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