P99 LOW PRESSURE BOILERS:
CHAPTER 2 EXAM SIMPLIFIED
REVISION SUMMARY
Safety Valve
An automatic, full-opening, pop-action valve, opened by
overpressure before damage occurs.
Chattering
The rapid opening and closing of the safety valve.
Safety Valve Capacity
The amount of steam, in pounds per hour, that the safety
valve is capable of venting at the rated pressure of the
safety valve.
Area of the valve disc
Area = 0.7854 * Diameter Squared
Total Force
The total amount of force in pounds acting against the
safety valve disc.
Total Force Equation
(TF=P*A) Total Force = Pressure times Area
Huddling Chamber
A recessed area in the safety valve disc that increases the
surface area and total force applied when the valve opens.
Blowback
The drop in pressure in the boiler that occurs after the
safety valve has opened.
Boilers with more than 500 sq ft of heating surface
, These must have two or more safety valves according to
ASME Boiler and Pressure Vessel Code.
Safety Relief Valves
A special design of an automatic valve that can be used
as a safety valve or as a relief valve, depending on
application.
Try Lever Test
A safety valve test performed by lifting the safety valve try
lever.
Every 30 Days of Operation or After a Period of
Inactivity
The ASME Boiler and Pressure Vessel Code Section IV,
Recommended Rules for Care and Operation of Heating
Boilers rule for how often a Try Lever Test should be
performed.
5-10 Seconds
The low pressure boiler, with a minimum of 5 psi, required
time wide open for a try lever test.
Pop Test
A safety valve test performed to determine if a safety valve
opens at the proper pressure within allowable tolerances.
Two qualified persons
The minimum number of people required to perform a pop
test.
Annually
The ASME Boiler and Pressure Vessel Code Section VI,
Recommended Rules for Care and Operation of Heating
Boilers requirement for when a Pop Test should be
performed. It can be required more often with
recommendation of the boiler inspector.
CHAPTER 2 EXAM SIMPLIFIED
REVISION SUMMARY
Safety Valve
An automatic, full-opening, pop-action valve, opened by
overpressure before damage occurs.
Chattering
The rapid opening and closing of the safety valve.
Safety Valve Capacity
The amount of steam, in pounds per hour, that the safety
valve is capable of venting at the rated pressure of the
safety valve.
Area of the valve disc
Area = 0.7854 * Diameter Squared
Total Force
The total amount of force in pounds acting against the
safety valve disc.
Total Force Equation
(TF=P*A) Total Force = Pressure times Area
Huddling Chamber
A recessed area in the safety valve disc that increases the
surface area and total force applied when the valve opens.
Blowback
The drop in pressure in the boiler that occurs after the
safety valve has opened.
Boilers with more than 500 sq ft of heating surface
, These must have two or more safety valves according to
ASME Boiler and Pressure Vessel Code.
Safety Relief Valves
A special design of an automatic valve that can be used
as a safety valve or as a relief valve, depending on
application.
Try Lever Test
A safety valve test performed by lifting the safety valve try
lever.
Every 30 Days of Operation or After a Period of
Inactivity
The ASME Boiler and Pressure Vessel Code Section IV,
Recommended Rules for Care and Operation of Heating
Boilers rule for how often a Try Lever Test should be
performed.
5-10 Seconds
The low pressure boiler, with a minimum of 5 psi, required
time wide open for a try lever test.
Pop Test
A safety valve test performed to determine if a safety valve
opens at the proper pressure within allowable tolerances.
Two qualified persons
The minimum number of people required to perform a pop
test.
Annually
The ASME Boiler and Pressure Vessel Code Section VI,
Recommended Rules for Care and Operation of Heating
Boilers requirement for when a Pop Test should be
performed. It can be required more often with
recommendation of the boiler inspector.
