An elevator is an incredibly simple contraption; however, modern freight and passenger hydraulic elevators are somewhat more elaborate with complex mechanical systems to handle substantial weights. They also have control mechanisms that can be handled by operators or passengers, as well as safety devices to avoid the risk of a catastrophe. Direct-acting hydraulic elevators have been part of the vertical transportation industry for more than 100 years.
Originally they were used primarily for freight, but over the past 50 years, they have become the popular choice for passenger as well as freight applications due to their dependability and cost efficiency. Over the years they have proven their worth in North America alone with an estimated 500,000 installations. The advantage of not needing an overhead building structure for its primary support has made hydraulic elevators more cost-effective than traction or electric elevators. They are able to operate to impressive heights with high speeds and a large loading capacity.
Today there are two major designs in common use: Hydraulic and Roped elevators.
Hydraulic elevators lift a car by using a hydraulic ram (a piston mounted in a cylinder that is fluid-driven) connected to a pumping system. Typical hydraulic systems use oil or other incompressible fluids. There are three parts to a hydraulic system:
1. A fluid reservoir (a tank).
2. An electrically powered pump.
3. A valve situated between the reservoir and the cylinder.
Elevator System Performance Testing
Pre-testing is designed to prevent time and money wastage and intended to determine whether the elevator is ready for the final inspection. Very few deficiencies found will result in aborting a test.
Testing of newly installed elevators can be extremely dangerous and the risk of injury increases without previous experience of testing elevators. All observations and measurements can be done with the assistance of an elevator mechanic from outside the hoist way and the mechanic must first verify that the safety circuit is functioning properly. The elevator mechanic must also check that the hoist way door interlocks, the gate switch, the stop switches, the final run-by limit switches, and the top emergency exit switch are open to stop the elevator and prevent it from running until the switches have been closed.
Constant vigilance is needed when testing a traction elevator for correct speeds. In the machine room be aware of the danger of rotating equipment such as the pump motor and the hydraulic pump. The belt-driven combination may start at any time without warning. Other dangers include the obvious risks of falling, tripping, and electrical shock.
– Observe that all hall and car position indicators, hall lanterns, and push buttons are operating;
– Check that the car floor-levelling is within 1/8” at full capacity and empty loads;
– Check that the communication system is working. The car communication system must be an ADA hands-free telephone system.
– The elevator must have a Phase 1 and 2 Fire and Smoke detector system which are code and should function as per ASME. No elevator with code violations can pass the test.
Hydraulic Elevator System Performance Testing
- Observe through the bottom hoistway that the automatic shutoff valve is installed closely to the jack assembly head. Victaulic fittings should not be used between the shutoff valve and the jack.
- Obtain verification from the elevator contractor that all fittings and piping are according to specified size before testing the entire system at twice the working pressure.
- Test the automatic shut-off valve by placing the rated capacity on the car and carrying out a terminal-to-terminal run. The elevator mechanic should then activate the automatic shut-off valve. Observation is done through the bottom hoist way with the door lock bypassed. Activation will be caused by overspeeding or overloading or both. Under no circumstances should the pit be entered during the testing period, from the start of the terminal-to-terminal run until the test has been completed.
After the automoatic shut-off valve has been successfully activated the elevator should be run up and the elevator mechanic should reset the valve. The overloading or overspeeding condition should then be removed and another three terminal-to-terminal runs conducted. Remember to remove the circuit bypass device used during the test and no-one should enter the pit during the loading of weights until the end of the test. Should the automatic shut-off valve be adjusted during the test for any reason, the test must be restarted.
- Check the amperage of the pump motor with an Amprobe or an ammeter in the controller. Readings should be taken with full capacity on the up-run. A reading of more than 10% of the amperage rating on the motor that is stamped on the data-tag is an indication that the size of the motor is insufficient for the load and needs to be replaced. Regarding the pump size, experience has indicated that a rating of between 40 – 60 horsepower is needed for the successful operation of standard level elevators that are rated at 4,000 and 5,000 pounds capacity. Rarely has a 30 horse power motor proven adequate.
- Test the pressure by first determining that the gauge is in the machine room for reading the pump pressure-to-jack assembly. The pressure should not exceed 500 Psi with full capacity on the up-run.
- Ensure that all specified devices such as the shut-off valves, muffler, and gate valves are properly installed when the unit is being tested. Any addition to the hydraulic pipe usually causes increases in the pump motor amperage and the working pressure. If any changes have been made to the pipe run the pressure and amperage readings should not be noted down until all changes have been completed.
- Conduct a 1-hour performance test – take temperature readings of the hydraulic oil, the pump motor and the machine room with rated capacity, then start the 1-hour test. The doors should operate at each stop at every floor with an accuracy of approximately 1/8″ observed at the start as well as the completion of the test. If the test cannot be run for one hour without adjustments or repairs it is not ready for a final inspection. A one-time shut-down that has a simple solution should not necessarily abort the test, however, repeated shut-downs indicate that the elevator is not ready for final testing.
- At the completion of the 1-hour test, the elevator should be stopping level without reveling operations, in both directions. The harshness of stopping or starting or obvious changes in the floor levels are indications of major problems. The excessive rise in temperature ratings also indicates that a final test should not be carried out.
Electric Traction Elevator System Performance Testing
1. Check the controller amperage with an amprobe or ammeter. Readings should be taken in both directions with full capacity and no load. Readings that measure more than 5% over the data tag number located on the machine indicate major motor problems.
2. Check for car safety. After taking the speed governor, or ascertaining that it has been properly set and attached, run a demonstration of the safeties with an empty car. The elevator should be activated by the mechanic and run in the downward direction at inspection speed to a point where, when manually tripped, the car safeties will be activated by the speed governor and wedge onto the guide rails.
3. Conduct a 1-hour performance test. Load the elevator to full capacity and record the temperature of the machine room and the hoist motor. Run the 1-hour performance test in the same manner as described for hydraulic elevators. After completion of the 1-hour test look for changes in the smoothness of stopping and starting and the accuracy of floor stops. When the brake is lifted check for roll-back. Any failures or repeated shut-downs indicates that the elevator is not yet ready for final inspection.
4. Conduct buffer tests by having the counterweights and car strike the buffers on an empty load at inspection speed. After each test, check that the buffer returns to its original height within ninety seconds. Check for excessive oil leakage.
5. Excessive oil leakage will be indicated by oil sprayed on the pit walls during the buffer test, or oil observed dripping from the car frame of the elevator after striking the buffers. These conditions would require repairs or replacement of the buffers before a final test can be conducted.
6. Any items or parts that need to be replaced due to failure during the pre-test period that would cause a change in the electrical or hydraulic system of the elevator would have to be pre-tested again before a final test is scheduled.
While elevators are considered to be extremely safe and reliable, it is only through thorough testing and inspection that they can be deemed to be so. A malfunctioning elevator may potentially cause serious injury and even loss of life.
Many elevators are old and may not have the necessary maintenance and inspection records in place, or lack the safety features required today by code. Conformance to safety codes developed by ASME (American Society of Mechanical Engineers) is a vital requirement, as well as elevator system performance testing.