Elevator Car Leveling

Elevator Leveling

Elevator leveling really doesn’t sound like much but it can be a huge issue for you the owner/property manager. A passenger who trips due to an offset elevator can be injured and sue the owner, the service company and just about anyone else in the neighborhood. Many elevator service companies negotiate their way out of the lawsuits with settlements that keep the costs lower than if they went to court.

Through the years many different schemes have been used to get an elevator car to stop evenly with the floor that it’s on.  Prior to 1950 we had elevator operators.  They actually “drove” the elevators. They had a handle to accelerate, slow down, and stop.  When you entered an elevator it was their responsibility to keep you away from the door, and then when the door was closed, release the brake, start the elevator in either the up or down direction, take you to your desired floor, slow it down, and finally bring it to a stop level with the floor.  Although it must have been a boring job it did take some skill to keep from undershooting and overshooting the floors. Of course if it wasn’t perfectly level the operator would caution you to watch your step when leaving the elevator.  All of that changed with the introduction of automatic service in the 40’s.

To begin the understanding of elevator leveling you have to know that each elevator is set up with a “profile” of how it’s supposed to run. When you push the button the door closes and the elevator is ready to start in either the up or down direction. The car starts to accelerate at a slow speed to avoid jolting the passengers. Think of it as a car taking off from a stoplight. If the driver floors it immediately you get pinned to the seat. Instead the driver will gradually pick up speed until he can shift to the gear that will take the vehicle to top speed. Elevators work the same way. The distance covered between the start and the shift to full speed is called the transition zone. They also employ transition zones in the slow down phase too, as sudden stops aren’t welcomed by most passengers.

Many elevators employ a system of mechanical switches in the shaft used to slow down then stop the elevator. The positions of the switches define the transition zones.  For traction elevators these switches, once set, do not have to be repositioned very often. They can lead to a mis-leveling condition if the car is heavily loaded or for some reason starts to run faster or slower.  If the switches are placed too close together the car will overrun the floor. When they are placed too far apart it increases the floor to floor time causing increased waiting time for the elevators.  Elevators use the same switches in either the up or down direction. Most elevators do not travel at the same speed in the up direction as they do in the down.  A switch will do double duty signaling for a slowdown as well as signaling to speed up.  Stopping the elevator is done by a third switch that tells the elevator that if it cuts the power right now, the car will stop right at the floor.  For those of you who follow baseball think of the stop switch signal as the batter suddenly deciding against hitting the ball in the middle of his swing. Sometimes he can stop it in time and sometimes not. That’s when the umpire calls a strike. If the elevator is traveling a bit too fast or slow the car will miss the floor. One quarter of an inch is acceptable, however that can still cause a trip and a nasty fall.

Some newer elevators use magnets rather than switches. When a pickup on the car passes a magnet placed in the shaft it sends a signal to the controller much the same as the switches mentioned above. In addition to magnets and switches some traction elevators use encoders to pinpoint the position of the car. These encoders are used to verify the position of the car in the shaft and they work in conjunction with switches, magnets or electric eyes to confirm the location of the elevator. Electric eyes are used on some models.  A metal strip with holes in it is hung the length of the shaft and the electric eye sender is placed on one side while the receiver is placed on the other. By this method the elevator can “count” the number of holes that it has passed in any one direction and maintain it’s location within ½ inch.

Additionally some older traction elevators use a cable that travels the length of the shaft with the car. It is tied through a system of gears to a selector. This selector turns at a reduced ratio like a screw. When the elevator arrives at a floor the technician has set switches on the screw to make contact to slow then stop the elevator.  These require constant adjustment due to cable stretching, and things working loose.

In the past control over the stopping of the motor determined much longer transition zones. With the introduction of computerized controls control is much tighter. This reduces the transition zone by a significant amount and results in a much faster floor to floor time for traction elevators.

Hydraulic elevators mainly use the system of switches. They experience different leveling problems mostly due to changes in the viscosity of the oil. If the hydraulic fluid is too cold or too hot it can make a huge difference as to where the elevator will stop. For instance if the serviceman sets up an elevator that is exposed to the outdoors on a frosty day it may not stop level to the floor on a hot summer day if the oil temperature has exceeded the parameters that define a certain viscosity.  Think of viscosity as thickness of the oil. When it’s cold it’s thick and much more difficult to pump. When it’s hot it’s thin and easier pumping translates to faster speeds.  A good example is driving your car, if you cut your ignition at 60 and roll to a stop you will go further than if you cut it at 30. The solution for a hydraulic elevator is to keep the oil within a certain temperature range either by re-circulating (more on this later), or with a tank heater.

This posting is not going to go into every way to stop an elevator, just some of the major methods in use today.  Suffice to say that stopping in the right place is a complex and important issue that you should be aware of and make sure that your serviceman is paying sufficient attention to.

I would like to ask you again if you have any questions, or comments. I have been thinking about possibly working on some software that can write your maintenance plan and tailor it specifically to your equipment and conditions. Please let me know if this is something you may be interested in.  Also if there are any subjects you would like me to tackle next don’t hesitate to comment or email. Otherwise I plan to write a bit about elevator controllers in the next posting.  For questions or comments please contact me at elevatorernie@hotmail.com.

Thank you,

Ernie

Quote of the Day

“An ignorant person is one who doesn't know what you have just found out.”   - Will Rogers

Elevator Doors Continued.......

Elevator Doors continued…

Most of the elevator doors in operation today use either a GAL or a MAC operator. These types of operators transfer the circular motion of an AC electric motor into the linear motion needed to open and close the doors though the use of some cleverly designed control arms. Using links these control arms allow the door motion to reverse when they run into an obstacle or they have reached their open/close limit. This type of door system has been in use for at least fifty years and the technology is well known and proven. Recent developments in the industry have produced DC powered linear door operators with reversible motors that move the doors with a belt system.  The old circular motion door operators used a system of belts too but that was with sets of pulleys to reduce the speed of the motor and increase the power.  The linear systems utilize a long, toothed belt that pushes the door in each direction. The door actually travels along the belt path. This eliminates many of the mechanical components of the door system thereby simplifying it making door maintenance a snap and greatly reducing wear problems.

In the past the geometric configuration of the door components had a huge impact on how well the door worked. The arm connection point on the car door has to be almost exact for the system to work properly. Locate it in the wrong place and the door would always be a real load for the motor causing burned up motors, stalling doors, and other problems. It could also be in a spot that would make some doors too easy to close making them prone to slamming and hard to adjust.  For the first problem companies would just replace a standard operator with a heavy duty one creating the second problem which they consider easier to deal with.  Heavy duty operators were invented for tall doors. The taller the door the more difficult it is to close.  Not only is it heavier, if something gets stuck in the track the leverage factor kicks in and it becomes very difficult to close. Normal elevator doors are 8 feet high. Anything taller than that is more difficult to maintain and requires more attention.  With old style door operators the technician had to adjust the system to be forceful enough to close the heaviest (some main lobby doors are more ornate and thus heavier) or most difficult hoistway door to close. That causes the others to slam. With the advent of new closed loop technology the motor draws just enough energy to allow it to close the door normally, changing at each floor. Many of the systems being manufactured today actually learn the different floor patterns and automatically add or decrease energy when opening or closing on certain floors.

Although most elevator technicians are more comfortable with the old style operators, the new linear operators are gaining wide acceptance. This is due to their simplicity really, there is almost zero maintenance to perform on them. They adjust themselves. Most have switches to control the opening and closing speeds. After an inspection of the belt for wear and lubrication of a very few of the parts the tech can be on to bigger and better things. I also expect them to reduce callbacks over time. One reason being is that if the door doesn’t close all of the way or not firmly enough, the safety switch contact may not be adequate causing either an open circuit or intermittent contact. This condition will shutdown the elevator creating a callback (and probably a bill) for you the customer.  Linear operators are much more consistent.  An added benefit is that engagement of the latch release mechanism and the clutch apparatus is direct. No space is left between the two apparatus to allow pass through. Eliminating the slack in the engagement enables the doors to open silently. How many times have you heard the elevator doors bang when they start to open? A final benefit is that the doors actually use less energy to operate. Although it’s a minute amount, over time it counts.  Not available for all size doors yet, I expect that these will take over soon.

For modernization and upgrade processes there are many “drop in” closed loop replacements for conventional door operators today. These can reduce the cost of an upgrade or mod by a considerable amount by not having to rebuild the entire door closing mechanism. Allowing only the worn parts of the apparatus to be replaced and eliminating the time involved in relocation of components.  Also because all different sizes and types of doors are not yet covered by replacement linear units.

Freight doors come in two types. Hand operated and motorized. The motorized doors operate very differently from the passenger elevator doors.  Both hand and motorized utilize a system of counterweights for ease of opening. Rather than employing relating cables a system of chains is used. Like passenger elevators they have a car door (usually a gate) on the car and a set of hoistway doors at each landing.  These are bi-parting doors, they open horizontally with the top panel going up into the hoistway and the lower panel descending down.  The hoistway doors do not engage the car door. It opens (or is opened ) separately.  In most cases the door operation is activated with a separate button. After the doors are closed you can place a floor call. The elevator will stay at a floor and not answer a hallway call until the doors are closed.  Most are equipped with a bell for signaling that someone on an alternate floor needs the elevator and that the person at the current floor needs to close the doors to get the elevator to move.  Most freight doors have a small window used for checking to see if the car is at the floor.

Freight doors require a lot more lubrication and maintenance than passenger doors. Lack of maintenance can make them very hard to open and close so constant attention is needed.

There are only a few freight door manufacturers around. Almost all of these doors are custom made. To get replacement parts the technician must get the manufacturers name and the serial number from the door panel. For older units this is sometimes difficult because plates have been removed or painted over. Original prints have been lost. In some cases if you can pinpoint the year of manufacture, the original job name (usually the name of the building) and the manufacturer. They can search their files and come up with the original prints for you and assemble a rebuild kit. In the case of hand operated doors they can also offer a kit to motorize the door. There are a few companies out there that do sell replacement parts only but you need the prints and original part numbers to order what’s necessary. Rebuilding freight doors is normally a pretty big job. The components weigh much more and each one is different. They are not as straightforward as passenger doors.

Time to close the book here today. I would like to ask you again if you have any questions, or comments. I have been thinking about possibly working on some software for you to be able to write your own maintenance plan and tailor it specifically to your equipment and conditions. Please let me know if this is something that you may be interested in.  Also if there are any subjects that you would like me to tackle next please let me know. Otherwise I plan to write a bit about elevator controllers in the next posting.  For questions or comments please don’t hesitate to contact me at elevatorernie@hotmail.com.

Thank you,

Ernie

Quote for the day “ If you die in an elevator, be sure to push the UP button.”

Sam Levinson

Elevator Doors

Elevator Doors

The hardest working part of any elevator is the door system.    Every time that elevator moves the doors are required to open and close.  One of the major manufacturers states that eon average elevator doors open and close over 200,000 times per year.  In most elevators that’s a lot of components moving and a lot of wear going on.  I feel that doors are the most important part in the whole system for the simple reason that they are just about the only system the public interfaces with on a constant basis that can cause significant injuries.  Some of you may want to argue about it but doors that are set to operate too quickly can hit passengers. If the safety devices are not operating properly they can catch a hand. Delaminating door skins can catch clothing or cause cuts.  Believe me people can find some of the most unique ways to get injured on elevator doors that you can imagine.

There are many different types of elevator doors, some of which determine the type of elevator. Doors that open horizontally from the center are a part of freight elevators.  Doors that slide vertically are associated with passenger or service elevators.

There are single panel doors, two panel three and four panel doors.  These are known as single, two, three and four speed doors. They open in one direction and the panels fold under each other.  The reason that we call them two, three and four speed doors is because each panel is moving at a different speed. Check it out next time you’re standing there watching a door open.  The door that is furthest from the strike side will move slower than the one at the other end.  This type of door is used to minimize the size of the hoistway while maximizing the width of the doorway.  You see that when the doors of an elevator open they have to have somewhere to go and that’s normally into the hoistway.

There are also center opening doors and they can be either two single panels moving in opposite directions or two, three, and four panels on each side moving in opposite directions.  Known a two (ot three or four) speed center opening doors.

In every passenger elevator you have a motorized car door that travels with, and is part of, the elevator car. At each landing or floor you have a set of hoistway doors.  Hoistway doors are just dead panels. They have no capacity to open by themselves. They may be spring loaded to enhance closing and keep them closed but for the most part it’s just a sliding panel. Normally they are suspended on an overhead track. The doors have rubberized wheels attached to the top that roll back and forth on the track. Center opening doors are “related” by a cable. That means that because they are tied together with a cable whatever the position one door is in the other has to be in the same position as well.  At the bottom of the door you have devices called gibs.  Gibs are for lack of a better word, nubs that stick out from the bottom of the door. These” nubs” travel in a track in the bottom door sill. They clean debris out of the track by pushing it to holes in the sill, but their real purpose os to hold the bottom of the door in place and keep it from swinging in or out.  The motorized car door engages the hoistway doors by means of a clutch assembly.  The clutch sticks out just a bit from the car door and when the car descends the clutch engages two small rubber rollers that stick out from the hoistway door. To fit into the clutch as the car is coming down the rollers compress together which activates a mechanical apparatus that releases the lock on the hoistway doors. All hoistway doors have these locks as a safety measure to prevent  the public from opening the doors and either getting hit by the elevator car or falling down the hoistway.  Most elevators have a single clutch assembly that works the related doors but a few were built in the past that had clutches for each side of a center opening type.

Most passenger elevator doors are equipped with a safety device that will retract the door if it comes into contact with resistance from closing. That is if someone is standing in the doorway or if there is debris in the track that the gibs cannot push out.  They operate on a mechanical basis and they have to be checked regularly by a technician to insure that they generate no more than thirty pounds of force before the door motion is reversed. Some do get out of adjustment and they can give you a nasty smack if you’re not careful. Many of these types are accompanied by a set of electronic eyes that are placed at 5 inches above the floor and twenty nine inches above the floor. All you have to do to retract the door is to break either beam of light.  About twenty years ago the manufacturers improved on the beam idea by installing a device that projects many infrared beams from about 3 inches to 80 inches above the floor. These are non contact edges and are mostly what we see in elevators today.  Although the doors still have to be set to retract at a maximum of thirty pounds in the event that the device fails.  Elevator codes state that doors that are equipped with electronic eyes and infrared beams must include a feature called “nudging”. Quite a few electronic edges were installed when they first hit the market on elevators that didn’t have the nudging capability. Most of those have been weeded out through modernization and diligent state inspectors.  The nudging feature is utilized in the event that the door is blocked by something or someone or mainly if the beam is obscured by smoke from a fire.  After a set period of time an alarm sounds and the door will begin to close slowly. It still is set to no greater than thirty pounds of closing force in the event that someone may be lying in the doorway incapacitated.

Doors have so many moving and constantly wearing parts they account for at least 80% of the elevator failures today. Most of the time an elevator fails to operate due to a signal from a safety circuit. Think about it, for your elevator to operate the car door has to be closed completely and the contacts in the safety circuit providing a closed loop.  Each set of hoistway doors also has a set of contacts that are tied to the safety circuit. If they don’t complete the loop due to something like an excess of pressure in the building, a worn closer that needs the spring tightened, corroded contacts in the circuit, or any other reason that everything is not closed up tight, the elevator will not run.  We in the elevator business think that’s a good way to do things, we realize that the public is somewhat annoyed by this.

I’m out of time right now but I will be adding to this very soon. In the meantime don’t hesitate to leave a comment or send me a question at elevatorernie@hotmail.com.

Today’s quote comes from Will Rogers.

“Everything is funny as long as it is happening to somebody else. “

Some Other Types of Elevators

Some Other Types of Elevators

There are many other types of elevators in use today. Wheelchair lifts operate mainly from  screw drives.  Just envision a big screw and the car is attached to the nut on the screw. As the motor turns the screw it raises or lowers the car. Most are unsophisticated and only stop at a top or bottom limit. These are defined as LULA lifts (Limited Use Limited Access).  They do have safety devices installed if, for instance, the gate is not closed the unit will not run. The gate locks between floors to prevent falling out or getting hooked on something during movement. Most have a safety switch on the bottom to stop the unit if it’s descending onto something in the pit to avoid crushing it. Other wheelchair lifts are stair climbing type devices. They ride along a rail mounted parallel to the stairway and accomplish movement by a set of cables. This type is usually complex. They will fold up against the wall after use to avoid taking up space.  When activated they drop down to allow the rider to roll onto them, then a safety bar positions itself across the entrance to prevent the rider from rolling out while moving.  

A really cool device that we don’t see much of here in the US is the funicular. I like to think of it as a cross between a streetcar and an elevator. Funiculars are used in urban areas where there are steep hills. The car is pulled up and let down by cables just like an elevator but it rides on rails just like a streetcar. Of course conventional elevators have rails too but those are used to steady the car during the vertical movement process.

There are also dumbwaiters, way too small for people to ride in. They can be hydraulic or traction and most have doors that open horizontally at the middle. Meaning the top half goes up and the bottom half goes down.  Dumbwaiters are not designed for passengers all controls are at the hall stations. The way to operate them is to load them, close the door then press the destination button.

A similar device is a material lift. The “car” usually consists of a cage. They are mostly hydraulic/chain driven like the portable hoists that mechanics use in garages now.  Material lifts like dumbwaiters are not built for passenger use therefore they have no controls inside the cage and the destination is determined by an operator at a hall station.

Construction sites use rack and pinion type elevators that are set up for temporary use. They are designed to carry passengers and materials to upper floors on construction projects. To understand their operation, just visualize a gear climbing a toothed rail. The motor travels with the car. These are very heavy duty and get tons of abuse on sites. The passenger/freight compartment is just a cage and for those who are afraid of heights can provide a load of thrills.

There are other types of elevators but for now these are the ones you’re most likely to see.

My next post will be on the hardest working system in any elevator….the doors.

Please let me know what you think of this blog along with any questions that you may have or any suggestions for subjects that you think everyone would like to see information on.

Remember that’s  elevatorernie@hotmail.com

Regards,

Ernie

“Sometimes I wonder whether the world is being run by smart people who are putting us on, or by imbeciles who really mean it”  -----Mark Twain

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