for globe and angle valves. Valves shall open fully or close
tightly without requiring further attention when actuating control
is moved to the open or closed position. A predetermined thrust
exerted on the stem during operation resulting from an obstruction
in the valve shall cause motor to automatically stop. Power
operators shall be complete with gearing and controls necessary
for size of valve being provided. Power operators shall be
designed to operate on the [electric] [compressed air] power
supply indicated. Provide power operators with remote position
indicators on the following valves: soot blowers, [_____], [_____].
(2) Floor Stands and Extension Stems: Floor stands shall be cast
iron or steel, constructed for bolting to floor and shall include
an extension stem, an operating handwheel and a position indicator
for non-rising stems. Floor stand shall be not less than 762 mm
30 inches high. Handwheel shall identify rotation direction for
closing valve and shall be of such diameter as to permit operation
of valve with a force of not more than 18 kg 40 pounds. Extension
stems shall be corrosion resisting steel designed for rising and
non-rising stems, as applicable, and for connection to valve stem
by a sleeve coupling or universal joint. Provide in length
required to connect valve stem and [handwheel] [operating
mechanism] and of sufficient cross section to transfer torque
required to operate valve. Provide floor stands and valve
extensions on floors and platforms for the following valves:
dearator drain valves, [_____] [_____].
(3) Provide motorized actuators or chain wheels with chain and
guides on valves with handwheel centerline higher than 2 meters 7
feet above floor or platform except where specified otherwise.
Chainwheel operator shall be fabricated of cast iron or steel and
shall include a wheel, endless chain and a guide to keep the chain
on the wheel. Provide galvanized steel endless chain extending
from valve to within one meter 3 feet of floor or platform.
Provide impact chain wheels on steam headers and other locations
where the valve has a tendency to stick. When a valve is
motorized, provide hand operation for emergency.
(4) Provide gear operators on ball valves larger than 80 mm 3
inches and on gate valves 200 mm 8 inches and larger.
f.
Steam Pressure Regulating Valves: FS A-A-50558, minimum of Class
[125] [150] [250] [300], except as specified otherwise. [Cast
iron], [cast steel] valve body with valve seats and disc of
replaceable heat treated stainless steel. Valves shall be single
seated, shall seat tight under dead end conditions, and shall go
to the closed position in the event of pressure failure of the
operating medium. Valves shall be spring loaded diaphragm
operated type, except valves exposed to ambient temperature of
less than 2 degrees C 35 degrees F or exposed to the weather shall
be piston operated type. Capacity of valves shall be not less
than that indicated. Pilot valves shall have strainer at inlet
from external feeder piping:
(1) Spring Loaded Diaphragm Operated Valves: Fabricate main
spring of stainless steel, and it shall not be in the path of
steam flow through the valve. Control valve by pilot valve
through external feeder piping.
SECTION 15501N
Page 142
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