Code of Maryland Regulations
Chapter 09.12.01 - Board of Boiler Rules - Heating Boiler - Existing Installation: Safety Valve

Universal Citation: MD Code Reg Heating Boiler - Existing Installation: Safety Valve

A. A steam boiler shall have at least one safety valve which is:

(1) Officially rated;

(2) Of the spring pop type; and

(3) Adjusted and sealed to discharge at a pressure not greater than 15 PSI.

B. A seal shall be attached in a manner to prevent the valve from being disassembled without breaking the seal.

C. A safety valve shall be arranged so that it cannot be reset to relieve at a pressure higher than the maximum allowable working pressure of the boiler.

D. Body Drain.

(1) The manufacturer shall provide a body drain connection below seat level.

(2) A body drain may not be plugged during or after field installation.

(3) If a valve exceeds 2 inch pipe size, the drain hole shall be tapped at least 3/8 inch pipe size.

(4) A valve less than 2 inches pipe size shall have a drain hole at least 1/4 inch in diameter.

E. Valve Size.

(1) A safety valve for a steam boiler shall be:

(a) At least 3/4 inches, unless the boiler and radiating surfaces are a self-contained unit; and

(b) Not larger than 4 1/2 inches.

(2) An inlet opening shall have an inside diameter at least equal to the seat diameter.

F. The minimum relief capacity of a valve or valves is governed by the capacity marking on the boiler.

G. Valve Capacity.

(1) Subject to the requirements of ยง H, below, the minimum valve capacity in pounds per hour is the greater of the capacity determined:

(a) By dividing the maximum BTU output at the boiler nozzle, obtained by firing any fuel for which the unit is installed, by 1,000; or

(b) In accordance with the following table:

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 7 8
Oil, gas, or pulverized fuel-fired 8 10
Waterwall Heating Surface
Hand-fired 8 8
Stoker-fired 10 12
Oil, gas, or pulverized fuel-fired 14 16


*1. When a boiler is fired only by a gas having a heat value of 200 BTU or less per cubic foot, the minimum safety valve or safety relief valve relief capacity may be determined by the value given for hand-fired boilers, above.

*2. Heating surface shall be determined in accordance with the ASME Code, Section IV, Paragraph HG-403.

(2) The minimum safety valve or safety relief valve relief capacity for an electric boiler shall be 3-1/2 pounds per hour per kilowatt input.

H. The safety valve capacity for a steam boiler shall be sufficient to ensure that when fuel burning equipment is operated at maximum capacity, the pressure cannot exceed the maximum allowable working pressure by more than 5 PSI.

I. When operating conditions change, or additional boiler heating surface is installed:

(1) Valve capacity shall be increased, if necessary, to:

(a) Meet the new conditions, and

(b) Comply with the requirements of this regulation;

(2) Provided there is no intervening valve, any additional valves required because of changed conditions may be installed on the outlet piping.

J. If there is any doubt as to the capacity of a safety valve, an accumulation test shall be conducted in accordance with the ASME Code, Section VI, Recommended Rules for the Care and Operation of Heating Boilers.

K. A valve of any type may not be placed:

(1) Between a safety valve and a boiler; or

(2) On a discharge pipe between a safety valve and the atmosphere.

L. Discharge Pipe.

(1) A discharge pipe shall be:

(a) At least full-size; and

(b) Fitted with an open drain to prevent water from lodging in the upper part of a safety valve or in the discharge pipe.

(2) If a safety valve discharge pipe has an elbow, the:

(a) Elbow shall be located near the safety valve outlet; or

(b) Discharge pipe shall be securely anchored and supported.

M. Safety valve discharges shall be located or piped so as not to endanger workers.

Disclaimer: These regulations may not be the most recent version. Maryland may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.