May 23, 1994
CIRCULAR LETTER E-94-2
TO: Elevator Companies, Elevator Inspectors
and Other Concerned Parties
SUBJECT: The Stopping of Hydraulic Elevators
California Elevator Safety Order 3071(d) reads as follows:
Electrical Protective Devices. In addition to the terminal stopping devices required by section 3070, the following electrical protective devices shall be provided and shall conform to the requirements of section 3040(b), except that their operation shall cause the electrical power to be removed from all control valves and from the pump motor.
Exception: Devices (4), (5), and (6) need not to remove the power within the leveling zones.
Most hydraulic elevators being installed use a direct coupled pump. With the direct coupled pump removing the power from control valves and pump motor can cause a sudden stop and rough start, if the power is turned right back on. To eliminate the sudden stop some elevators are being provided with a system that would allow the pump motor to run for a limited time, after the interruption of an electrical protective device. This time delay is to provide what is commonly known as a "soft stop".
The Division had an opportunity to test an elevator with a rated speed of 100 F.P.M. with and without the soft stop. With the soft stop, it took approximately 20 in. after the activation of the car stop switch for the elevator to stop in the up direction. Without the soft stop, the elevator stopped suddenly. Obviously, the 20 in. stop is smoother than the sudden stop.
Circular Letter E-94-2
May 23, 1994
Subject: The Stopping of Hydraulic Elevators
When one of the devices listed in 3071(d) is activated, there is an unsafe and/or emergency condition and the elevator must stop. Hydraulic elevators do not travel at a speed likely to cause injury in the event of a sudden stop.
The Division must enforce the ESO as written. If there is concern over hydraulic elevators stopping suddenly, the Occupational Safety and Health Standards Board may be petitioned for a change to the ESO.
W. E. McTiernan
Principal Safety Engineer
DOSH - Elevator, Tramway, and Amusement Ride Unit