INSTALLATION, OPERATION AND MAINTENANCE MANUAL
Easco Boiler Corp 1175 Leggett Ave Bronx, NY 1047 T: 718.378.3000 F: 718.378.4560 [email protected] easco.com
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5.7 Safety and Safety Relief Valves
Safety and safety relief valves are used to relieve excessive pressure generated within
the Boiler. The safety or safety relief valve(s) is the final line of protection against over
pressurization.
5.7.1 Safety Valves – Used for steam service, a safety valve is an automatic pressure
relieving device, actuated by the pressure generated within the Boiler and characterized
by full opening pop action.
5.7.2 Safety Relief Valves – Used for hot water service, a safety relief valve is an
automatic pressure-relieving device, actuated by the pressure generated within the
Boiler. Valves of this Type are spring loaded without full opening pop action.
5.7.3 Safety and safety relief valves should be lifted by hand on a monthly basis. They
should be under pressure test on an annual basis. Any problem whatsoever with the
valve should be referred to an ASME Authorized Repair Station.
5.8 Blow-Off
Boiler blow-off (blow-down, sometimes) is utilized to remove impurities from the
Boiler. Impurities may be either dissolved or non-dissolved. Frequency of blow-down is
dictated by water treatment program. Blow-off on Firebox Boilers is typically from a ‘T’
in the Return in the rear adjacent to the boiler inlet. In severe cases the washouts in the
mud legs (at bottom four corners) can be utilized also.
5.8.1 Low Pressure Boiler – The use of the blow-off or drain valve in a low pressure-
heating Boiler is for discharging rust colored water and sediment, which settles to the
bottom of the Boiler. Quantity and frequency of blow-down are based on water quality
and site-specific conditions. Excessive discharge is wasteful and should be avoided.
5.8.2 High Pressure Boilers – The use of the blow-off in high-pressure Boilers is to
remove concentration of dissolved and un-dissolved solids to prevent foaming and
undesirable water carry-over in the steam. The amount and blow-down frequency
depend on the severity of boiler service, amount of makeup water used and types of
chemical treatment utilized. Amount and blow-down frequency should be determined
by chemical analysis. ‘Guessing at it’ should be avoided at all cost. Blow down only
during periods of light load. On Boilers equipped with a quick opening and slow opening
valves, the quick opening valve should be opened first and shut last. The actual blow-
down should be performed with the slow opening valve.
5.9 System Design, Application and Operating – Hot Water Boilers
Excessive stresses in a Boiler can lead to leaks at flue joints and to component fatigue
due to thermal stress cycling, resulting in failure of stays and crack of tube sheets.
When the burner is at its maximum firing rate, the furnace temperature in a hot water
boiler is strongly influenced by the boiler operating pressure, or more accurately, the
saturation temperature corresponding to the operating pressure. The fire tube and shell
metal temperatures are mainly controlled by the operating boiler water temperature
regardless of burner firing rate. Thermal expansions of the flue tubes and shell are,
