Page 114 - 2018_IMC

BOILERS, WATER HEATERS AND PRESSURE VESSELS

1006.6 Safety and relief valve discharge. Safety and relief lation of water through the boiler and that are protected
valve discharge pipes shall be of rigid pipe that is approved with a flow sensing control.
for the temperature of the system. High-pressure-steam safety 1007.2 Operation. Low-water cutoff controls and flow sens-
valves shall be vented to the outside of the structure. The dis- ing controls required by Section 1007.1 shall automatically
charge piping serving pressure relief valves, temperature stop the combustion operation of the appliance when the
relief valves and combinations of such valves shall: water level drops below the lowest safe water level as estab-
1. Not be directly connected to the drainage system. lished by the manufacturer or when water circulation stops,
respectively.
2. Discharge through an air break located in the same
room as the appliance.
3. Not be smaller than the diameter of the outlet of the SECTION 1008
valve served and shall discharge full size to the air BOTTOM BLOWOFF VALVE
break.
1008.1 General. Steam boilers shall be equipped with bottom
4. Serve a single relief device and shall not connect to blowoff valve(s). The valve(s) shall be installed in the open-
piping serving any other relief device or equipment. ing provided on the boiler. The minimum size of the valve(s)
5. Discharge to the floor, to the pan serving the boiler or and associated piping shall be the size specified by the boiler
storage tank, to a waste receptor or to the outdoors. manufacturer or the size of the boiler blowoff-valve opening.
Where the maximum allowable working pressure of the
6. Discharge in a manner that does not cause personal
injury or structural damage. boiler exceeds 100 psig (689 kPa), two bottom blowoff
valves shall be provided consisting of either two slow-open-
7. Discharge to a termination point that is readily ing valves in series or one quick-opening valve and one slow-
observable by the building occupants. opening valve in series, with the quick-opening valve
8. Not be trapped. installed closest to the boiler.
9. Be installed so as to flow by gravity. 1008.2 Discharge. Blowoff valves shall discharge to a safe
place of disposal. Where discharging to the drainage system,
10. Not terminate more than 6 inches (152 mm) above the the installation shall conform to the International Plumbing
floor or waste receptor.
Code.
11. Not have a threaded connection at the end of such pip-
ing.
12. Not have valves or tee fittings. SECTION 1009
13. Be constructed of those materials listed in Section HOT WATER BOILER EXPANSION TANK
605.4 of the International Plumbing Code or materi- 1009.1 Where required. An expansion tank shall be
als tested, rated and approved for such use in accor- installed in every hot water system. For multiple boiler instal-
dance with ASME A112.4.1. lations, not less than one expansion tank is required. Expan-
1006.7 Boiler safety devices. Boilers shall be equipped with sion tanks shall be of the closed or open type. Tanks shall be
controls and limit devices as required by the manufacturer’s rated for the pressure of the hot water system.
installation instructions and the conditions of the listing. Exception: Expansion tanks shall not be required in the
1006.8 Electrical requirements. The power supply to the collector loop of drain-back systems.
electrical control system shall be from a two-wire branch cir- 1009.2 Closed-type expansion tanks. Closed-type expan-
cuit that has a grounded conductor, or from an isolation trans- sion tanks shall be installed in accordance with the manufac-
former with a two-wire secondary. Where an isolation turer’s instructions. Expansion tanks for systems designed to
transformer is provided, one conductor of the secondary have an operating pressure in excess of 30 psi (207 kPa) shall
winding shall be grounded. Control voltage shall not exceed be constructed and certified in accordance with the ASME
150 volts nominal, line to line. Control and limit devices shall Boiler and Pressure Vessel Code. The size of the tank shall
interrupt the ungrounded side of the circuit. A means of man- be based on the capacity of the hot-water-heating system. The
ually disconnecting the control circuit shall be provided and minimum size of the tank shall be determined in accordance
controls shall be arranged so that when deenergized, the with the following equation where all necessary information
burner shall be inoperative. Such disconnecting means shall is known:
be capable of being locked in the off position and shall be ( 0.00041T – 0.0466) V
provided with ready access. V = -------------------------------------------------------- s (Equation 10-1)
t
 P a  P a
-----
 ----- –  P  o
P 
f
SECTION 1007
BOILER LOW-WATER CUTOFF
1007.1 General. Steam and hot water boilers shall be pro-
tected with a low-water cutoff control.
Exception: A low-water cutoff is not required for coil-
type and water-tube-type boilers that require forced circu-

2018 INTERNATIONAL MECHANICAL CODE  97
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