Chapter LXXI: Section 81: Safety Appliances for Various Uses

FOR HOIST CAGES, &c.

=1492. Cam gear;= operates by gripping the wood guides by a serrated eccentric cam surface on the breakage of the rope, the cam being pulled round by a spring which is kept out of action by the tension of the rope until it breaks.

=1493. Strut or pawl gear;= explains itself.

=1494. Double wedge gear.=

=1495. Governor gear.= The rope attached to the cage drives a governor acting on a brake or catch which is thrown into action if the cage gains excessive speed, used in Attwood Beaver’s Patent; American Elevator Co., &c.

=1496. Rack and pawl gear.=

=1497. Cross grip lever gear.=

=1498. Safety hook= to prevent accident from overwinding; the projecting horns ~A A~ strike the edges of the plate ~B~, and throw the shackle ~C~ at top out of gear.

=For hoist doors= the best appliance is an ordinary spring lock opened
only by a key, the doors being provided with springs to close them.
Various automatic doors, revolving shutters, and other devices have
also been tried. A simple and effectual protection is a continuous
open-work screen wound upon a roller at top and bottom of lift, and
attached to the top and bottom of cage and rising and falling with it,
so that the doors into lift are all covered at all times except the
one at which the cage happens to stand.

=Safety valves= (see Section 89). Various automatic alarm signals are
applied to boilers to warn against low water or excessive pressure.

=Automatic valves= and other devices are applied to pumping and steam
engines to prevent running away. See note to Section 41.

Section 82.--STEAM TRAPS.

To collect and discharge condensed steam from pipes, &c.

=1499. Trap operated by a modified form of ball cock,= which rises as the box fills with condensed water and opens the discharge valve.

=1500. Effects the same object by a floating basin.= The condensed water enters the box outside the basin, fills it, and lifts the basin which closes the discharge outlet; when the box is full the water overflows into the basin and sinks it, thus opening the outlet valve.

=1501. Trap operated by expansion= of a bent spring which closes the valve, on the principle that live steam is hotter than the water condensed from it.

=1502. Tredgold’s trap.= The valve is opened by a simple float.

=1503. Wilson’s trap,= like 1501, is dependent on the different expansion of a spring under the difference of temperature of the steam and condensed water. In this case the spring is formed of a steel and brass plate riveted together.

There are many other forms upon similar principles to the foregoing.