Steam Engine PressureVolume Diagram
Blue = theoretical maximum diagram
Red = typical indicator card (PV) plot
Mean effective pressure, p_{m}:
p_{m} (lb/in^{2}) = 
area of PV indicator card (lb/in^{2})(in^{3})
swept volume of cylinder (in^{3}) 
Indicated Horsepower, ihp:


Where:
p_{m} = mep, lb/in^{2}
L = stroke, ft
a = piston area, in^{2}
n = number of cycles per minute
33000 = ftlb/min / hp (definition) 
Brake horsepower, bhp:
bhp = ihp x mechanical efficiency (mech. eff. typically 80%  94%)
Friction horsepower, fhp:
fhp = ihp  bhp
Last tinkered with January 11, 2012 R.A.B.
