SERVICES – Installation – DumbwaitersDumbwaiters, Elevators and Vertical Reciprocating Conveyors 
Dumbwaiters come in two varieties; manual and electric. Dumbwaiters are not elevators nor are they Vertical Reciprocating Conveyors (VRCs). Elevators, including freight elevators, are permitted to carry passengers; dumbwaiters and VRCs are not permitted to carry passengers. Dumbwaiters and elevators are subject to ANSI A17.1 – the national Elevator Safety Code. Vertical Reciprocating Conveyors are subject to ANSI B20.1. The maximum size for a dumbwaiter, per ANSI A17.1, is 36" x 36" x 48" and the maximum rated load (capacity) is 500 pounds. Elevators and VRCs do not have a code specified maximum rated load. Manual Dumbwaiters Manual dumbwaiters are hand operated. Using a large "pull rope" that is joined to form a continuous 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. Also due to the nature of the operation of this type of device, the maximum load it can carry is limited. Electric Dumbwaiters Electric dumbwaiters are typically driven by either winding drum machines, chain drive machines or traction machines. The machines are typically located inside the hoistway, either above the top landing or below the bottom landing, but they can be located outside the hoistway in a dedicated machine space. In very rare circumstances, dumbwaiters are driven by hydraulic machines. The maximum amount of weight a dumbwaiter may carry, it’s "rated load", may not exceed 500 pounds. The maximum clear inside height of a dumbwaiter may not exceed 48 inches and the platform may not exceed 10.75 square feet. It is permissible to have shelves in a dumbwaiter. Control of an electric dumbwaiter is normally done through a set of call buttons at each landing; one button for each landing served. This is referred to as "Full Call and Send". 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 its name from the lifting force that comes from the traction (or friction) between the hoist rope(s) and the sheave that supports it. (See Diagram) Diagram for Roped Hydro. |
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