Formulas and constants used for the DC 3rd class boiler exam
DC Boiler Exam Prep 2023 (Formulas and constants used
for the DC 3rd class boiler exam)
Area of a rectangle Length x Width
Area of a Circle .7854 x Diameter²
Volume of a Box Length x Width x Height
Volume of a Cylinder .7854 x Diameter² x Length
Circumference of a Circle π x Diameter
Unit of Force Pound (lb)
Formula for Force Pressure ÷ Area
Unit of Work in-lb or ft-lb
Formula for Work Force x Distance
Unit of Power ft-lb/min
Formula for Power = Work ÷ Time
or (Force x Distance) ÷ Time
Formula for Mechanical Horsepower = Power ÷ 33,000 ft-lb/min
Fahrenheit to Celsius °C = (°F - 32) ÷ 1.8
Celsius to Fahrenheit °F = (1.8 x °C) - 32
Fahrenheit to Rankine °R = °F + 460
Celsius to Kelvin K = °C +273.15
Charles' First Law Volume1 / Pressure1 = Volume2 / Pressure2
Charles' Second Law Pressure1 / Temperature1 = Pressure2 / Temperature2
Boyle's Law Pressure1 x Volume1 = Pressure2 x Volume2
General Gas Law (Pres1 x Vol1)/ Temp1 = (Pres2 x Vol2)/Temp2
Formula for Levers Resistance x DistanceR = Effort x DistanceE
Formula for Inclined Planes Force x Length = Resistance x Height
, Formula for Wheel & Axel Force x DistanceF = Resistance x DistanceR
Torque Force x Radius
Safe Working Pressure of a Riveted Boiler (SWP) (Area of Staybolt x Stress Constant of
Staybolt) ÷ Area Covered by Staybolt or = (a x C) ÷ A
Area Covered by Staybolt = Pitch x Pitch
Longitudinal Stress (P x D x L) / 2t
P = Pressure
D = Diameter
L = Length
t = thickness of steel
Boiler Heating Surface (tubes) = =CxLx#
C = Circumference of tubes
L = Length of tubes
# = Number of tubes
HS = π x Diameter x Length x Number of Tubes
Watts per Boiler Horsepower 746 Watts
Horsepower formula = ft-lb/min ÷ 33000 ft-lb/min
ft-lb formula for a pump = gpm x 8.33 x head (ft)
Factor of Evaporation (FE) = = [Hs - (tfw-32)] ÷ 970.3
Hs = Enthalpy of steam
tfw = temperature of feed water
Latent Heat of Vaporization for Water 970.3 Btu/lb
Latent Heat of Fusion for Water 144 Btu/lb
1 Boiler Horsepower = x lbs of steam generator per hour 34.5 lbs/hr
1 Boiler Horsepower = x Btu/hr 33,475 Btu/hr
1 BHP = x ft² of heating surface (general) 10 ft² heating surface
Volume of water increases by x percent when it flashes to steam x 1600
Thermal Efficiency (TE) = = Lbs Steam per hour [Hs -(fwt° -32)] ÷ Units of Fuel per hour
x Btu content per unit of fuel
Hs = Btu content of steam
fwt = feed water temperature
Developed Boiler Horsepower (DBHP) = = (Pounds of Steam per hour (Ws) x FE) ÷ 34.5
Ws = Lbs of steam per hour
DC Boiler Exam Prep 2023 (Formulas and constants used
for the DC 3rd class boiler exam)
Area of a rectangle Length x Width
Area of a Circle .7854 x Diameter²
Volume of a Box Length x Width x Height
Volume of a Cylinder .7854 x Diameter² x Length
Circumference of a Circle π x Diameter
Unit of Force Pound (lb)
Formula for Force Pressure ÷ Area
Unit of Work in-lb or ft-lb
Formula for Work Force x Distance
Unit of Power ft-lb/min
Formula for Power = Work ÷ Time
or (Force x Distance) ÷ Time
Formula for Mechanical Horsepower = Power ÷ 33,000 ft-lb/min
Fahrenheit to Celsius °C = (°F - 32) ÷ 1.8
Celsius to Fahrenheit °F = (1.8 x °C) - 32
Fahrenheit to Rankine °R = °F + 460
Celsius to Kelvin K = °C +273.15
Charles' First Law Volume1 / Pressure1 = Volume2 / Pressure2
Charles' Second Law Pressure1 / Temperature1 = Pressure2 / Temperature2
Boyle's Law Pressure1 x Volume1 = Pressure2 x Volume2
General Gas Law (Pres1 x Vol1)/ Temp1 = (Pres2 x Vol2)/Temp2
Formula for Levers Resistance x DistanceR = Effort x DistanceE
Formula for Inclined Planes Force x Length = Resistance x Height
, Formula for Wheel & Axel Force x DistanceF = Resistance x DistanceR
Torque Force x Radius
Safe Working Pressure of a Riveted Boiler (SWP) (Area of Staybolt x Stress Constant of
Staybolt) ÷ Area Covered by Staybolt or = (a x C) ÷ A
Area Covered by Staybolt = Pitch x Pitch
Longitudinal Stress (P x D x L) / 2t
P = Pressure
D = Diameter
L = Length
t = thickness of steel
Boiler Heating Surface (tubes) = =CxLx#
C = Circumference of tubes
L = Length of tubes
# = Number of tubes
HS = π x Diameter x Length x Number of Tubes
Watts per Boiler Horsepower 746 Watts
Horsepower formula = ft-lb/min ÷ 33000 ft-lb/min
ft-lb formula for a pump = gpm x 8.33 x head (ft)
Factor of Evaporation (FE) = = [Hs - (tfw-32)] ÷ 970.3
Hs = Enthalpy of steam
tfw = temperature of feed water
Latent Heat of Vaporization for Water 970.3 Btu/lb
Latent Heat of Fusion for Water 144 Btu/lb
1 Boiler Horsepower = x lbs of steam generator per hour 34.5 lbs/hr
1 Boiler Horsepower = x Btu/hr 33,475 Btu/hr
1 BHP = x ft² of heating surface (general) 10 ft² heating surface
Volume of water increases by x percent when it flashes to steam x 1600
Thermal Efficiency (TE) = = Lbs Steam per hour [Hs -(fwt° -32)] ÷ Units of Fuel per hour
x Btu content per unit of fuel
Hs = Btu content of steam
fwt = feed water temperature
Developed Boiler Horsepower (DBHP) = = (Pounds of Steam per hour (Ws) x FE) ÷ 34.5
Ws = Lbs of steam per hour
