A direct-connected vertical compound engine has vertically arranged steam cylinders driving a crankshaft connected directly to a generator. The same shaft speed reaches the generator without an intervening belt or gear ratio.
The cutaway shows an HP cylinder, an LP cylinder, crossheads, rigid connecting rods, phased cranks and a generator on the common shaft. Its calculator compares cylinder swept volumes, area ratio, rod length, shaft speed and crank phase. It does not infer electrical power or steam economy from those dimensions.
Direct-connected Vertical Compound Engine Interactive Calculator
Explore two vertical cylinder stages and a generator on one shaft. Adjust bores, common stroke, rod ratio and crank phase; piston and rotor motion stay mechanically synchronized.
Equation Used
- Two vertical cylinders with equal stroke and rigid guided crossheads.
- Fixed rod ratio and selected crank phase on one shared shaft.
- Full-bore head-side geometric swept volume; no rod-area or clearance correction.
- No pressure cycle, valve timing, torque, efficiency or electrical-power prediction.
Two vertical cylinders drive a common shaft and generator. Internal proportions are illustrative. Full-bore swept volumes describe cylinder geometry; steam consumption, power and valve timing require additional data.
Two cylinder stages, one directly connected shaft
The smaller high-pressure stage normally receives boiler steam. Its exhaust passes through a receiver or passage to the low-pressure stage before leaving toward the final exhaust. The staged steam route is shown separately from the moving linkage; individual valves and pressure cycles are not simulated.
In the cutaway, each piston and crosshead stay on a fixed vertical axis. The connecting rod swings between the crosshead and a rotating crank pin. Both cranks turn at the same shaft speed, with the selected constant phase difference. The generator rotor turns with that same shaft.
The two-cylinder, equal-stroke arrangement illustrates the direct-connected compound-engine principle. Hiscox figure 718 documents the vertical engine beside its directly connected multipolar dynamo. The internal dimensions, crank phase and section details here are modeling choices, not a claim to reproduce the exact pictured machine.
Using the geometry comparison
Adjust each bore to see the physical cylinder sizes and full-bore swept volumes change. Common stroke changes piston travel and crank radius. Rod ratio changes rod length and motion between the two dead centers. Crank phase changes how the pistons move relative to one another.
The LP/HP area ratio is useful for describing the geometry, but it is not a thermal efficiency or total steam-expansion ratio. If the selected LP bore is smaller than the HP bore, the diagram remains available and explicitly notes that this is a geometric comparison rather than the usual larger-LP arrangement.
Swept volume and exact crank closure
For bore D and stroke S, full-bore swept volume per stroke is V=πD²S/4. This is the cylinder’s head-side geometric displacement; piston-rod area, clearance volume and valve cutoff are not included. The LP/HP area ratio is (DLP/DHP)².
r=S/2; L=r×rod ratio
With a crank pin at transverse coordinate r cosθ and height r sinθ relative to the crankshaft, the crosshead height is z=r sinθ+√(L²−r²cos²θ). Adding the fixed piston-rod length gives the piston position. The same exact relation is used for each cylinder at its own crank angle.
θLP=θHP+φ; generator rpm=crankshaft rpm
The selected phase fixes the angular separation between the two cranks. This calculator does not solve valve timing, indicated work, receiver pressure, balancing or torsional vibration.
Default dimensions
A 9 inch HP bore and 16 inch LP bore with a common 12 inch stroke give about 763.41 in³ and 2,412.74 in³ full-bore swept volume per stroke. Their area ratio is 3.16. A rod ratio of four gives a 24 inch connecting rod from crank pin to crosshead.
With a 90° phase lead, the LP crank remains one quarter-turn ahead of the HP crank. At 200 rpm the generator also turns at 200 rpm. Electrical power cannot be calculated without the steam cycle, mechanical losses and generator characteristics.
What is and is not calculated
The display uses rigid rods, fixed guides, a common stroke and constant-speed shaft rotation. Cylinder bore and stroke are dimensional inputs. Frame, crank webs, piston rods, generator housing and poles are illustrative proportions, with no manufacturing or collision-clearance certification.
The steam-route diagram is an operating-principle overview, not a timed valve or mass-flow model. The animation does not assign constant colored pressures to moving chambers or imply a specific cutoff schedule. Swept volume is not steam consumption.
To evaluate a working engine, combine the cylinder geometry with steam pressures, cutoff timing, losses, balancing requirements and generator characteristics.
Playback is slowed for inspection. Zero rpm stops autoplay but leaves the geometry available for scrubbing. No force, power, fatigue or operating-speed rating is implied.
Direct-connected compound-engine questions
Why does the generator rotate at the engine speed?
Its rotor is directly connected to the crankshaft. This model includes no intervening gear or belt ratio.
Is 90° the only valid crank phase?
No. It is a common illustrative choice, but the appropriate phase depends on the engine and its operating requirements. Changing it here shows the relative piston motion.
Are the volume outputs steam consumption?
No. They are geometric full-bore displacement per piston stroke, before clearance, rod area or valve timing is considered.
What happens if the LP bore is smaller?
The geometry and volumes still display, with a note that the chosen dimensions reverse the usual larger-LP arrangement.
Can this calculate generator power?
No. Dimensions and rpm alone do not determine indicated steam power, mechanical losses or electrical output.
Historical construction reference
Hiscox, Mechanical Movements, Powers, Devices and Appliances, printed page 192, figure 718, shows a vertical compound engine directly connected to a multipolar dynamo. The cutaway uses adjustable dimensions and illustrative internal proportions to explain the shaft and piston motion.
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