Dumbwaiters come in two varieties; manual and electric.
Manual dumbwaiters are hand operated. Using a large "pull rope" that is
joined to form a loop, the operator pulls on one side to drive the machine up and the other
side to go down. Automatic brakes hold the dumbwaiter at floor level when the pull rope is
released. Due to the nature of how this unit operates, hoistway door locking devices are
not utilized on this type of unit.
Electric dumbwaiters are pushbutton operated. Typical control is "Full Call and
Send"; this means that at each landing served by the dumbwaiter there is a bank of
pushbuttons representing each of the landings served. Momentary pressure on a pushbutton
will dispatch the dumbwaiter to that landing where it will stop automatically. A
non-interference timer prevents the dumbwaiter from being called to another floor before
someone has a chance to open the door and remove the contents. An optional "Arrival
Lantern & Gong" will both audibly and visually indicate the arrival of the
dumbwaiter at the landing. If the door is left open and someone tries to call the
dumbwaiter, a demand buzzer will alert those in the area to close the door.
The most common type of machine for dumbwaiters is a winding drum machine. Simply put,
to go up the machine turns a drum scored to accept the cable width and wraps the cable on
the drum; to go down that cable is unwound. (See Diagram)
The other common dumbwaiter machine is a traction machine. The traction machine derives
it's name from the lifting force that comes from the traction between the hoist rope(s)
and the sheave that supports it. (See Diagram)