For added protection Stanley recommends the installation of an Over speed Valve (OSV), (Also referred to as Pipe Rupture Valve). It is designed and can be adjusted in the field to stop the elevator in the event of an over speed condition caused by a broken supply line or an abnormally high rate of oil flow between the OSV and the power unit. The OSV will not stop the car from over speeding due to underground cylinder leaks and is not a substitute for cylinder replacement or other safety devices.
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Massachusetts’s law permits you to fit your existing system with governor-operated safeties or a plunger gripper. Traditional governor operated safeties common to traction elevators are generally not a structurally viable option. Recent design advances have introduced plunger gripper technology as an alternative to conventional safeties. Like traditional safeties this electro-mechanical device detects downward over speeding or unintended movement of the car. In this event safety shoes will be activated, closing around the hydraulic piston and bringing the car to a controlled stop. It is designed to provide protection against over speeding cars and failures of any component in the pressure system, including valves, piping, hoses and packing gland.
While the hydraulic elevator safety will prevent the elevator from falling,it does not protect or guarantee the integrity of the cylinder. In the event that an underground leak actually develops, your cylinder must be replaced.This is a new technology that will require additional testing and regular maintenance beyond that currently required. This option is not available to all hydraulic elevators at this time. It will only fit hydraulic pistons between 3.5 and 8 inches, with a maximum weight capacity of 11,000 to 30,000 pounds (gross load). In many cases it can not be installed due to code required clearances. Considerations for the legal application of the plunger gripper will vary depending upon the age of the equipment, the particular safety features present and other characteristics of the existing system.