Stoking the steam, one engine at a time…
Steam boat
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CygnetReal world steam power

Type: Single cylinder,Vertical, Inverted Y Trunk standard, slide valve, double acting.
Bore: 2 1/4 in
Stroke: 2 in
Height: 13 in
Availability: 1976-98.
Design: Trunk Standard

Stacks Image 80


2 1/4 in. bore 2 in stroke.

Design speed Up to 1,000 r.p.m.
Steam pressure Up to 100 p.s.i.
Maximum power 1 1/2 h.p at 800 r.p.m.

Condensing type: 41 lb. (18.5 Kg)
Non Condensing type: 52 lb. (23.5 Kg)

Condensing type: L 15 in x H 13 5/16 in x W 10 3/4 in.
Non Condensing type: 8 1/2 in x H 13 5/16 in x W 6 3/4 in.

Pipe connections:
Steam: 1/2 in dia tapped 26 t.p.i.
Exhaust: 5/8 in tapped 26 t.p.i.

We know many Model Engineers own boats, so we are now offering these famous steam engines in "kit" form.
This is a single cylinder, double acting, single expansion engine fitted with slide valves and Stephenson's link reverse gear.

List of Castings and Parts

CAST IRON.- Cylinder with steam chest and steam ports cast in, 1 each top and bottom covers, 2 Piston Bodies, 1 Piston Ring, 1 Valve Chest Cover, 2 Standards, 1 Bed Plate, 1 Box Bed, 1 Eccentric Sheave, 1 Slide Valve, 1 disc wheel, 1 Stop Collar, 2 Crank Balance Weights.
STEEL.- 1 Connecting Rod, 1 Eccentric Rod, 1 Crank Shaft, 12 Bearing Caps.
1 each Piston and Valve Gland, 1 pair Eccentric Strap, 2 pairs Main Bearing Brasses, 1 Valve Stuffing Box, 1 Valve Rod Guide, 1 Slide Valve Nut, 1 each Steam and Exhaust Flanges, 2 Connecting Rod Brasses.
STEEL BAR, etc,-1 Piston Rod and Crosshead, 1 Valve Rod, 1 piece Steel for Valve Rod Head and Crosshead Bolt, Sheet Steel for Lagging.
DRAWING.- 1 Large sheet with all details, full size.

Weight packed. 35-lbs.


EXTRAS.- All Studs, Nuts, Bolts and Screws, 12/-; Drain Cocks, 6/- per pair; Cylinder Lubricator, 4/6; Reversing Gears with castings in Steel and Gunmetal and all bolts, Studs, and Nuts with drawing, 12/6; 1 set Pump Castings, with all materials and drawing, 5/-.-
For steam canoes this is an ideal engine, and if fitted with slip eccentric reversing gear will be found economical and very efficient.

Originally available as a set of castings the engine was later released as a kit of machined parts for easy construction.
The No 5a used to create this single cylinder engine is the later type with the seperate valve chest. The boxed has been replaced by a slim base casting used to mount the engine and all the new ancillary equipment. This includes just about everything required to set up an engine working in a real world situation with a boiler. The boiler feed pump allows water to be pumped into the pressurised boiler to replace that lost in the form of steam. The water output is tied to the engine speed, the pump is usually more powerful than required to replace the water and a bypass valve is installed to allow the pump to feed back into the water reservoir when the boiler doesn't require more water. Oil feed pump automatically keep the important parts of the engine lubricated from a large reservoir. Vacuum air pump are also included but require a steam condenser to work. A condenser uses exhaust steam to preheat the water used to feed into the boiler saving energy, it also condenses the steam back into water which also feeds back into the water container. This is important as salty water cannot be used in a boiler, only clean fresh water. Connected directly to the exhaust, a condensor drops the pressure as the steam is condensed. By connecting a vacuum pump a constant vacuum can be maintained, this increases the pressure differential between exhaust and steam pressures. The engine is available in condensing or non condensing versions. A single cylinder version was also available called the Cygnet. The engine, creating 1 1/2 Hp was easily capable of driving a small boat.

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Swan with water pump and condenser fitted.

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Swan castings the Cygnet obviously only has castings for a single No.5a engine.

Cant find a Cygnet running so here is a Swan running.

Image 6

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