This nozzlelike emitter is designed to reduce water pressure by causing the water to move along an elongated helical path. With low pressure, the emission hole can by larger, so that its tendency to become clogged is diminished. An emitter of this design is preset at the factory to emit 1, 1.5, or 2 gallons of water per hour. The hook at the right attaches the emitter to the drop-irrigation pipe at a right angle; water enters the conical tip from the center of the pipe. From K. Shoji, "Drip Irrigation." Copyright 1977 by Scientific American, Inc. All rights reserved.