Apparatus for safely installing and removing spring failsafe...

Fluid handling – Processes – Cleaning – repairing – or assembling

Reexamination Certificate

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Details

C137S015180, C137S315030, C137S315270, C092S13000R, C251S063600, C251S129040, C251S129110

Reexamination Certificate

active

06182678

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a failsafe mechanism for rapidly returning a switch to an off position in the event the switch actuator fails when the switch is in an open position.
The term switch, as herein used, means any type of device that reciprocates between a first closed position and a second open position. An example of such a switch is a valve stem that closes the valve when in a first position and opens the valve when the stem is moved to a second position. Many valves are placed in generally inaccessible locations and are remotely positioned through a central control station. Electrically controlled linear actuators are typically connected to the stem of valves that operate to control the flow of fluids (liquid, gas or vapor) through the system. In the event of a power failure or a system failure, it is highly desirous to rapidly close all of the valves in the system to shut the system down and thus prevent damage from occurring. To this end, many spring loaded devices have been developed that act upon the valve to automatically close the valve when either the actuator fails or a shut down signal is sent to the actuator.
Although many of these spring equipped failsafe devices work well in practice, it has long been a problem to quickly and safely mount or dismount the device upon a valve because of the typically high spring forces involved. The inability to contain the spring in a compressed state can create a potentially dangerous situation.
SUMMARY OF THE INVENTION
It is an object of this invention to improve failsafe devices, and in particular, failsafe devices that are actuated by a spring that is mounted in a loaded condition against a switch to rapidly open or close the switch in the event of a system failure.
It is a further object of the subject invention to safely mount and dismount a compressed failsafe spring upon a switch.
A still further object of the present invention is to provide an improved spring loaded failsafe mechanism for use in association with a valve.
Yet a further object of the present invention is to safely install and remove a spring actuated failsafe actuator on a valve.
Another object of the present invention is to provide for ease of maintenance of a valve that is equipped with a spring loaded failsafe device.
Yet another object of the present invention is to lessen the down time required to maintain a valve equipped with a spring loaded failsafe device.
These and other objects of the present invention are attained by means of a failsafe device that includes a frame that contains a top end wall and a bottom end wall that are mounted in a spaced apart relationship by a plurality of columns. The stem of a linear function switch passes upward into the frame through the bottom end wall through a clearance hole provided in the end wall. The stem is movable over a reciprocal path of travel between a first closed position and a second fully opened position. A spring seat is attached to the stem for movement therewith and a compression spring is passed downwardly through the top wall of the frame into contact with the spring seat. A cover plate is placed over the top of the spring and is brought down in contact with the top end wall to compress the spring inside the frame and thus urge the stem into the closed position.
A linear actuator is mounted in the cover plate that contains a rod that is connected to the stem and is arranged upon demand to move the stem from the closed position to the open position wherein the spring is further compressed and to return the stem to the closed position. In the event the actuator fails, is shut down, or experiences a power failure while the stem is in an open position, the compress spring will take over to rapidly move the stem to a closed position.


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