high on a wall, with service drops at convenient locations in a shop.

When adding accessories to a portable air compressor, it would be worthwhile to add some support brackets to the motor/pump mounting plate, to support the accessories. This should prevent leaks resulting from fittings loosening from vibration. The hose connector should be mounted to a secure point to prevent stress being applied to the plumbing or accessories, in the event that someone trips/yanks on an air hose, for example).

WB metalwork> I'm plumbing up a compressed air tank, with a regulator, gauge, valve,

As well as systems with fluids and small nozzles. I was amazed at the small pieces of pipe tape that broke free into a system and clogged everything.

If you really want to find out how far you can push the make up on a given pipe and fitting size, clamp a section of pipe in a vise and go to work tightening a fitting onto it. It will surprise you how far beyond "tight" you can go. There's tight, and then there's TIGHT.

As mentioned before, use a good teflon pipe dope and two pipe wrenches when you get down to installing the real thing.

Like the guy who complained to me that his plumbing was leaking, and would I take a look at it, found out. "First of all, quit using that cheesy tape, and learn to tighten it up!" At which point I grabbed the pressure gauge and gave it two full turns while he was stomping his feet and saying I was going to snap it off. It quit leaking, and then I reached in my wallet and pulled out my Union Plumbers card, and said, "Hey Dad, I have the card, you don't. And if you know so much about it, then why did you ask me?"

It's not often a story mentioning a union card makes me laugh...

Apply tape or pipe dope, (pipe dope preferred) screw down hand tight, then wrench around to the desires angle. If it seems loose, go one more full turn. Developing a sense of "loose" takes a bit of practice, but not a whole lot. You can cram pipe fittings down awfully damn tight (as in tight enough your wrench will flex or start to smash the fittings and round off hexes) before developing problems at the threads. But they don't need to be much more than moderately tight to hold pressure with pipe dope. Also, if you have to stack up multiple parts that aren't angle sensitive, like adapter bushings or pipe nipples, screw them all down snug with a wrench, but not much further. That way you leave yourself a lot of slack to play with when you stick on an elbow. Screw the far end of the stack and the elbow together, letting everything in between turn as it pleases. It's not hard by any means. Jump in, slap it together, pressurize it, then spray it all down with dawn dish soap and water and look for bubbles. If you get some, up your concept of "snug" a little. If no leaks, call it good. You shouldn't need a thread die unless you're going to be cutting the pipes.

All good advice. Thread dies are pretty expensive. I made a compressed air manifold recently out of a brass hex bar, and had no problem lining up threads for placing various regulators, etc.