Building Design and Construction Handbook - Merritt - Ventech!

14.62 SECTION FOURTEEN
FIGURE 14.21 Water-supply piping for sprinklers.
pipe hanging since the branch lines, which out number the mains, can be hung
directly off the joists. Where construction is concrete pipe hanging is an easier task
but one should give consideration to the arrangement of beams and bays such that
unnecessary fittings and pipe lengths can be avoided.
Drainage of Sprinkler Systems. Provisions must be made for draining all parts
of a sprinkler system. For that purpose, valve-controlled drains must be provided
at low points in the system. The primary drain for most sprinkler systems is the
main drain, normally a 2 inch drain located at the system riser. All drains should
discharge directly to outdoors or to a sump capable of handling full flow drain
capacity.
Special consideration must be given to the drainage of dry-pipe systems and
portions of preaction systems subject to freezing. The branch lines of these systems
should be pitched 1 ⁄2 in per 10 feet and mains 1 ⁄4 inch per 10 feet of length towards
a suitable drain connection to accommodate total system drainage. Where trapped
piping in dry-pipe systems exceeds 5 gallons capacity, a means must be provided
to drain the trapped area without accidentally tripping the dry-pipe valve. This is
usually accomplished with use of a drum drip assemble, an assembly which permits
isolating trapped water and draining it without loosing air pressure.
Inspector’s Test Connections. All sprinkler systems should be tested periodically
to ensure their proper function. A test connection for wet- and dry-pipe systems
consists of a connection at least 1 inch in diameter with a test valve terminating in
a smooth-bore, corrosion-resistant orifice. This orifice connection should be sized
to provide a test flow equivalent to the smallest orifice size sprinkler installed in
the system. For most systems the test valve connection can be located anywhere
down stream of the alarm valve or flow switch, whichever is provided; however,
on dry-pipe and double-interlock preaction systems the alarm test valve must be
located at the hydraulically remote point of the system. This is to ensure that water
will reach the remote end of the sprinkler system without undue delay, usually 60
seconds for large systems.
Approvals of Sprinkler-System Design. In all cases, before a sprinkler system is
installed or modified, the applicable drawings and hydraulic calculations should be
submitted to the authority having jurisdiction and the insurance underwriter as nec-