(3) The line side of the control circuit shall be provided with a time delay fuse sized as small as practicable.
(b) Two-Wire Nominal 120 V System Obtained By Using an Isolation Transformer
(1) The two-wire control circuit shall be obtained from the secondary side of an isolation transformer. One wire from the secondary of this transformer shall be electrically continuous and shall be bonded to a convenient cold water pipe. All metallic enclosures of control components shall be securely bonded to this ground control circuit wire. The primary side of the isolation transformer will normally be a two-wire source with a potential of 230 V or 208 V or 440 V.
(2) Both sides of the two-wire primary circuit shall be fused. The hot leg on the load side of the isolation transformer shall be fused as small as practicable and in no case fused above the rating of the isolation transformer.
HG-633 LIMIT CONTROLS
Limit controls shall be wired on the hot or line side of the control circuit.
HG-634 SHUTDOWN SWITCHES AND CIRCUIT BREAKERS
A manually operated remote heating plant shutdown switch or circuit breaker should be located just outside the boiler room door and marked for easy identification. Consideration should also be given to the type and location of the switch to safeguard against tampering. If the boiler room door is on the building exterior the switch should be located just inside the door. If there is more than one door to the boiler room, there should be a switch located at each door.
(a) For atmospheric-gas burners, and oil burners where a fan is on a common shaft with the oil pump, the complete burner and controls should be shut off.
(b) For power burners with detached auxiliaries, only the fuel input supply to the firebox need be shut off.
HG-640 CONTROLS AND HEAT GENERATING APPARATUS
(a) Oil and gas-fired and electrically heated boilers should be equipped with suitable primary (flame safeguard) safety controls, safety limit switches, and burners or electric elements as required by a nationally recognized standard.
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(b)
The symbol of the certifying organization
3 that has investigated such equipment as having complied with a nationally recognized standard shall be affixed to the equipment and shall be considered as evidence that the unit was manufactured in accordance with that standard.
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ARTICLE 7
INSTALLATION REQUIREMENTS
HG-700 INSTALLATION REQUIREMENTS, ALL BOILERS
HG-701 MOUNTING SAFETY AND SAFETY RELIEF VALVES
HG-701.1 Permissible Mounting. Safety valves and safety relief valves shall be located in the top or side
1 of the boiler. They shall be connected directly to a tapped or flanged opening in the boiler, to a fitting connected to the boiler by a short nipple, to a Y-base, or to a valveless header connecting steam or water outlets on the same boiler. Coil or header type boilers shall have the safety valve or safety relief valve located on the steam or hot water outlet end. Safety valves and safety relief valves shall be installed with their spindles vertical. The opening or connection between the boiler and any safety valve or safety relief valve shall have at least the area of the valve inlet.
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HG-701.2 Requirements for Common Connections for Two or More Valves
(a) When a boiler is fitted with two or more safety valves on one connection, this connection shall have a cross-sectional area not less than the combined areas of inlet connections of all the safety valves with which it connects.
(b) When a Y-base is used, the inlet area shall be not less than the combined outlet areas. When the size of the boiler requires a safety valve or safety relief valve larger than 4½ in. (115 mm) in diameter, two or more valves having the required combined capacity shall be used. When two or more valves are used on a boiler, they may be single, directly attached, or mounted on a Y-base.
HG-701.3 Threaded Connections. A threaded connection may be used for attaching a valve.
HG-701.4 Prohibited Mountings. Safety and safety relief valves shall not be connected to an internal pipe in the boiler.
HG-701.5 Use of Shutoff Valves Prohibited. No shutoff of any description shall be placed between the safety or safety relief valve and the boiler, or on discharge pipes between such valves and the atmosphere.
HG-701.6 Safety and Safety Relief Valve Discharge Piping
(a) A discharge pipe shall be used. Its internal cross-sectional area shall be not less than the full area of the valve outlet or of the total of the valve outlets discharging thereinto and shall be as short and straight as possible and so arranged as to avoid undue stress on the valve or valves. A union may be installed in the discharge piping close to the valve outlet. When an elbow is placed on a safety or safety relief valve discharge pipe, it shall be located close to the valve outlet downstream of the union.
(b) The discharge from safety or safety relief valves shall be so arranged that there will be no danger of scalding attendants. The safety or safety relief valve discharge shall be piped away from the boiler to the point of discharge, and there shall be provisions made for properly draining the piping. The size and arrangement of discharge piping shall be independent of other discharge piping and shall be such that any pressure that may exist or develop will not reduce the relieving capacity of the relieving devices below that required to protect the boiler.
HG-701.7 Temperature and Pressure Safety Relief Valves. Hot water heating or supply boilers limited to a water temperature of 210°F (99°C) may have one or more officially rated temperature and pressure safety relief valves installed. The requirements of HG-701.1 through HG-701.6 shall be met, except as follows:
(a) A Y-type fitting shall not be used.
(b) If additional valves are used they shall be temperature and pressure safety relief valves.
(c) When the temperature and pressure safety relief valve is mounted directly on the boiler with no more than 4 in. (100 mm) maximum interconnecting piping, the valve may be installed in the horizontal position with the outlet pointed down.
HG-703.1 Provisions for Expansion and Contraction. Provisions shall be made for the expansion and contraction of steam and hot water mains connected to boilers by providing substantial anchorage at suitable points and by providing swing joints when boilers are installed in batteries, so there will be no undue strain transmitted to the boilers. See Figs. HG-703.1(a), HG-703.1(b), and HG-703.2 for typical schematic arrangements of piping incorporating strain absorbing joints for steam and hot water heating boilers.
HG-703.2 Return Pipe Connections
(a) The return pipe connections of each boiler supplying a gravity return steam heating system shall be so arranged as to form a loop substantially as shown in Fig. HG-703.l(b) so that the water in each boiler cannot be forced out below the safe water level.
(b) For hand-fired boilers with a normal grate line, the recommended pipe sizes detailed as “A" in Fig. HG-703.1 are NPS 1½ (DN 40) for 4 ft2 (0.37 m2) or less firebox area at the normal grate line, NPS 2½ (DN 65) for areas more than 4 ft2 (0.37 m2) up to 14.9 ft2 (1.4 m2), and NPS 4 (DN 100) for 15 ft2 (1.4 m2) or more.
(c) For automatically fired boilers that do not have a normal grate line, the recommended pipe sizes detailed as “A" in Fig. HG-703.1 are NPS 1½ (DN 40) for boilers with minimum safety valve relieving capacity 250 lb/hr (113 kg/hr) or less, NPS 2½
(DN 65) for boilers with minimum safety valve relieving capacity from 251 lb/hr (114 kg/hr) to 2,000 lb/hr (900 kg/hr), inclusive, and NPS 4 (DN 100) for boilers with more than 2,000 lb/hr (900 kg/hr) minimum safety valve relieving capacity.
(d) Provision shall be made for cleaning the interior of the return piping at or close to the boiler. Washout openings may be used for return pipe connections and the washout plug placed in a tee or a cross so that the plug is directly opposite and as close as possible to the opening in the boiler.
HG-705 FEEDWATER AND MAKEUP WATER
CONNECTIONS
(a) Steam Boilers. Feedwater or water treatment shall be introduced into a boiler through the return piping system. Alternatively, feedwater or water treatment may be introduced through an independent connection. The water flow from the independent connection shall not discharge directly against parts of the boiler exposed to direct radiant heat from the fire. Feedwater or water treatment shall not be introduced through openings or connections provided for inspection or cleaning, safety valve, water column, water gage glass, or pressure gage. The feedwater pipe shall be provided with a check valve or a backflow preventer containing a check valve3 near the boiler and a stop valve or cock between the check valve and the boiler or between the check valve and the return pipe system.
(b)
Hot Water Boilers. Makeup water may be introduced into a boiler through the piping system or through an independent connection. The water flow from the independent connection shall not discharge directly against parts of the boiler exposed to direct radiant heat from the fire. Makeup water shall not be introduced through openings or connections provided exclusively for inspection or cleaning, safety relief valve, pressure gage, or temperature gage. The makeup water pipe shall be provided with a check valve or a backflow preventer containing a check valve
3 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.
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HG-707 OIL HEATERS
(a) A heater for oil or other liquid harmful to boiler operation shall not be installed directly in the steam or water space within a boiler.
(b) Where an external type heater for such service is used, means shall be provided to prevent the introduction into the boiler of oil or other liquid harmful to boiler operation.
HG-708 STORAGE TANKS FOR HOT WATER
SUPPLY SYSTEMS
If a system is to utilize a storage tank that exceeds the capacity exception of HLW-101.2 (c), the tank shall be constructed in accordance with the rules of Part HLW; Section VIII, Division 1; or Section X. For tanks constructed to Section X, the maximum allowable temperature marked on the tank shall equal or exceed the maximum water temperature marked on the boiler.
HG-709 PROVISIONS FOR THERMAL
EXPANSION IN HOT WATER SYSTEMS
All hot water heating systems incorporating hot water tanks or fluid relief columns shall be so installed as to prevent freezing under normal operating conditions.
HG-709.1 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 the basement.
HG-709.2 Closed Heating Systems. An expansion tank shall be installed that will be consistent with the volume and capacity of the system. If the system is designed for a working pressure of 30 psi (200 kPa) or less, the tank shall be suitably designed for a minimum hydrostatic test pressure of 75 psi (520 kPa). Expansion tanks for systems designed to operate above 30 psi (200 kPa) shall be constructed in accordance with Section VIII, Division 1. Alternatively, a tank built to Section X requirements may be used if the pressure and temperature ratings of the tank are equal to or greater than the pressure and temperature ratings of the system. Provisions shall be made for draining the tank without emptying the system, except for prepressurized tanks.
The minimum capacity of the closed type expansion tank may be determined from Table HG-709.2 or from the following formula where the necessary information is available:
(U.S. Customary Units)
Vt = [(0.00041T - 0.0466)Vs ]/[(Pa/Pf) - (Pa/Po)]
(SI Units)
Vt = [(0.18155T – 8.236)Vs ]/[(Pa/Pf) - (Pa/Po)]
where
Pa = atmospheric pressure
Pf = fill pressure
Po = maximum operating pressure
T = average operating temperature
Vs = volume of system, not including tanks
HG-709.3 Hot Water Supply Systems. 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 safety relief valve may lift periodically. If an expansion tank is provided, it shall be constructed in accordance with Section VIII, Division 1 or Section X. Except for prepressurized tanks, which should be installed on the cold water side, provisions shall be made for draining the tank without emptying the system. See Fig. HLW-809.1 for a typical acceptable installation.
HG-710 STOP VALVES
HG-710.1 For Single Steam Boilers. When a stop valve is used in the supply pipe connection of a single steam boiler, there shall be one used in the return pipe connection.
HG-710.2 For Single Hot Water Heating Boilers
(a) Stop valves shall be located at an accessible point in the supply and return pipe connections as near the boiler nozzle as is convenient and practicable, of a single hot water heating 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.
HG-710.3 For Multiple Boiler Installations. A stop valve shall be used in each supply and return pipe connection of two or more boilers connected to a common system. See Figs. HG-703.1 and HG-703.2.
HG-710.4 Type of Stop Valve(s)
(a) All valves or cocks shall conform with the applicable portions of HF-203 and may be ferrous or nonferrous.
(b) The minimum pressure rating of all valves or cocks shall be at least equal to the pressure stamped upon the boiler, and the temperature rating of such valves or cocks, including all internal components, shall be not less than 250°F (120
°C).
(c) Valves or cocks shall be flanged, threaded, or have ends suitable for welding or brazing.
(d) All valves or cocks with stems or spindles shall have adjustable pressure type packing glands and, in addition, all plug type cocks shall be equipped with a guard or gland. The plug or other operating mechanism shall be distinctly marked in line with the passage to indicate whether it is opened or closed.
(e) All valves or cocks shall have tight closure when under boiler hydrostatic test pressure.
HG-710.5 Identification of Stop Valves by Tags. When stop valves are used, they shall be properly designated substantially as follows by tags of metal or other durable material fastened to them:
