Lifts And Escalators

Understanding the distinction between traction and hydraulic propulsion is fundamental for any maintenance engineer. Traction lifts utilize steel hoist ropes or coated steel belts looped over a drive sheave.

The friction between the ropes and the sheave grooves gives the needed force to move the car and counterweight.

Hydraulic lifts run on the principle of fluid displacement. An electric pump forces hydraulic oil into a cylinder, which extends a piston to raise the car.

These systems are usually restricted to low-rise buildings due to the limitations of piston length and the energy needed to fight gravity without a counterweight.

Traction System Components

Safety and UK rules

Governor: A mechanical overspeed detection device that triggers the safety gear if the car exceeds rated velocity. Variable Voltage Variable Frequency (VVVF) Drive: Regulates motor speed and torque for smooth acceleration and deceleration. Counterweight: Balances the mass of the car plus about 40-50% of the rated load to reduce energy use. Guide Rails: T-shaped steel tracks that maintain the car's path and give the surface for safety gear contact.

Hydraulic System Architecture

The uptime of a hydraulic lift depends on the integrity of the seals and the stability of the fluid temperature. Viscosity changes in the oil can lead to "levelling" issues.

Here, the car fails to align perfectly with the floor. You must monitor hydraulic pressure via calibrated gauges during full-load tests to make sure the relief valve is set correctly.

Feature: Maximum Travel; Traction (MRL/Geared): Unlimited (Building height dependent). Hydraulic: Usually up to 18 metres. Feature: Speed Range; Traction (MRL/Geared): 0.5 m/s to 20+ m/s; Hydraulic: Maximum 0.63 m/s.

Costs and timescales

Feature: Fitting Cost; Traction (MRL/Geared): Higher first capital spend. Hydraulic: Lower first cost for low-rise.

Escalators represent a different engineering challenge. It focuses on continuous motion and synchronized handrail speeds. The drive station, usually located at the upper landing, houses the motor, gearbox, and main drive shaft.

Power is transmitted to the step chains. This pull the steps along a dedicated track system.

What it involves

Safety in escalators is managed by an array of sensors. The "comb-plate" impact switch, for instance, halts the motor if an object becomes lodged between the moving steps and the stationary landing.

You must make sure the gap between the steps and the skirt panels does not exceed 4mm to prevent entrapment.

Critical Escalator Sub-systems

Step Chain: The primary link between the drive and the steps.

Needs precise tensioning to prevent "hunting" or jerky motion. Handrail Drive: Friction-driven wheels that must be synchronized with the step speed within a 0% to +2% tolerance. Braking System: Includes both a working brake for normal stops and an emergency brake for overspeed or reversal detection. Lubrication System: Automated oilers that deliver metered doses to the chain rollers and guides.

In the United Kingdom, the upkeep of lifts and escalators is strictly governed by the Health and Safety Executive (HSE).

The Lifting Operations and Lifting Equipment Regulations 1998 (LOLER) need that all lifting equipment is "thoroughly examined" by a competent person.

Safety and UK rules

This is distinct from routine maintenance and acts as a forensic audit of the equipment's safety status.

The Safety Assessment Federation (SAFed) gives the technical guidelines (LG1) for these examinations. As a technician, you must document all findings in a formal report. Any "Category A" defects—those posing an immediate danger.

What to check and report

Need the equipment to be removed from service at once until the fault is rectified.

Examination Frequencies

Costs and timescales

Passenger Lifts: Every 6 months. Goods-only Lifts: Every 12 months. Escalators and Moving Walks: Every 6 months (due to high public interface). New Fittings: Before being put into service for the first time.

Modern equipment relies on microprocessor-based controllers that communicate via CAN bus or similar protocols.

When troubleshooting, your first action should be to interface with the controller using the appropriate diagnostic tool to extract the error log. This log gives a timestamped sequence of events leading to the fault.

Safety and UK rules

Common fault codes often relate to door interlock circuits. The safety string—a series of switches connected in electrical series—must be complete for the lift to move. If any contact in the string, such as:

• The pit emergency stop or the car top inspection switch
• Is open
• The controller will inhibit the drive

Step-by-Step Fault Isolation

What to check and report

1. Check Power Supply: Check all three phases at the main isolator.

Make sure the voltage is within +/- 10% of the nominal rating.
2. Inspect Safety Circuit: Use a multimeter to check for continuity through the safety string.

Do not use short-term jumpers except for diagnostic purposes under controlled conditions.
3. Check Encoder Feedback: For traction units. Make sure the motor encoder is giving a clean signal.

A faulty encoder can cause erratic movement or "roll-back" during start.
4. Evaluate Brake Operation: Confirm the brake plungers are firing and the linings have enough thickness.

Adjust the microswitches if they fail to signal the controller that the brake has lifted.

Legacy lifts and escalators often suffer from component old age. Upgrade work involves replacing the control system, drive, and signal fixtures while retaining the building elements like guide rails and car frames.

This approach improves uptime and reduces energy use by up to 40% through the use of regenerative drives.

Regenerative drives capture the energy generated when a heavily loaded car travels down (or an empty car travels up) and feed it back into the building's electrical grid.

In busy settings, this gives a big return on investment. You must make sure that the building's electrical infrastructure can handle the harmonic distortion sometimes linked with these drives.

Hydraulic System Refit

When servicing hydraulic units, pay close attention to the valve block. Modern electronic valves offer much better levelling accuracy and ride quality than older mechanical versions.

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Replacing a standard motor starter with a "Soft Starter" can also reduce the high inrush current that stresses the pump motor and building power supply.

Safety is the primary engineering constraint for all vertical transport. The safety gear, a mechanical brake mounted on the car frame.

Is designed to clamp onto the guide rails if the hoist ropes fail or the car overspeeds. This is a "fail-safe" mechanism that runs independently of the control system.

For escalators, the emergency stop buttons must be clearly marked and functional at both landings. The "skirt deflectors" (brushes) are not merely aesthetic.

What it involves

They are designed to keep passenger footwear away from the gap between the moving step and the stationary side panel, reducing the risk of friction-based entrapment.

Emergency Release Operations

If there is a passenger entrapment, only trained personnel should do a manual release.

For traction lifts, this involve releasing the brake manually while controlling the speed of the car using the handwheel (on geared machines) or the electrical manual move buttons (on gearless MRL machines).

You must always confirm the car's position relative to the floor levels before opening the doors.

In settings such as construction sites or heavy manufacturing plants, specialist equipment like scissor lifts and boom lifts are employed.

These follow similar hydraulic and electrical principles but are subject to different environmental stresses, such as dust, moisture, and extreme temperatures.

Technicians working on these systems must be familiar with load-sensing tech. Many modern aerial work platforms use strain gauges to prevent operation if the platform is overloaded.

Calibrating these sensors needs certified test weights and a deep understanding of the machine's load-moment characteristics.

Mechanical wear is inevitable in high-cycle equipment. For lifts and escalators, the primary wear points are the rollers, bearings, and ropes. Steel wire ropes must be inspected for "crowning".

Broken wires on the outer strands—and rouge (oxidisation). If the rope diameter has decreased by more than 6-10% (depending on manufacturer specs), replacement is required.

What it involves

Escalator steps are prone to wear. Periodic non-destructive testing (NDT) of step axles and wheels is recommended in busy transit hubs.

If a step wheel develops a "flat spot," it will create a rhythmic thumping noise and increased vibration, which can eventually damage the tracks.

Vibration and Acoustic Checking

Implementing a predictive maintenance strategy involves the use of accelerometers to measure vibration signatures.

Costs and timescales

By comparing the current signature against a "healthy" baseline, you can predict the failure of a main drive bearing or a gearbox months before it occurs.

This minimizes unplanned downtime and allows for planned repairs.

The carbon footprint of lifts is a growing concern for facility managers. Beyond regenerative drives, LED lighting in car interiors and "standby modes" for controllers can a lot reduce passive energy draw.

For escalators, "sleep modes" utilize sensors to slow the motor to a crawl when no passengers are detected, accelerating to full speed only when a user approaches.

Lubrication also plays a role in sustainability. Using biodegradable synthetic oils in hydraulic systems reduces the environmental impact of potential leaks.

Also, high-efficiency lubricants in escalator chains reduce friction, thereby lowering the amperage needed to drive the motor under load.