Building Design and Construction Handbook - Merritt - Ventech!

11.136 SECTION ELEVEN
The security feature of the cylinder lock results from the fact that only one series
of notches in the key will correspond to the respective lengths of the several individual
pins. With as many as five or six tumblers, it is apparent that many combinations
are available.
By using split pins, different keyways, and various sizes and arrangements of
the pins, master keying and grand master keying of cylinder locks are made possible.
Thus one master key may be made to open all the separate locks on each
floor of a building, while a grand master key will open any lock in any floor of
that building. In case there are a number of such buildings in a group, a great-grand
master key can be made that will open any door on any building in the group.
Security Precautions. The security of a building from the standpoint of unauthorized
entry and life safety is affected by the proper selection of hardware. Although
locks are important for security, the total system, including the building
design, must be considered. A lock installed in a door that is loosely fitted in the
frame may be ineffective. Hollow metal and aluminum frames that are not reinforced
and anchored properly are easily ‘‘spread,’’ and undetectable entry can result.
In high levels of master keying, more split pins must be used, and thus more
‘‘shear lines’’ are established. This makes the cylinder easier to pick. Hence, unnecessarily
complicated master key systems should be avoided.
A good security lock is available with a dead bolt and a deadlocking latch bolt.
Both bolts are retractable in one operation, merely by turning the inside knob. This
satisfies requirements for security against unauthorized entry and life safety.
Hardware requirements for life safety and fire doors are covered by two National
Fire Protection Association Standards, ‘‘Life Safety Code’’ and ‘‘Fire Doors and
Windows.’’ Both are incorporated in many building codes.
11.68 WINDOW HARDWARE
Sash balances are commonly used with double-hung windows as counterweights
instead of weights and pulleys. Some balances have tape or cable with clock-type
springs, which coil and uncoil as the sash is raised and lowered. Another type
employs torsion springs with one end fixed to the side jamb of the window and the
other arranged to turn as the sash goes up or down. The turning device in this type
of balance may be a slide working in a rotatable spiral tube, or it may be a slotted
bushing attached to the free end of the spring and fitted around a vertical rod
attached to the sash. This rod (Fig. 11.83) is a flat piece of metal twisted into a
spiral shape. The up-and-down movement of the sash causes the slotted bushing to
revolve on its spiral sliding rod, thus winding and unwinding the spring. Still another
type utilizes a vertical tension spring of the ordinary coil variety. One end of
the spring is fixed and the other is fastened to the sash; the spring stretches or
compresses in a vertical direction as the sash is moved up or down.
Some sash balances combine weather-stripping with the balances. Others have
friction devices to hold the sash in the desired position.
One patented type of sash balance known as the Unique sash balance incorporates
a clever counterbalancing feature by making a change in the degree of pitch
of the spiral rod from top to bottom, thereby controlling the increase and decrease
of spring tension (Fig. 11.83). The pitch varies from 30 to 80�. As the spring turns,
the changing spring tension is automatically compensated for by the variable pitch