Here's an overview of hydraulic elevators from AIA/ARCOM MasterSpec's commentary.
UPDATE: Installations over 2 stories are probably better off with a microcontrolled machine room-less traction elevator or a roped hydraulic elevator. --JD
UPDATE: Installations over 2 stories are probably better off with a microcontrolled machine room-less traction elevator or a roped hydraulic elevator. --JD
HYDRAULIC HOISTING MACHINES
There are several configurations of hydraulic hoisting machines. The simplest hoisting arrangement is a single-stage cylinder positioned under the car. Another configuration uses one or more single-stage or telescoping, multiple-stage cylinders beside the car. A third configuration is the roped hydraulic, consisting of one or more hydraulic jacks beside the car, with steel ropes fed over sheaves on the plunger ends, and attached to the car at one end and to the jack cylinder or pit floor at the other.
In-Ground Cylinders:
The cylinder must be slightly longer than the elevator travel distance and requires a well hole of that depth below the pit floor. Well-hole excavation, which requires using a drill rig, must be done early in the Project when the drill is not constrained by the construction around or above it. If hard rock is encountered during drilling, installing an elevator with an in-ground cylinder may not be as economical as installing an elevator with an aboveground cylinder arrangement. If the well hole is in soft ground, a well casing, which may be temporary, might be needed to prevent the well hole from caving in before the cylinder is installed. In-ground-cylinder installation also requires precautionary measures to ensure that hydraulic oil does not leak from the cylinder and pollute the ground water. Elevator Code provisions minimize this risk and the risk of an elevator descending at an unsafe speed due to leaking oil from a corroded cylinder. See the "Environmental Considerations" Article in these Evaluations for more information on protecting in-ground cylinders from corrosion.
Aboveground Cylinders:
One arrangement, which is limited to two stops (travel distance of one story), uses one or more single-stage cylinders that are placed beside the car and lift the car from the top. If telescoping or multiple-stage cylinders are used instead of single-stage cylinders, three or more stops (travel distance of several stories) can be accommodated. Because multiple-stage cylinders are more complicated and have more moving parts than single-stage cylinders, they are more expensive and require more maintenance. With cylinders placed beside the car, telescoping units are easily installed within existing buildings. When using a single beside-the-car cylinder, the guide-rail system must be able to withstand additional loads due to the eccentric arrangement. Note that elevators with aboveground cylinders still require pits.
Roped hydraulic systems consist of one or more hydraulic jacks, located beside the elevator within the shaft, with steel ropes fed over sheaves on the plunger ends and attached to the car at one end and to the jack cylinder or pit floor at the other. Because of the roping arrangement, the car travels twice as far as the plunger; therefore, the jack length, when extended, is only slightly more than the elevator travel and easily fits within the shaft. In Europe, additional sheaves are used to obtain higher roping ratios, but the Elevator Code limits the roping ratio to 2:1 in the United States and Canada. Because the car is suspended from ropes, roped hydraulic units are required to have braking devices (safeties) that grab the guide rails if the equipment fails. Roped hydraulic units are usually more expensive than direct single-stage units because they are more complicated than direct cylinders and have more moving parts. Note that roped hydraulic elevators also require pits.
Hydraulic pumps can be mounted either on the oil tank, using the tank as an inertia block to dampen vibrations and noise, or submerged within the tank, where the oil also absorbs some of the vibration and noise. For some manufacturers and certain elevator sizes, submersible pumps are standard; for others, they cost extra and may be unavailable for some sizes. Consult elevator manufacturers about cost and availability before specifying either pump arrangement. If submersible pumps are not used, use additional sound-absorbing material. Also, consider the machine room location in the building: It should not be too remote, usually no more than 20 feet (6 m) from the hoistway, but should not be located next to spaces where the pump noise would create problems.
Hydraulic elevator motors have traditionally been standard single-speed ac motors because valving arrangements can be used to vary the elevator speed for smooth starting and leveling in both the up and down directions. Reduced-voltage starting arrangements are used to minimize strain on the building's electrical system. Variable-voltage, variable-frequency (VVVF) control can also be used to minimize strain on the building's electrical system and to control the pump speed for smoother starts in the up direction. VVVF control also increases energy efficiency. See the Evaluations in Section 262419 "Motor-Control Centers" for additional information on motor-starting arrangements.
Structural Requirements:
Hydraulic elevator installations do not usually transfer large structural loads to the building frame. Only the small lateral loads from guide rails are imposed, and these result primarily from eccentric loading in cars. This consideration may be important if elevators are being added to an existing building. Hydraulic elevators impose a load on the pit floor, which must be adequately reinforced to receive that load.
