A 1913 Union Gas Engine Company catalog documents Union cylinders, pistons, connecting rods, crankshafts, valves and make-and-break ignition. This calculator is a generic single-cylinder power comparison using entered values; it does not reproduce or rate a particular Union engine.
Union Model Gas Engine Interactive Calculator
Enter an assumed mean indicated pressure, cylinder bore, stroke, crank speed and revolutions per power event. Results are ideal arithmetic references—not a dynamometer measurement, historical rating or operating recommendation.
Equation Used
- One entered circular cylinder bore and piston stroke.
- Entered mean indicated pressure is treated as a cycle-average net indicated value acting over the power stroke.
- Power-event rate is entered crank RPM divided by entered revolutions per power event.
- The 85% mechanical efficiency is a fixed display assumption, not a Union specification.
- Equivalent average torque is derived from the assumed shaft-power estimate and crank speed.
- Combustion, gas exchange, ignition, governor dynamics, friction variation, pumping work, heat transfer, mixture, compression ratio, measured indicator diagrams, speed fluctuation, structural loads and safety are omitted.
Documented Union Hardware and the Calculator Boundary
The Union Gas Engine Company's 1913 catalog documents water-jacketed cylinders and heads, pistons, connecting rods, crankshafts, valves and make-and-break ignition. An earlier engineering text also illustrates a Union rocking-shaft sparker.
The animation is a generic slider-crank section alongside the calculated power values. It does not reproduce the dimensions, valve timing, combustion or governor of a particular Union engine.
What This Calculator Represents
The tool converts entered bore and stroke to piston area and swept length, combines them with entered mean indicated pressure and entered power-event rate, and applies the standard indicated-horsepower relation. It then multiplies by a fixed assumed 85% mechanical efficiency solely to provide a shaft-power reference.
Indicated-Power Calculation
power-event rate N = RPM / Rf
indicated hp = P L A N / 33,000
assumed shaft hp = 0.85 × indicated hp
equivalent average torque = 5252.113 × shaft hp / RPM
NIST defines indicated horsepower from mean indicated pressure, stroke, net piston area and power strokes per minute. It separately defines brake horsepower as shaft output determined by a brake and mechanical efficiency as brake horsepower divided by indicated horsepower.
Worked Arithmetic Example
At 75 psi entered mean indicated pressure, 8 in bore, 10 in stroke, 250 RPM and one power event every 2 revolutions, piston area is 50.27 in² and event rate is 125 per minute. Indicated power is about 11.9 hp; applying the fixed 85% assumption gives about 10.1 hp (7.5 kW) and an equivalent average torque near 212 lb-ft.
Model Boundary
- Calculated: piston area, entered power-event rate, indicated horsepower, fixed-assumption shaft power and corresponding average torque.
- Illustrated: generic cylinder, piston, connecting rod, crank and flywheel.
- Not calculated: an actual Union rating, combustion, pressure trace, pumping loss, friction variation, volumetric or thermal efficiency, mixture, ignition, governor behavior, valve timing, speed ripple, cooling, structural stress, durability or safety.
Frequently Asked Questions
Is the result measured brake horsepower?
No. NIST defines brake horsepower as shaft output determined by a brake; this page applies an assumed efficiency to an indicated-power calculation.
Is 85% a documented Union efficiency?
No. It is a fixed illustrative assumption.
Does revolutions per power event prove hit-and-miss governor behavior?
No. It is only an entered event interval.
Does the animation reproduce a specific Union model?
No.
Is mean indicated pressure predicted from fuel or compression ratio?
No; it is entered directly.
Can this calculator rate or operate an antique engine?
No.
References
- Union Gas Engine Company, 1913 catalog: documented Union cylinder, piston, connecting rod, crankshaft, valve and ignition construction.
- U.S. Department of Commerce / National Bureau of Standards, Commercial Standard CS102E-42: indicated horsepower, mean indicated pressure, brake horsepower and mechanical-efficiency definitions.
- Gardner D. Hiscox, Gas, Gasoline and Oil-Engines: Union Gas Engine Company rocking-shaft sparker illustration.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
