Sprinkler lines used in alfalfa farming are generally made of aluminium
pipe 4" to 5" in diameter
and fitted with wheels 5' to 7' tall. A sprinkler line can span a distance up to 1280' and provide enough water pressure to load 33 sprinkler heads.
The heads themselves are brass and are spaced 40' from each other as the average range of their spray is 20' which means, with a line 1280' long, a quarter mile of alfalfa can be watered at one time. The heads have levelers on their bottoms, which are cast-iron 2lb weights sprayed day-glo orange to increase visibility from long distances, designed to keep them right side up instead of cock-eyed and spraying straight down. The heads rotate by way of a weighted sprinkler arm attached to a spring which interrupts the stream of water and is slung backwards, then comes back with enough force to turn the entire head approximately an inch and a half.
5' and 7' wheels are designed for 60' intervals between risers, or water spouts, and 6' wheels are for 50' intervals. The wheels also raise the line itself high enough above the alfalfa to keep it from getting caught up in the rotating heads and interfering with the spray or mover engine.
Risers, which are linked to the lines with fat canvas hoses similar to those used by fire departments to direct water from hydrants, are connected to a main line under the ground which is connected to a pump-well or ditch. Older risers were designed to tolerate 100 psi but would rupture if given more than 80. Newer risers are re-enforced with a thick plastic "boot" around the vertical pipe and are rated to handle 120 psi without failure.
The mover engine, set in the center of the line, is little more than an overgrown lawnmower motor that turns a chain not unlike a bicycle's. The standard mover engine has 7 horsepower, but for a 5' line, an 8 horsepower mover might be needed.
Sprinkler lines need to be staked to the ground when they are not being used as they are relatively light weight and tend to catch random gusts of wind which will cause them to speed across open fields and over short fences until they hit something. As the lines are thin aluminium, hitting something unmovable (e.g. a parked back-hoe) or something traveling at high speed (e.g. a semi-truck on the freeway) will usually cause them to wrap around whatever they hit and be rendered useless.