Iowa Administrative Code › Agency 875 - Labor Services Division › Boilers and Pressure Vessels › Chapter 92 - Power Boilers › Rule 875-92.7 - Safety Valves

Current through Register Vol. 47, No. 3, July 24, 2024
This rule applies to power boilers installed prior to July 1,
				  1983.
(1) The use of weighted-lever
				safety valves or safety valves having either the seat or disk of cast iron is
				prohibited. All power boilers shall have direct, springloaded, pop-type safety
				valves that conform to the construction or installation code.
(2) Each boiler shall have at least one
				safety valve. All boilers with more than 500 square feet of water heating
				surface or an electric power input of more than 1100 kilowatts shall have two
				or more safety valves.
(3) The
				safety valve or valves shall be connected to the boiler independent of any
				other steam connection and attached as close as possible to the boiler without
				unnecessary intervening pipe or fittings.
(4) No valves of any type shall be placed
				between the safety valve and the boiler If an escape pipe is used, no valve
				shall be placed between the safety valve and the atmosphere. When an escape
				pipe is used, it shall be at least full size of the safety valve discharge and
				fitted with an open drain to prevent water lodging in the upper part of the
				safety valve or escape pipe. Any elbow on an escape pipe shall be located close
				to the safety valve outlet or the escape pipe and shall be anchored and
				supported securely. All safety valve discharges shall be so located or piped as
				to be carried away from walkways or platforms. When the safety valve is vented
				to the outside atmosphere, the second escape pipe shall be arranged as shown in
				Figure 1.
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(5)
				The safety valve capacity of each boiler shall be such that the safety valve or
				valves will discharge all the steam that can be generated by the boiler without
				allowing the pressure to rise more than 5 percent above the highest pressure to
				which any valve is set and in no case to more than 6 percent above maximum
				allowable working pressure.
(6) One
				or more safety valves on every boiler shall be set at or below the maximum
				allowable working pressure. The remaining valves may be set within a range of 3
				percent above the maximum allowable working pressure, but the range setting of
				all the safety valves on a boiler shall not exceed 10 percent of the highest
				pressure at which any valve is set.
(7) When two or more boilers operating at
				different pressures and safety valve settings are interconnected, the lowest
				pressure boilers or interconnected piping shall be equipped with safety valves
				of sufficient capacity to prevent overpressure, considering the maximum
				generating capacity of all boilers.
(8) In those cases where the boiler is
				supplied with feedwater directly from water mains without the use of feeding
				apparatus (not including return traps), safety valves shall not be set at a
				pressure greater than 94 percent of the lowest pressure maintained in the
				supply main feeding the boiler.
(9)
				The minimum safety valve relieving capacity shall be determined on the basis of
				the pounds of steam generated per hour per square foot of boiler heating
				surface and waterwall heating surface as given in the following table. This
				method shall not be used on electric boilers, waste heat boilers and
				forced-flow steam generators without a fixed steam and water line.
Minimum Pounds of Steam Per Hour Per Square Foot of Heating
				  Surface
Boiler Heating Surface: Firetube Boilers Watertube
				  Boilers
Hand Fired...................................... 5 6
Stoker Fired..................................... 5 8
Oil, Gas, or Pulverized Fuel Fires...................... 8
				  10
Waterwall Heating Surface:
Hand Fired...................................... 8 8
Stoker Fired..................................... 10
				  12
Oil, Gas, or Pulverized Fuel Fires...................... 14
				  16
(10) Safety valve
				sizing.
a. When a boiler is fired only by a
				gas having a heat value not in excess of 200 Btu's per cubic feet the minimum
				safety valve relieving capacity may be based on the value given for hand-fired
				boilers above.
b. The minimum
				safety valve relieving capacity for electric boilers shall be 3/4 pounds per
				hour per kilowatt input.
c. Maximum
				steaming capacity for safety valves shall be the value stated on design
				documents or shall be calculated by multiplying horsepower by 34.5.