Based on the method of connection between the elevator car and the hydraulic cylinder, hydraulic elevators can be classified into two types: direct-acting and indirect-acting.
1) Direct-acting systems involve a plunger acting directly upon the elevator car or its car frame. The connection between the car and the plunger must be flexible. Direct-acting hydraulic elevators do not require an emergency safety braking device or a speed governor; consequently, the car structure is simpler, and the hoistway space required is minimal. Furthermore, there is no need for hoisting ropes or cables at the top of the building; since the entire load of the car is transmitted to the bottom of the pit, a relatively deep vertical bore must be excavated to accommodate the hydraulic cylinder.
2) Indirect-acting systems connect the plunger to the car frame via a suspension mechanism (typically ropes or chains). Generally, the displacement ratio between the plunger and the elevator car is 1:2, although ratios of 1:4 and 1:6 are also utilized. Indirect-acting hydraulic elevators do not require a deep vertical bore; however, because they employ ropes or chains, they must be equipped with a speed governor and safety gear mechanisms. Since the lifting hydraulic cylinder is positioned to the side of the elevator car, the hoistway space required is somewhat larger than that of the direct-acting type.
