Fletcher’s rotary condensing engine has an eccentric hollow drum and three sliding abutment wings inside a double cylindrical shell. The animation illustrates this arrangement; the calculator separately compares inlet, condenser and local atmospheric pressures on an absolute basis.
Fletcher's Rotary Condensing Engine Interactive Calculator
Enter absolute inlet, condenser and local atmospheric pressures to calculate signed pressure differences and SI conversions. No mean effective pressure, power or condenser-performance estimate is produced.
Equation Used
- Inputs are absolute pressures in psi.
- Local atmospheric pressure is entered rather than fixed.
- The diagram uses illustrative dimensions for Fletcher’s eccentric drum and sliding wings; it does not determine valve timing.
- Steam expansion, valve timing, condensation, leakage and mechanical losses are not calculated. Pressure differences alone do not give engine torque or power.
Pressure difference is not mean effective pressure. Engine work requires an indicator diagram or a validated thermodynamic and valve-timing model.
Eccentric drum and sliding wings
Hiscox item 338 describes a hollow drum with its shaft offset from the center of a double cylindrical shell. Three slots carry slides and socketed arms that form abutment wings. A retaining ring keeps the wings against the inner shell; the source drawing does not show the ring itself. Steam enters through ports on the left and exhausts through ports on the right. The animation illustrates the eccentric drum and changing wing extension, with circular tip contact prescribed geometrically. It does not show the retaining ring’s construction, port timing or condenser operation.
Keep absolute and gauge references separate
Enter pressures on an absolute basis. Subtracting condenser absolute pressure from local atmospheric absolute pressure gives signed vacuum-gauge pressure. Subtracting condenser from inlet gives a signed boundary difference. Neither is an engine performance result.
Pressure arithmetic and conversion
DeltaP=Pin(abs)-Pcond(abs). Vacuum gauge=Patm(abs)-Pcond(abs). NIST gives 1 psi=6.894757 kPa.
These boundary-pressure differences are not mean effective pressure. Calculating MEP requires the cylinder pressure history over a complete cycle, including valve timing, expansion and exhaust behavior.
Example pressure references
At 25 psi absolute inlet, 3 psi absolute condenser and 14.7 psi absolute local atmosphere, the signed inlet-to-condenser difference is 22 psi and the vacuum relative to atmosphere is 11.7 psi. The absolute pressures convert to about 172.4 kPa and 20.7 kPa. No MEP or power follows from these figures alone.
What the pressure difference can tell you
NIST supplies the psi-to-kPa conversion used here. The two subtractions help keep absolute inlet pressure, condenser pressure and local atmospheric pressure on the same basis.
To estimate engine work or power, add steam state, cylinder geometry, valve timing and cutoff, a complete indicator pressure history, heat transfer, condensation, leakage, air-pump behavior and mechanical losses. Use measured data for the specific engine whenever possible.
Questions
Is inlet pressure minus condenser pressure the MEP?
No.
Does vacuum gauge pressure equal absolute pressure?
No. Here it is local atmospheric absolute pressure minus condenser absolute pressure.
Does this predict horsepower?
No.
References
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), page 93, item 338: Fletcher’s rotary condensing engine.
NIST Guide to the SI, Appendix B.9: 1 psi=6.894757 kPa.
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