Handrails and handrail drives

The call from the transit station came in at four in the afternoon: the street entrance up escalator had stopped itself twice during the lunch hour, and the station attendant had restarted it both times with the key. The controller's fault log, which Tamsin read on the service tool when she and Nell arrived, showed the same fault both times: left handrail speed low. Outside, the morning's rain had turned to a cold drizzle, and the left handrail, which faces the street, was wet. "Handrails are the part passengers hold onto, and they are the part that slips first," Nell said. "If the steps go on and the handrail lags, people get pulled backward. So the controller watches it, and so do we." This lesson covers handrails, the drives that move them, the guides they run in, and the devices that watch their speed and guard the places where they enter the balustrade.

What a handrail is made of

An escalator handrail is a continuous loop of molded rubber or thermoplastic, roughly C-shaped in section, that slides around a guide on top of the balustrade. Inside it are layers that give it strength and let it slide: a set of steel wires or a steel band that carries the tension and keeps the handrail from stretching, fabric plies that hold its shape, and a low-friction slider fabric on the inside surface that runs on the guide. The outer cover is the part passengers touch, and it must be smooth, unbroken and clean. A handrail is made to the exact length of its loop and joined on site by vulcanizing or by a molded splice, so a new handrail is a planned job with special equipment rather than a quick repair. Transit guidelines ask for steel tension members strong enough to carry a large load across the splice.

The handrail runs along the top of the balustrade on the passenger side, turns around the newel at each end, and returns inside the balustrade or under the truss, where the drive and the tensioning devices are. The code sets the height of the handrail above the step noses, between 35 in and 39 in, the clearance between the handrail and anything beside it, and how far the handrail must extend beyond the comb at each landing, at least 12 in, so that a passenger still has something to hold while stepping off.

Handrail drives

The handrail must move in the same direction as the steps and at substantially the same speed. On most escalators it is driven from the main drive shaft, through a chain to a handrail drive shaft, so that it can never run without the steps. Two kinds of drive are common. A sheave or wheel drive wraps the handrail around a large drive wheel near the upper newel, with a pressure belt or rollers holding it against the wheel. A linear or friction drive grips a straight section of the handrail between a driven belt or a row of driven rollers and a row of pressure rollers, pushing the handrail along. Linear drives are gentler on the handrail because they do not bend it around a tight radius, and many modern units use them.

Every drive works by friction, so it depends on the pressure between the handrail and the drive surface and on the condition of both. Worn drive rollers, glazed or contaminated drive belts, pressure rollers out of adjustment, a handrail that has stretched or swollen, and water, oil or ice on the handrail all reduce the grip. When the grip is not enough, the handrail slips: it runs slower than the steps, and under a heavy passenger load it can almost stop. Passengers holding a slipping handrail are pulled backward relative to their feet, which is why handrail slip is a safety problem and not only a comfort complaint.

Handrail speed: the target and the limit

Makers set the handrail to run at the step speed or very slightly faster, so that a passenger's hand is drawn forward rather than backward. The European standard EN 115 states this directly as a tolerance of zero to plus two percent of the step speed, and North American makers use similar settings. A handrail running slightly faster also stays tight on the passenger side of its loop. The code's own requirement is that the handrail moves with the steps, and it backs that up with a handrail speed monitoring device: if the handrail speed differs from the step speed by 15 % or more, the device stops the escalator after a short delay, between 2 and 6 seconds, so that a moment's slip as a crowd grabs the rail does not stop the unit every time. Some controllers also log a warning at a smaller difference, which is how Nell's crew finds a slipping drive before it causes a stop.

# Handrail and step speed check from tachometer readings
step_speed = 98.8                 # measured at the step nose, ft/min
handrails = {"left": 95.7, "right": 99.8}   # measured on the handrail, ft/min
for side, v in handrails.items():
    diff = 100 * (v - step_speed) / step_speed
    if 0 <= diff <= 2:
        verdict = "within the maker's target of 0 to +2 %"
    elif diff <= -15:
        verdict = "at or beyond the 15 % shutdown limit"
    elif diff < 0:
        verdict = "slow: adjust or repair the drive"
    else:
        verdict = "too fast: check the drive setting"
    print(f"{side:>5}: {v} ft/min, {diff:+.1f} % against the steps, {verdict}")

 left: 95.7 ft/min, -3.1 % against the steps, slow: adjust or repair the drive
right: 99.8 ft/min, +1.0 % against the steps, within the maker's target of 0 to +2 %

With no load the left handrail at the station was running about three percent slow, and it was much slower under the lunch-hour crowd, enough to trip the monitor. The right handrail was within the target. Nell's measurements are taken with a hand tachometer and a contact wheel, at the step nose for the steps and on the top of the handrail at the same point; the readings are repeated in both directions and at both ends, because a handrail that stretches can run at different speeds along its length.

Why handrails slip and how they are fixed

At the station, the cause of the slip was a combination that Nell had seen many times on outdoor units. The pressure rollers on the left drive had worn smooth, the drive belt had glazed, and the wet handrail had lost the rest of its grip. The fix was to replace the pressure rollers and the drive belt with the maker's parts, set the roller pressure to the maker's figure, clean the handrail and the drive surfaces with the maker's cleaner, and check the handrail tension. After the work, the left handrail ran at the step speed plus about one percent, and a load test with the station staff leaning on the rail, as a crowd would, showed no slip. Nell added a note to shorten the drive inspection interval on the street entrance units during the wet months.

The opposite fault, a handrail that runs too fast or is too tight, wears the handrail and the drive quickly and makes the handrail run hot at the newels. Tension is set with the take-up device on the return side so that the loop is snug on its guides without dragging; the maker gives the setting, often as a measured sag or a spring length.

Handrail inlets and other guards

Where the handrail turns into the balustrade at each newel, it passes through an inlet, the most dangerous point on the handrail. A child's hand resting on the handrail can be carried into the inlet. The inlet is shaped and fitted with a flexible guard or brush to keep fingers out, and behind it a handrail entry device, a switch, stops the escalator if anything pushes the guard inward. The code also limits how high the handrail enters the balustrade above the floor, so that small children's hands are less likely to reach it. The inlet devices are tested at every maintenance visit by pushing the guard with a test tool until the switch opens, and the escalator must stop.

Above the handrail, the code requires guards where the handrail passes close to a ceiling, a floor edge or a wall, so that a passenger leaning out cannot be trapped between the moving handrail and the building. Deck barricades on wide outer decks stop people, usually children, from climbing onto the deck and sliding. Anti-slide knobs on wide decks between escalators stop people sliding down them. All of these are checked during periodic inspections because building changes, such as a new ceiling, a new shop front or a sign, can create a new trap point after the escalator was approved.

Handrail care on a busy site

Handrails wear at the cover, crack at the edges where they bend around the newels, and lose their gloss and grip. Graffiti, gum and stickers are a constant problem at the transit station. Nell's crew cleans handrails with the maker's cleaner only, because solvents and some building cleaners swell the rubber or attack the slider fabric. Small cover cuts can be repaired, but a handrail with cracks that reach the tension members, a broken steel band or a failing splice is replaced. In cold weather, outdoor handrails stiffen, and some outdoor units have handrail heaters or covers; at the station, the agency's specification for the replacement escalators asks for heated handrails at the street entrance.