air system shall include two full-capacity seal air fans, one operating and
one standby. Each fan shall be capable of supplying two times the
guaranteed cfm leakage rate through the dampers at design conditions. Fans
shall be as specified. Each fan shall be capable of maintaining a pressure
between the seal chamber and the gas stream of at least 747 Pa 3 inches W.C.
at the design conditions. Provide zero leakage isolation valves at the
discharge of each fan. Valves shall be mild steel gate or butterfly
valves. Provide check valves at the discharge of each fan to prevent
backflow through the idle fan. Check valves shall have a replaceable soft
fluoroelastomer seat, and shall be designed to prevent "flutter" when in
the open position. Provide a manual control damper or valve in the seal
air duct to permit seal chamber pressure to be controlled. Control damper
or valve shall be mild steel, and shall have an easily visible position
indicator. Provide an automatic isolation valve in the seal air duct to
permit seal chamber pressure to be controlled. Control damper or valve
shall be mild steel, and shall have an easily visible position indicator.
Provide an automatic isolation valve at the connection of the seal air duct
to the seal air chamber. Valve shall be gate or butterfly type constructed
of nickel-chromium alloy containing a minimum of 55 percent nickel, 20
percent chromium and 8 percent molybdenum and shall be suitable for
corrosive environments. Provide pneumatic piston operator on the valve to
operate on 552 to 862 kPa (gage) 80 to 125 psig instrument air. Tube and
mount a four-way dual-coil solenoid valve, with Class H coils rated for
120-VAC service. Provide two dual-pole-dual-throw limit switches, one to
actuate in the open position, one to actuate in the closed position. Limit
switch housing shall meet NEMA 4 requirements. Piston actuator shall
remain in last position if air supply fails. Provide three 50 mm 2 inch
pipe nipples with caps and rod-out on the seal chamber of the damper,
preferably on top of the damper, for attachment of seal chamber pressure
instrumentation. Provide necessary instrumentation to monitor operation of
seal air system and initiate alarm as specified for maintenance personnel
protection. Provide 50 mm 2 inch port with rod-out on seal chamber and 50
mm 2 inch port with rod-out on ductwork to test seal air pressure
differential. Port on ductwork shall extend 150 mm 6 inchesbeyond
stiffeners to clear insulation and lagging. Provide caps or plugs. Seal
air systems, where possible, shall be mounted on the damper frame.
Installation shall be such that the system is easily accessible and
instrumentation can be easily observed. Install such that there is
complete access to linkages, drive units, bearings, and stuffing boxes.
Isolation valve and blower shall be mounted such that condensation
occurring between the damper and the isolation valve flows into the
ductwork. If installation on the damper frame is not possible, a platform
shall be provided to support the equipment.
2.11.3.2
Louver Dampers
Damper blade/shaft assembly shall be designed not only for the maximum
allowed stress, but to limit the deflection under the maximum conditions at
which the damper is to seal to L/14.4 or 6 mm L/360 or 1/4 inch, (whichever
is less)(L = blade length in mm inches). Blade shall be of a rigid
structural design, capable of handling thermal stresses and warping due to
differential temperatures and pressures, without affecting damper
operation. Stub shafts shall be pinned or bolted to the through shaft or
blade in such a manner that individual damper blades can be easily removed.
Pins or bolting materials shall be of carbon steel, with a design such
that the connections are self-locking. Shafts shall be sized to deliver
the full operator torque to any one blade, without exceeding one-third of
the shaft yield stress when operating at the worst-case design conditions.
Provide dust-tight stuffing boxes sealed with fluoroplastic packing
SECTION 15864N
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