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CET Elevator study materials
CET Elevator study resources

CET Elevator: Elevator Systems and Components

CET Elevator · Work through your exam, one topic at a time.

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Elevator Systems and Components

What this domain tests

This domain asks you to identify components and explain their function and interaction: traction and hydraulic drive systems, roping arrangements, counterweights, governors and safety gear, buffers, door operators and interlocks, and the safety chain that ties them together.

Core concepts

  • Traction machines: geared or gearless, driving a sheave. In 1:1 roping the car moves at rope speed; in 2:1 roping the rope moves twice as fast as the car and the car travels half the rope distance.
  • Counterweight: balances the car plus roughly 40–50% of rated load, reducing motor torque and improving traction. It is not equal to the car weight alone.
  • Safety devices: the governor trips at approximately 115–125% of rated speed and lifts the safety gear into the guide rails. Buffers absorb energy at the pit: spring buffers for lower speeds, oil buffers above the spring-buffer limit.
  • Doors: hoistway door interlocks and car door/gate contacts are in the safety chain; the car cannot run with them open except in the limited leveling/inspection modes permitted by code.
  • Hydraulics: power unit, pump, valve, jack, and rupture valve; a relief valve limits pressure and a rupture valve stops uncontrolled descent if a pipe or fitting fails.

Worked example

A car weighs 3,500 lb and has a 2,500 lb capacity. Balance is 45%. Counterweight = 3,500 + (0.45 × 2,500) = 3,500 + 1,125 = 4,625 lb. If the mechanic mistakenly sizes the counterweight as car weight plus full capacity, the machine is over-counterbalanced, traction suffers, and the empty car may not level properly. Reasoning from the balance percentage prevents that error.

Traps that cost marks

  • Mixing up 1:1 and 2:1 roping when calculating car speed or sheave speed.
  • Assuming counterweight equals car weight.
  • Placing safety gear on the counterweight in every design; counterweight safeties are needed only in certain configurations.
  • Forgetting that door interlocks are part of the electrical safety chain, not just hardware.

Component relationships

Learn the chain, not isolated parts: governor trips → safety gear grips rails → car stops; door lock opens → safety chain opens → drive is disabled. Questions frequently test which component acts first.