crane pulley types

Crane Pulley: Types, Safety Requirements and Inspection Guide

Introduction

The pulley — also called a sheave — is a key component of a crane’s hoisting mechanism. It performs two main functions: changing the direction of the wire rope and providing mechanical advantage to reduce the effort needed to lift a load. Pulleys are also widely used as equalizer (balance) pulleys to balance the tension between two wire rope falls.

Knowing the different crane pulley types, their safety requirements, and how to inspect them correctly is essential for safe crane operation, reliable load handling, and compliance with hoisting equipment standards.

What Is a Crane Pulley?

A crane pulley changes the direction of the wire rope and helps reduce the force required to raise a load. It is also commonly used as an equalizer pulley to balance the tension between two wire rope falls, ensuring even load distribution across the rope system.

Crane Pulley Construction and Types

Construction of a Crane Pulley

A crane pulley generally consists of a flanged rim with a rope groove, a web (body), and a hub. The groove profile is formed by an arc-shaped bottom and two inclined side walls, which guides the wire rope smoothly and protects it from damage.

Depending on the manufacturing process, pulleys are classified as:

  • Rolled pulleys
  • Cast pulleys
  • Welded pulleys

Pulleys are usually supported on a fixed shaft. Most use rolling bearings, while slow-speed pulleys and equalizer (balance) pulleys may use plain (sliding) bearings.

Fixed Pulley vs. Movable Pulley

Pulleys are classified by whether the axle moves:

  • Fixed (stationary) pulley: the axle is fixed; it only changes the direction of the wire rope.
  • Movable (traveling) pulley: the axle moves together with the load; it provides mechanical advantage and reduces the required lifting force.fixed pulley block Schematic diagram

Crane Pulley Blocks

A pulley block (sheave block) consists of pulleys, bearings, a pulley guard, and other components. Pulley blocks are also divided into fixed blocks and traveling (movable) blocks.

By Function

  • Mechanical-advantage (force-reduction) block: lifts heavy loads with a smaller driving force — the type most commonly used on cranes.
  • Speed-increase block: used where higher travel speed is required.

By Structure

  • Single-reeving (single-fall) block: most commonly used on jib (boom) cranes.
  • Double-reeving (double-fall) block: most commonly used on bridge (overhead) cranes.

Reeving Ratio (Mechanical Advantage)

The reeving ratio is the mechanical advantage — the force multiplication — of the pulley block:

Reeving ratio = Weight of lifting load ÷ Wire rope tension = Wire rope linear speed ÷ Lifting load speed

From this formula:

  • For a single-reeving block, the ratio equals the number of load-carrying wire rope falls.
  • For a double-reeving block, the ratio equals half the number of load-carrying falls.

Arrangement of the Fixed Pulley Block

The number of pulleys in a fixed block corresponds to the reeving ratio of the hoisting mechanism. Depending on the design, cast or rolled pulleys are used. Common arrangements include:

  • The balance (equalizer) pulley arranged vertically relative to the other pulleys;
  • A wire-rope equalizer frame used in place of the balance pulley;
  • The fixed block arranged inside the fixed-pulley beam;
  • The fixed block partly mounted below the trolley deck, or fully mounted above the trolley deck.

Crane Pulley Safety Requirements

  1. Check that the pulley rotates freely by hand. Observe whether the pulley swings sideways. The groove must be smooth and free of any defects that could damage the wire rope. The pulley must be fitted with a device that prevents the wire rope from jumping out of the groove.
  2. A metal cast pulley shall be discarded (taken out of service) if any of the following conditions occurs:
    • (1) Cracks are present;
    • (2) Non-uniform groove wear reaches 3%;
    • (3) Groove wall thickness is worn by 20% of the original wall thickness;
    • (4) The groove bottom diameter is reduced by 50% of the wire rope diameter due to wear;
    • (5) Any other defects that may damage the wire rope.

Crane Pulley Inspection Points

  1. Crack inspection: cracks are detected by visual inspection. A damaged pulley must never be repaired by welding.
  2. Pulley guard: pay close attention to the pulley guard during inspection. The guard of the movable pulley must prevent the pulley from coming into contact with people or objects when the hook descends, and must prevent the wire rope from slipping out of the groove.
  3. Fixed pulleys: fixed pulleys are usually mounted in the middle of the trolley frame and are difficult to observe because of the guard above them. Check whether the fixed pulley rotates freely and whether the rim shows any damage.
  4. Running condition and lubrication: check whether the pulley rotates freely, whether there is abnormal noise, whether the lubrication passages are clear, and whether there is any metal dust or dirt. Also check that the grease nipple and the oil grooves of the bearing spacer ring are properly aligned.
  5. Balance (equalizer) pulley: the balance pulley rotates slightly during operation, causing uneven wear of the groove and shaft. For balance pulleys mounted on the trolley frame, which are difficult to inspect, pay special attention to three points:
    • (1) Check the degree of wear of the groove and the pulley shaft;
    • (2) Remove the wire rope from the pulley and check whether the pulley rotates freely;
    • (3) Check that the connection between the pulley shaft and the trolley frame is secure.
  6. Periodic inspection: inspect and lubricate the pulleys at regular intervals.