| (C) Type of stop valve. When stop valves over two inches
in size are used, they shall be of the outside screw-and-yoke rising
stem type or of such other type as to indicate at a distance whether
it is closed or open by the position of its stem or other operating
mechanism. The wheel may be carried either on the yoke or attached
to the stem. If the valve is of the plug cock type, it shall be fitted
with a slow opening mechanism and an indicating device and the plug
shall be held in place by a guard or gland.
(6) Drain valve.
(A) Each hot water heating boiler shall have one or
more drain connections, fitted with valves or cocks connecting to
the lowest water containing spaces. The minimum size of the drain
piping, valves, and cocks shall be 3/4 inch nominal pipe size (20
mm). The discharge piping shall be full size to the point of discharge.
When the blowoff connection is located at the lowest water containing
space, a separate drain connection is not required.
(B) Minimum pressure rating. The minimum pressure rating
of valves and cocks used for blowoff or drain purposes shall be at
least equal to the pressure stamped on the boiler, but in no case
less than 30 psig (207 kilopascals). The temperature rating of such
valves and cocks shall not be less than 250 degrees Fahrenheit (121
degrees Celsius).
(7) Provisions for thermal expansion.
(A) Heating systems with open expansion tank- An indoor
overflow from the upper portion of the expansion tank shall be provided
in addition to an open vent, the indoor overflow to be carried within
the building to a suitable plumbing fixture or basement.
(B) Closed heating system.
(i) If the system is of closed type, an airtight tank
or other suitable air cushion that is consistent with the volume and
capacity of the system shall be installed.
(ii) If the system is designed for a working pressure
of 30 psig (207 kilopascals) or less, the tank shall be suitably designed
for a minimum hydrostatic pressure of 75 psig (520 kilopascals).
(iii) Expansion tanks for systems designed to operate
above 30 psig (207 kilopascals) shall be constructed in accordance
with the ASME Code, Section VIII, Division 1, or Section X, and the
pressure and temperature ratings of the tank shall be equal to or
greater than the pressure and temperature ratings of the system pressure.
A pressure relief valve shall be installed with a set pressure at
or below the MAWP of the expansion tank. Alternately the boiler pressure
relief valve may be used provided the expansion tank's MAWP is equal
to or greater than the set pressure of the pressure relief valve.
(iv) Provisions shall be made for draining the tank
without emptying the system, except for pre-pressurized tanks.
(v) If the expansion tank was originally equipped with
a sight glass, the sight glass and sight glass valves shall be in
working condition at all times, and the water level shall be maintained
as per the manufacturer's recommendations.
(8) Piping, Fittings and Valves.
(A) All piping, fittings and valves on the boiler supply
and return lines shall have a pressure rating equal to or greater
than the MAWP of the boiler and a temperature rating of no less than
250 degrees Fahrenheit (121 degrees Celsius).
(B) All piping, fittings and valves other than the
boiler supply and return lines shall have a minimum pressure and temperature
rating equal to or greater than the maximum expected pressure and
temperature that may be reached.
(c) Hot Water Supply Boilers.
(1) Pressure relief valves.
(A) Each hot water supply boiler shall have at least
one pressure relief valve, of the automatic reseating type, identified
with the ASME certification mark with the "V" or "HV" designators,
and set to relieve at or below the MAWP of the boiler.
(B) When more than one pressure relief valve is used
on a hot water supply boiler, the additional valve or valves shall
be officially rated and may have a set pressure within a range not
to exceed 6 psig (42 kilopascals) above the MAWP of the boiler up
to and including 60 psig (414 kilopascals), and 5.0% for those having
a MAWP exceeding 60 psig (414 kilopascals).
(C) Pressure relief valves shall be spring loaded.
Pressure relief valves shall be set and sealed so that they cannot
be reset without breaking the seal. A body drain connection below
seat level shall be provided. For valves exceeding 2 1/2 inch nominal
pipe size (65 mm), the drain hole or holes shall be tapped not less
than 3/8 inch nominal pipe size (10 mm). For valves of 2 1/2 inch
nominal pipe size (65 mm) or less, the drain hole shall not be less
than 1/4 inch (6 mm) diameter.
(D) Each pressure relief valve shall have a substantial
lifting device which will positively lift the disk from its seat at
least 1/16 inch (1.6 mm) when there is no pressure on the boiler.
(E) Seats and disks of pressure relief valves shall
be made of a suitable material to resist corrosion. No materials likely
to fail due to deterioration or vulcanization, when subjected to saturated
steam temperature corresponding to capacity test pressure, shall be
used for any part.
(F) No pressure relief valve shall be smaller than
3/4 inch nominal pipe size (20 mm) nor larger than 4 1/2 inch nominal
pipe size (115 mm) except that boilers having a heat input not greater
than 15,000 Btu/hr (4.4 kilowatts) may be equipped with a rated pressure
relief valve of 1/2 inch nominal pipe size (15 mm). The inlet opening
shall have an inside diameter approximately equal to, or greater than,
the seat diameter. In no case shall the minimum opening through any
part of the valve be less than 1/4 inch (6 mm) diameter or its equivalent
area.
(G) The required steam relieving capacity, in pounds
per hour, of the pressure relieving device or devices on a boiler
shall be the greater of that determined by dividing the maximum output
in Btu at the boiler nozzle obtained by the firing of any fuel for
which the unit is installed by 1,000, or shall be determined on the
basis of pounds of steam generated per hour per square foot of boiler
heating surface as given in §65.615, Exhibit 7. For cast iron
boilers, the minimum valve capacity shall be determined by the maximum
output method.
(H) In every case, the pressure relief valve capacity
for each boiler with a single pressure relief valve shall be such
that, with the fuel burning equipment installed and operated at maximum
capacity, the pressure cannot rise more than 10% above the MAWP. When
more than one pressure relief valve is used, the overpressure shall
be limited to 10% above the set pressure of the highest set valve.
(I) Pressure relief valve piping. No valve shall be
placed between the pressure relief valve and the boiler nor on the
discharge pipe between the pressure relief valve and the drain. When
a discharge pipe is used, it shall be full size and fitted with an
open drain to prevent water from lodging in the upper part of the
pressure relief valve or in the discharge pipe. When an elbow is placed
on the pressure relief valve discharge pipe, it shall be located close
to the valve outlet. The discharge pipe shall be securely anchored
and supported, independent of the valve. Mufflers shall not be used
on hot water supply boilers.
(J) Pressure relief valves and safety valves shall
be installed on the boiler with spindles positioned vertically. The
opening or connection between the boiler and any pressure relief valve
or safety valve shall have at least the area of the valve inlet.
(2) Makeup water connections.
(A) Makeup water or water treatment shall be introduced
into a boiler through the return piping system or through an independent
makeup water connection which does not discharge against parts of
the boiler exposed to direct radiant heat from the fire. Makeup water
or water treatment shall not be introduced through openings or connections
provided for inspection or cleaning, pressure relief valve, pressure
gage, or temperature gage.
(B) Makeup water pipe shall be provided with a check
valve near the boiler and a stop valve or cock between the check valve
and the boiler or between the check valve and the piping system.
(3) Low-water fuel cutoffs and water feeding devices.
(A) All automatically fired hot water supply boilers
shall have an automatic low-water fuel cutoff that has been designed
for hot water service, and it shall be so located as to automatically
cut off the fuel supply when the surface of the water falls to a level
below the normal waterline established.
(B) The MAWP of all low water fuel cutoff and flow
sensing devices shall be set at or above the boiler stamped MAWP.
(C) When low-water fuel cutoff and feedwater pump controls
are combined in a single device, an additional separate low-water
fuel cutoff shall be installed. The additional control shall be wired
in series electrically with the existing low-water fuel cutoff.
Cont'd... |
