| (D) When a low-water fuel cutoff is housed in either
the water column or a separate chamber it shall be provided with a
blowdown pipe and valve not less than 3/4 inch nominal pipe size (20
mm). The arrangement shall be such that when the water column is blown
down, the water level in it will be lowered sufficiently to activate
the low-water fuel cutoff device.
(E) As there is no normal water line to be maintained
in a hot water supply boiler, any location of the low-water fuel cutoff
above the lowest safe water level established by the boiler manufacturer
is satisfactory.
(F) All automatically fired hot water heating boilers,
when installed in a forced circulation system and not under continuous
attendance, shall be equipped in the manner described in this subsection.
A coil-type boiler or a water-tube boiler requiring forced circulation
to prevent overheating of the coils or tubes shall have a flow sensing
device which is listed by a nationally recognized testing agency to
prevent burner operation at a flow rate inadequate to protect the
boiler unit against overheating.
(G) If a water feed device is utilized, it shall be
constructed to prevent feedwater from entering the boiler through
the water column or separate chamber of the low-water fuel cutoff.
(4) Pressure and Temperature gages.
(A) Each hot water supply boiler shall have a pressure
or altitude gage connected to it or to its flow connection which cannot
be shut off from the boiler except by a cock with tee or lever handle
placed in a pipe near the gage. The handle of the cock shall be parallel
to the pipe in which it is located when the cock is open.
(B) The scale on the dial of the pressure or altitude
gage shall be graduated to not less than 1 1/2 nor more than 3 1/2
times the pressure at which the pressure relief valve is set. The
gage shall be provided with effective stops for the indicating pointer
at the zero point and at the maximum pressure point.
(C) Piping and tubing for pressure or altitude gage
connections shall be of nonferrous metal when smaller than 1 inch
nominal pipe size (25 mm).
(D) Each hot water supply boiler shall have a thermometer
or temperature gage located and connected so that it shall be readable,
and shall be located so that it shall at all times indicate the temperature
of the water in the boiler at or near the outlet. If placed on the
outlet piping, it must be located between the stop valve and the boiler.
(5) Stop valves.
(A) Stop valves shall be located at an accessible point
in the supply and return pipe connections near the boiler nozzle of
a single hot water supply boiler installation to permit draining the
boiler without emptying the system.
(B) When the boiler is located above the system and
can be drained without draining the system, stop valves may be eliminated.
(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 supply 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) If a system is equipped with a check valve or pressure
reducing valve in the cold water inlet line, consideration should
be given to the installation of an airtight expansion tank or other
suitable air cushion. Otherwise, due to the thermal expansion of the
water, the pressure relief valve may lift periodically.
(B) If an expansion tank is provided, it 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. Except for pre-pressurized tanks, which should be installed
on the cold water side, provisions shall be made for draining the
tank without emptying the system.
(C) 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.
(d) Potable Water Heaters (ASME Code HLW).
(1) Pressure relief valves.
(A) Potable water heaters (tank type) shall have at
least one officially rated temperature and pressure relief valve,
or one officially rated pressure relief valve, set to relieve at or
below the maximum allowable pressure of the heater. No pressure relief
valve shall be smaller than 3/4 inch nominal pipe size (20 mm). The
valve (s) shall be marked with the ASME Code Symbol "V" or "HV". At
no time shall the temperature probe of the temperature and pressure
relief valve be removed or modified.
(B) The pressure relief valve shall have a capacity
equal to or exceeding the rated burner input of the heater. The relieving
capacity for electric water heaters shall be 3,500 Btu/hr (1.0 kilowatts)
per kilowatt of input.
(C) The ASME Btu rating on the valve shall be used
to determine the relieving capacity.
(D) Pressure relief valves shall be connected directly
to the heater within the top 6 inches of the tank.
(E) Pressure relief valves may be installed vertically
or horizontally. The center line of the horizontal connection shall
be no lower than 4 inches from the top of the shell.
(F) Pressure relief valves shall not be connected to
an internal pipe in the heater, or to a cold water feed line connected
to the heater.
(G) 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 potable water heaters.
(2) Water supply.
(A) Water supply shall be introduced into a water heater
through an independent water supply connection. Water shall not be
introduced through openings or connections provided for cleaning,
pressure relief valves, drains, pressure gage or temperature gage.
(B) If the water supply pressure to a hot water heater
exceeds 75% of the set pressure of the pressure relief valve, a pressure
reducing valve is required.
(3) Flow sensing device.
(A) All automatically fired potable water heaters,
when installed in a forced circulation system and not under continuous
attendance, shall be equipped in the manner described in this subsection.
A coil-type boiler or a water-tube boiler requiring forced circulation
to prevent overheating of the coils or tubes shall have a flow sensing
device which is listed by a nationally recognized testing agency to
prevent burner operation at a flow rate inadequate to protect the
boiler unit against overheating.
(B) The MAWP of all flow sensing devices shall be set
at or above the boiler stamped MAWP.
(4) Gages.
Cont'd... |
