Operation
A high-torque, insulated electric motor, usually rated at 250–750 watts (⅓ to 1 horsepower) for a domestic unit, spins a circular turntable mounted horizontally above it. Induction motors rotate at 1,400–1,800 RPM and have low starting torque; commutator motors rotate at higher speeds (about 2,800 rpm), have high starting torque, and are usually lighter. However commutator motors are noisier than induction motors, partially due to the higher speeds and partially because the commutator brushes rub on the slotted armature. The higher starting torque of those appliances with a permanent magnet motor ensures in most cases that there will be no blockage.
The added weight and size of induction motors might be of concern. Many models have some degree of sound insulation.
The turntable is surrounded by a shredder ring, which has sharp slots. The food waste sits on the turntable and through centrifugal force is forced to its perimeter and through the shredder ring. The turntable has a number of swiveling lugs—similar to little hammers attached to its topside—which assist in forcing the waste through the shredder. Except for special models, most of the food waste disposers do not have any sharp blades or scissors.
Waste is fed into a chamber above the turntable and drops on the turntable. The chamber may have a rubber partial closure through which waste can be pushed without letting cutlery and other objects fall in, but essentially the chamber is open at the top, and there is access to the turntable. This is useful in the case of a jam: The turntable can be forced round by pushing with a wooden spoon handle or similar object until the jam clears. Waste that cannot be ground successfully can be removed manually.
Most units are of the continuous-feed type, allowing waste to be added as the unit runs. Batch-feed models are also available with a lid that must be locked before operation, making it impossible to run the machine when a user is trying to clear a jam by hand and preventing cutlery, etc. from falling in.
Some commercial and high-end domestic disposals also have an undercutter blade that revolves below the turntable and chops the ground waste, including fibrous material which could cause a drain clog, more finely. These disposals can handle fibrous waste such as artichoke leaves that cannot be successfully ground in a standard disposal.
Waste disposal units may jam but can usually be cleared either by forcing the turntable round from above or by turning the motor using a hex-key wrench inserted into the motor shaft from below. Very hard objects accidentally or deliberately introduced, such as metal cutlery, can damage the waste disposal unit and become damaged themselves. More problematic are drain blockages caused by shredded waste that is fibrous (artichoke leaves) or starchy (potato peelings).
Some higher-end units have automatic reversing. By using a slightly more-complicated centrifugal starting switch, the split-phase motor rotates in the opposite direction from the previous run each time it is started. This can clear minor jams but is claimed to be unnecessary by some manufacturers: Since the late 1970s most disposal units have swivel impellers which make reversing unnecessary.
Another kind of garbage disposal unit, the HydroMaid, is powered by water pressure rather than electricity, and is manufactured by Hydromaid International. Instead of the turntable and grind ring described above, this alternative design has a water-powered unit with an oscillating piston with blades attached to chop the waste into fine pieces. Because of this cutting action, they can handle fibrous waste. Water-powered units take longer than electric ones for a given amount of waste and need fairly high water pressure to function properly. For a period of time in the mid-late 2000s the HydroMaid virtually disappeared from the commercial marketplace. The manufacturer filed for Chapter 11 bankruptcy in 2007. As of October 2011 however, Hydromaid disposals are available again via several online retailers including Amazon.com.
Read more about this topic: Garbage Disposal Unit
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