Traction Elevators

Traction Elevator Basics

Traction elevators are suspended from cables. The reason that they’re called traction elevators is because the traction between the cable and the sheave allows the car to move up and down with the motion created by the motor. The cables are called ropes and for a very good reason. Originally some elevators were installed with manila ropes. There are a very few still around today. Today’s steel cables actually have rope material inside of them to carry lubricants to the cable to minimize wear.  The wear comes in when the rope moves up and down over the sheave (pulley). It twists as it changes direction and the strands in the cable rub against one another.  Almost all traction elevators are elevators are suspended by more than one rope for safety purposes. Each individual rope is capable of holding a fully loaded car. If all of those fail the governor rope is employed to suspend the car. On average each elevator has three to five ropes attached.  One end is attached to the cab while the other end is attached to a set of counterweights to balance the load. Note: Drum type machines do not have counterweights and the cable is wound onto a drum, sort of like your fishing reel. There are a few of these still in use but they are no longer manufactured in the US. Traction machines are either installed on the roof or in the basement.  Most of them have 1 to 1 roping configurations meaning that with the cable draped over the pulley the counterweights are on one side and the car is on the other.  For every turn of the drive sheave the elevator will travel the circumference of the sheave.  In a 2 to 1 configuration the ropes go under the car and the elevator is suspended on a loop in the ropes. Thus for every two turns of the drive sheave the elevator only travels the distance of one turn.  This reduces loads on the motor and enables smaller faster motors to be used. 

Traction elevators are either geared or gearless, that is they either work on a system of gears to provide power to the sheaves or in the case of gearless work directly off the motor.  Geared elevators are limited in hoistway speeds therefore are mostly used in low to mid rise buildings. The machine in a geared elevator consists of a worm and ring gear that reduces the motor speed to convert it to the power required to lift the car.  In this configuration smaller motors are used to reduce cost and power requirements. High rise buildings require faster speeds.  The sheave is actually part of the motor with no reduction gears. The motors are larger to provide the horsepower needed.  

Earlier models were built with almost all direct current motors.  The direct current allows greater control of the motor to be able to slow down gradually when coming in to a floor so as not to bypass it. Inversely they are also able to start slow and ramp up speed to avoid starting with a jolt.  Two speed AC motors were used in some installations. They worked but not really all that well. Any of you that have been to Europe and ridden some of the older elevators may have experienced a ride in an AC unit.  When the elevator stops you feel like you have just landed on a bowl of jello with a boinnnng type of effect. It’s only due to recent technology that we have been able to control AC to such a degree that the elevator will stop and start accurately every time.

Main components of traction elevators consist of:

1.       A main control device that turns the power on and off to the motor.

2.       A motor (of course)

3.       Cables that hook up to a counterweight system

4.       A passenger car

5.       Sensing devices that signal the controller

6.       A device that controls power to an AC motor or a device that generates DC power to a DC motor

Many people think that Elija Otis invented the elevator. All that Otis did was develop a safety brake that enabled humans to ride in elevators safely.

In the next posting we can go into some of the common items found on both major types of elevators. As always, please don’t hesitate to contact me with any questions or comments that you may have. I will make your questions the subject of future publications to make sure that everyone is fully informed.  Send your questions/comments to elevatorernie@hotmail.com. I am looking forward to hearing from you.

Quote of the day: “You have to stay in shape. My grandmother, she started walking five miles a day when she was 60. She's 97 today and we don't know where the hell she is.”

- Ellen DeGeneres

Elevator Basics

There are several different types of elevators in use today the main ones being traction elevators and hydraulic elevators. At this time I think it’s best that we stay with the main ones until we get further along in the blog. Talking about roped hydros, screw drive units, telescopic chain driven, and such at this point serves only to confuse the reader so at this point we are discussing only two major types.  So our first publication will cover the basics of…..

Hydraulic Elevators

Hydraulic elevators, or hydro’s are by far the most common elevators found. They are the least expensive to install and maintain and not really that much more expensive to operate. Today most elevator companies allow two weeks for the construction of an average hydraulic elevator. In the past almost all elevators were custom built however today due to time and cost pressures they come in kits. Some companies even provide pre-assembled units built at the factory. All that you have to do is have the pit constructed and set the prebuilt elevator shaft and car onto it, hook up the controls and away you go. For reasons that we can discuss later most elevator experts feel that this is not always the best way to go.

Hydraulic Basics

I think it’s best to start with hydros’ The easiest way to visualize the inner workings of a hydraulic elevator is to recall your younger days when you went to the auto repair shop with your Dad and watched the mechanic raise the car on a lift. The lift is a hydraulic elevator of sorts and has many of the basic parts. The big silver tube that rises out of the ground is the ram or piston.  Hydraulic fluid is pumped into the cylinder buried underground at high pressure. The piston rises in the cylinder to make room for the oil that’s being pumped in.  When the piston reaches its’ maximum stroke height the mechanic engages a locking device to ensure that a loss of oil pressure doesn’t turn him or her into an oil spot on the floor and they can then safely work under the car. When they are finished they disengage the locking device and the hydraulic oil is returned to a holding tank driven only by the weight of the vehicle on the platform.  An inground hydraulic elevator is much the same however it has many sophisticated devices added to ensure safety for the riding public.

Generally hydros consist of the following components:

A power unit

Hydraulic jack

Passenger car

Controlling device

Most passenger, freight, and service hydros use either a dry type or submersible power unit. A dry type has the motor, pump, and valve mounted outside of the oil storage tank, usually underneath.

Submersible units have the motor mounted under the oil level. This provides some cooling to the motor and mounting the pump and valve in the tank saves space. Submersible units not only save space they use less hydraulic oil. This can lessen the impact of an oil spill in the event of a ruptured oil line and also costs less to fill.  Problems with submersible units occur if they are used too frequently. There isn’t enough oil in the system to dissipate all of the heat that is generated from use and the heat can degrade the components of the system thereby contaminating the oil and degrading it’s insulating value in the motor and lessening the heat dissipation value further.  Submersible units are great space savers and are an excellent solution where the use of the elevator is not constant.  As an aside I remember seeing a submersible unit that was used in an extremely high traffic area that ran at a constant 160 degrees Farenheit. In a three year period it went through three motors. Another was at a mall that ran constantly at least 12 hours per day. The one at the mall had broken down the oil and it had turned black. Shortly thereafter the motor failed causing great stress to all involved.

Dry type power units have a greater quantity of oil and since the motor is air cooled the oil only generates heat from the friction of being forced back and forth through the system. Dry types cost more and they take up more space causing submersible units to be used whenever possible.

Hydraulic elevators operate on several different fluids. The first ones to be built over a century ago used city water. That was quickly eliminated by using hydraulic oil whis was and still is a staple in the industry. Recently companies have been developing more environmentally friendly fluids. In some cases vegetable oil is used. One of the characteristics of vegetable oil is the odd smells generated. I have heard of some smelling like French fries but mostly just an odor like leaking natural gas. Another downside of these products is that they don’t perform as well as standard hydraulic oil. Standard hydraulic oil maintains its’ viscosity through a wide variety of temperature ranges. That keeps things like leveling constant throughout the day such as first thing in the morning when your elevator is cold to the rush hour at 5PM when the temperature of the fluid is hot. Viscosity plays an important part in how a hydraulic elevator levels. As the viscosity changes so will the leveling characteristics of an elevator. It either stops too late or too soon causing the car to miss landing exactly at the sill. This causes a tripping hazard and opening up the owner for an injury lawsuit.

The movement of fluid in the system is governed by a main control valve.  There are several versions of main valves but most of them operate with a series of valves to regulate the speed of the fluid flow. Many of today’s main control valves contain at least four internal valves within the housing. There are two dedicated to each direction a small and a large. In the up direction the small valve starts the elevator moving slowly so as not to provide too much of a jolt to the passengers and also to lessen the starting load on the pump and motor. When a reasonable speed is reached the large valve opens and the elevator proceeds to full speed smoothly. This speed change is known as “transition”. In hydraulic elevators it is governed by distance, that is the large valve receives a signal to open after the car has passed a sensor that is carefully positioned in the hoistway. When the elevator gets ready to slow down the car passed a sensor in the hoistway that tells the large valve to close. This effectively slows down the elevator allowing it to “creep” in to the floor at a slow speed. When it reaches the sensor signals the arrival at the floor the valve closes and the system stops. The slow speed keeps the car from overshooting the floor and it should be level at that point.  Because there is a minute delay in the transferring of signals to the controller and then out to the main control valve and motor the sensors must be placed slightly ahead of the movement modification points.  This is done by a trial and error method performed by the setup technician.  A change in viscosity can cause a change in speed characteristics therefore causing an error in leveling at the floor. In the down direction the internal valves operate the same way except the motor and pump are not activated.  Directional sets are used due to control direction of flow, differential pressures involved, and ease of adjustment in directional travel among other more technical reasons.

My next edition will discuss basics of an overhead traction elevator. After that we can get into safety devices for each type of elevator followed devices common to all types then on to specifics.

Please don’t hesitate to contact me with any questions or comments that you may have. I will make your questions the subject of future publications to make sure that everyone is fully informed.  Send your questions/comments to elevatorernie@hotmail.com. I am looking forward to hearing from you.

Quotation of the Month:  "An appeaser is one who feeds a crocodile—hoping it will eat him last."

Winston Churchill

Elevators for Dummies

A Basic Understanding of Elevators

This weblog is being written to inform the average property manager, plant engineer, maintenance engineer or anyone else who may be interested about types of elevators, how they work, pitfalls, limitations and just about anything else that you may want to know about them. After having spent thirteen years in the industry, I still don’t know everything but I know two people in the industry who do.

There are several different types of elevators in use today the main ones being traction elevators and hydraulic elevators. At this time I think it’s best that we stay with the main ones until we get further along in the blog. Talking about roped hydros, screw drive units, telescopic chain driven, and such at this point serves only to confuse the reader so at this point we are discussing only two major types.  So my first publication will cover the basics of…..

Hydraulic Elevators

Hydraulic elevators, or hydro’s are by far the most common elevators found. They are the least expensive to install and maintain and not really that much more expensive to operate. Today most elevator companies allow two weeks for the construction of an average hydraulic elevator. In the past almost all elevators were custom built however today due to time and cost pressures they come in kits. Some companies even provide pre-assembled units built at the factory. All that you have to do is have the pit constructed and set the prebuilt elevator shaft and car onto it, hook up the controls and away you go. For reasons that I can discuss later most elevator experts feel that this is not always the best way to go.

Hydraulic Basics

I think it’s best to start with hydros’ The easiest way to visualize the inner workings of a hydraulic elevator is to recall your younger days when you went to the auto repair shop with your Dad and watched the mechanic raise the car on a lift. The lift is a hydraulic elevator of sorts and has many of the basic parts. The big silver tube that rises out of the ground is the ram or piston.  Hydraulic fluid is pumped into the cylinder buried underground at high pressure. The piston rises in the cylinder to make room for the oil that’s being pumped in.  When the piston reaches its’ maximum stroke height the mechanic engages a locking device to ensure that a loss of oil pressure doesn’t turn him or her into an oil spot on the floor and they can then safely work under the car. When they are finished they disengage the locking device and the hydraulic oil is returned to a holding tank driven only by the weight of the vehicle on the platform.  An inground hydraulic elevator is much the same however it has many sophisticated devices added to ensure safety for the riding public.

Generally hydros consist of the following components:

A power unit

Hydraulic jack

Passenger car

Controlling device

Most passenger, freight, and service hydros use either a dry type or submersible power unit. A dry type has the motor, pump, and valve mounted outside of the oil storage tank, usually underneath.

Submersible units have the motor mounted under the oil level. This provides some cooling to the motor and mounting the pump and valve in the tank saves space. Submersible units not only save space they use less hydraulic oil. This can lessen the impact of an oil spill in the event of a ruptured oil line and also costs less to fill.  Problems with submersible units occur if they are used too frequently. There isn’t enough oil in the system to dissipate all of the heat that is generated from use and the heat can degrade the components of the system thereby contaminating the oil and degrading it’s insulating value in the motor and lessening the heat dissipation value further.  Submersible units are great space savers and are an excellent solution where the use of the elevator is not constant.  As an aside I remember seeing a submersible unit that was used in an extremely high traffic area that ran at a constant 160 degrees Farenheit. In a three year period it went through three motors. Another was at a mall that ran constantly at least 12 hours per day. The one at the mall had broken down the oil and it had turned black. Shortly thereafter the motor failed causing great stress to all involved.

Dry type power units have a greater quantity of oil and since the motor is air cooled the oil only generates heat from the friction of being forced back and forth through the system. Dry types cost more and they take up more space causing submersible units to be used whenever possible.

Hydraulic elevators operate on several different fluids. The first ones to be built over a century ago used city water. That was quickly eliminated by using hydraulic oil whis was and still is a staple in the industry. Recently companies have been developing more environmentally friendly fluids. In some cases vegetable oil is used. One of the characteristics of vegetable oil is the odd smells generated. I have heard of some smelling like French fries but mostly just an odor like leaking natural gas. Another downside of these products is that they don’t perform as well as standard hydraulic oil. Standard hydraulic oil maintains its’ viscosity through a wide variety of temperature ranges. That keeps things like leveling constant throughout the day such as first thing in the morning when your elevator is cold to the rush hour at 5PM when the temperature of the fluid is hot. Viscosity plays an important part in how a hydraulic elevator levels. As the viscosity changes so will the leveling characteristics of an elevator. It either stops too late or too soon causing the car to miss landing exactly at the sill. This causes a tripping hazard and opening up the owner for an injury lawsuit.

The movement of fluid in the system is governed by a main control valve.  There are several versions of main valves but most of them operate with a series of valves to regulate the speed of the fluid flow. Many of today’s main control valves contain at least four internal valves within the housing. There are two dedicated to each direction a small and a large. In the up direction the small valve starts the elevator moving slowly so as not to provide too much of a jolt to the passengers and also to lessen the starting load on the pump and motor. When a reasonable speed is reached the large valve opens and the elevator proceeds to full speed smoothly. This speed change is known as “transition”. In hydraulic elevators it is governed by distance, that is the large valve receives a signal to open after the car has passed a sensor that is carefully positioned in the hoistway. When the elevator gets ready to slow down the car passed a sensor in the hoistway that tells the large valve to close. This effectively slows down the elevator allowing it to “creep” in to the floor at a slow speed. When it reaches the sensor signals the arrival at the floor the valve closes and the system stops. The slow speed keeps the car from overshooting the floor and it should be level at that point.  Because there is a minute delay in the transferring of signals to the controller and then out to the main control valve and motor the sensors must be placed slightly ahead of the movement modification points.  This is done by a trial and error method performed by the setup technician.  A change in viscosity can cause a change in speed characteristics therefore causing an error in leveling at the floor. In the down direction the internal valves operate the same way except the motor and pump are not activated.  Directional sets are used due to control direction of flow, differential pressures involved, and ease of adjustment in directional travel among other more technical reasons.

My next edition will discuss basics of an overhead traction elevator. After that we can get into safety devices for each type of elevator followed devices common to all types then on to specifics.

Please don’t hesitate to contact me with any questions or comments that you may have. I will make your questions the subject of future publications to make sure that everyone is fully informed.  Send your questions/comments to elevatorernie@hotmail.com. I am looking forward to hearing from you.

Quotation of the Month-- "An appeaser is one who feeds a crocodile—hoping it will eat him last." ---Winston Churchill