A switch stand operates to move a pair of switch points between two (2) stock rails to divert rolling stock from one track to another. A typical switch stand consists essentially of a base, a spindle and a throwing lever. The switch points are moved between the stock rails by moving the throwing lever through part of a circle in a horizontal plane to impart directly a rotary motion to the spindle. A crank on the foot of the spindle serves to convert the rotary motion of the spindle into rectilinear movement of a connecting rod attached to a switch rod mounted between the switch points. Thus, movement of the throwing lever by an operator from one to another of the two operating positions for the switch stand causes corresponding movement of the switch points from one stock rail to another.
In recent times there has been a dramatic increase in federal employee liability actions for alleged back injuries resulting from the exertion of heavy forces to operate throwing lever style switch stands. Over the years the force requirements to operate switch stands have increased substantially. These increased force requirements have been caused by the weight of rail sections increasing from between eighty and ninety pounds per yard to a range of one hundred thirty-two to one hundred thirty-six pounds per yard now in common usage. Additionally, speeds of trains through turnouts have increased requiring the use of longer turnout configurations which in turn have required longer, heavier switch points. Furthermore, with the combination of heavier rail sections and longer switch points, the frictional forces within switch points have increased, again causing the force requirements to operate a switch stand to increase.
It has been found that track equipment has been less well maintained and adjusted in recent times which also contributes to the increased force requirements required to operate switch stands. A situation further compounding the problem of back injuries occurring during operation of switch stands has been the decline of experienced railroad personnel necessitating the use of less experienced people operating switch stands.
In order to reduce the incidents of federal employee liability cases alleging back injuries occurring during operation of switch stands, railroads have begun to demand switch stands requiring less operator force for operation. Existing manual lever switch stands have mechanical advantages in the range of six to seven. A mechanical advantage of six has been a recommended minimum by the American Railway Engineering Association based upon an average load of eight hundred sixty-four pounds of force required to move a pair of switch points. With this criterion a theoretical operator force of up to one hundred forty-four pounds may be required to be exerted to operate a switch stand between its two operating positions. In practice, current switch stands have been found to have a mechanical advantage of approximately nine to one. Such stands require a manual force by an operator of approximately ninety-six pounds for operation.
Preferably a switch stand would incorporate a large mechanical advantage to thereby require a minimum manual force to be applied by an operator to move a switch stand from one operating position to another. Such a switch stand also should be self-locking in each operating position, should have a stop to prevent further spindle movement for each operating position and should provide an easily replaceable part designed to fail during accidental "trail-through" to protect internal components of the switch stand from damage.
USPTO Backgrounds
USPTO Backgrounds