This simple mod uses nodeboxes to supply a complete set of 3D flanged pipes.  
Also included in this mod are "valve" and "pump" devices.

Pipes are rounded thanks abusing minetest's nodeboxes ;-) , and when placed, 
they'll automatically join together as needed.  Pipes can go vertically or 
horizontally, and there are enough nodes defined to allow for all possible 
connections.

Pipes come in two variants: one type bears one or more dark windows on each 
pipe, suggesting they're empty, while the other type bears green-tinted 
windows, as if full (the two colors should also be easy to select if you want 
to change them in a paint program).  These windows only appear on straight 
lengths and on T-junctions.

There are no crafting recipes, yet, but you can use /giveme as usual, namely 
"/giveme pipeworks:pipe_empty 999" or so, and then place them as needed.  See 
init.lua for more details.

This mod is intended to be used as a basis or at least as sort of a model for 
something else to build on (perhaps a nicer-looking oil mod?), and does not 
provide any of the code necessary to cause anything to flow through them.  Like 
the pipes, the valve and pump don't do anything useful yet, but you can punch 
them to turn them "on" and "off".  Note that the valve and pump do not rotate 
yet, and the textures and shapes are not yet complete (hence their boxy 
appearance).

Only the full horizontal segments of the old and new pipes, and the 'off' pump 
and valve will appear in your creative inventory.

This mod is a work in progress.

Please note that owing to the nature of this mod, I have opted to use 64px 
textures.  Anything less just looks terrible.

If you don't need the old node names from the previous version of this mod, 
edit init.lua and comment-out the 'dofile' line at the top.

Dependencies: None, but your copy of Minetest must be newer than git commit 
1788709e2d for correct handling of nodeboxes and texture rotations (otherwise, 
the pipes will still work but will look wrong).  0.4.2-rc1 will work fine if 
you don't want to fetch from git.

License: WTFPL (applies to all parts)