2.1.20.3
Back Pressure Relief
ASME PTC 25 back pressure relief valve shall have stainless steel or cast
steel body with valve internals and seats constructed of stainless steel.
Back pressure relief valve shall have guides and shall be positive closing.
Adjustment of the desired back pressure shall cover a range between 14 and
70 kPa 2 and 10 psig. The adjustment shall be effected externally and any
shafts extending through the valve body shall be provided with adjustable
stuffing boxes having renewable packing. Back pressure relief valve shall
be self contained, internal pilot piston operated. An external positioner
shall be provided on each valve.
2.1.20.4
Blowoff and Quick Opening
Blowoff and quick opening valves shall be as required in ASME BPVC SEC I.
The valve shall be the balanced seatless type or the double seated rotating
disk type. Quick opening valve shall be the straightway type. Blowoff and
quick opening valves shall be designed for a working pressure of 2.06 MPa
(300 psig) 300 psig and shall be suitable for safe blowdown through the
installed piping system.
2.1.20.5
Pressure Reducing
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NOTE: Valves requiring tight shutoff for steam
service will be ANSI Class IV. Where a
thermostatically controlled valve is installed after
and near the reducing valve in a manner to cut off
the passage of steam, valves with ANSI Class IV
shutoff will be used. Where valves are used for
reducing pressure to the deaerating heater, valves
will have ANSI Class IV shutoff.
Consider silencers in pressure reducing valve trains
where acoustics to adjacent spaces or maximum noise
level in mechanical room is an issue.
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Pressure reducing valve shall be designed for a working pressure of not
less than 1.03 MPa 150 psig, and shall be quiet and nonsticking in
operation. Pressure reducing valve shall be spring loaded, internal pilot
piston operated type with an external position indicator. Pressure
reducing valve body 65 mm 2-1/2 inches and larger shall be cast steel.
Pressure reducing valve shall have raised face flanges to match the raised
face flanges on connecting piping. Pressure reducing valve 38 mm 1-1/2
inches and smaller shall be bronze with screwed connections. Pressure
reducing valve trim shall be stainless steel or monel metal. Parts subject
to wear shall be renewable. Pressure reducing valve shall have seat and
plug faced with cobalt tungsten carbide mixture, or made of heat treated
stainless steel or high chromium steel. Seat and plug facing shall have a
Brinell hardness of not less than 450. Pressure reducing valve shall be
designed for dead-end service. Resulting noise level shall not exceed
[_____] dBA.
2.1.20.6
Plug
Plug valve shall be tapered plug, lubricated type. Lubricant shall be
suitable for the intended application. Body shall be cast steel. Plug
shall be carbon steel. Pressure class shall be minimum ANSI Class 150.
SECTION 15561A
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