Steam engines
as of 0.6.8
An engine takes steam from the pipe on its inlet face and drives exactly one sub-machine seated in its drive cell. It makes no power of its own account: the sub-machine decides what the power does, and an engine with no sub-machine attached draws no steam at all.
The two engines
| fact | Watt | Cornish low | Cornish normal | Cornish high |
|---|---|---|---|---|
| engages at | 2 atm | 5 atm | 6 atm | 7 atm |
| wears above | 4 atm | 8 atm | 8 atm | 8 atm |
| steam drawn | 30 L/s | 8 L/s | 16 L/s | 32 L/s |
| power delivered | 0.3 | 0.2 | 0.4 | 0.8 |
| shaft load it holds | 0.6 | 0.4 | 0.8 | 1.6 |
| condensate out | 1 L/s | 0.3 L/s | 0.6 L/s | 1.2 L/s |
The Watt Engine runs on a lot of low-pressure steam and is built from iron or steel. The Cornish Engine is steel and meters its steam with control rods, so it wrings more work out of less: on normal it does more than a Watt on half the steam.
The engine draws its full steam rate whenever it is engaged, and the power it delivers scales with the share of that steam the line can actually supply. A starved line does not stop an engine, it makes it weak.
An engine also sets the output pressure of its sub-machine, at 75 per cent of its own inlet steam pressure. That is what a pump lifts against and what a blower blows at.
Matching an engine to a boiler
A Cornish Boiler chokes at 5 atm. That is above the Watt Engine's 4 atm wear point, so a Watt behind a Cornish boiler needs a Piping (Pressure Valve) gated around 2.5 to 3 atm, hung off the run the engine sits on and venting to air or to an overflow, or it will break. It is also only just at the Cornish Engine's low setting and below its normal and high settings, so a Cornish engine wants a Lancashire Boiler, which chokes at 12 atm.
A Lancashire needs a valve of its own, for the same reason. Every Cornish setting wears above 8 atm and steel pipe bursts at 10 atm, both well under the boiler's 12 atm choke, so an ungated Lancashire line breaks a Cornish engine in 60 s exactly as an ungated Cornish boiler breaks a Watt. Hang a pressure valve off the engine's run there too, gated at 8 atm or under.
A relief valve only holds a line the engine is drawing from. An engine with no sub-machine, or one whose pump has lost its intake, draws no steam while its over-pressure timer keeps running, and a valve venting 8 L/s cannot hold a run down against a Cornish boiler's 32 L/s on its own: the line climbs to the boiler's choke pressure and the engine bursts 60 s later. Shut the steam line or let the fire die before leaving an engine standing without a sub-machine.
Steam supply is the other half of the match. A Cornish boiler makes 32 L/s, which is one Watt with nothing to spare, or two Cornish engines on normal. A Lancashire makes 48 L/s, which is three Cornish engines on normal, or one on high with a second on normal beside it.
Throttle, breaking and repair
The Cornish engine's control rods answer a wrench on the engine's own cell and on the cell directly above it: right-click raises the setting, ctrl and right-click lowers it. The look-at line names the setting and the band it runs in.
Above the wear pressure an engine runs hot for 60 s and then bursts. It is inert until repaired, and dropping back into the band before the 60 s are up clears the count. Right-click a broken engine with a wrench in hand to read the bill, then right-click again with the materials in your hotbar. A Watt Engine takes 4 iron or steel plates and 2 iron or steel rods; a Cornish Engine takes 4 steel plates and 2 steel rods.
Spent steam leaves as hot condensate on the engine's water outlet face, 1 L/s from a Watt Engine. A water line there takes it, at no pressure of its own; an unplumbed face sprays it on the ground.
Why they feel weak, and what they are for
There is no kilowatt or horsepower figure anywhere in this mod, and the power numbers above are bare ratios. What they buy is shaft load: an engine's Mechanical Power Generator holds a load of twice the engine's power at full speed, so 0.6 for a Watt Engine and 1.6 for a Cornish Engine on high. A vanilla helve hammer resists 0.125, which puts a Watt at about five hammers and a Cornish on high at about thirteen. The game's own handbook still says two and six; those figures predate the 0.6.6 rebalance, which raised the load an engine holds per unit of power so that an engine out-pulls a vanilla waterwheel rather than giving up where the wheel merely bogs down.
Pulling power is not the reason to build steam, though. What it is instead:
- Power where there is no river, underground or in a walled shop.
- Power on demand, which starts and stops with the fire rather than the season.
- The only drive for the air blowers of Steelmaking Expanded, which is what the blast furnace and the Bessemer converter need and what no waterwheel provides.
One engine drives one sub-machine. A plant that needs a blower and a pump needs two engines, and usually two boilers, because the steam adds up.