A Cochran boiler is a vertical, multitubular, fire-tube boiler: a cylindrical shell with a domed crown, a hemispherical firebox at the bottom, a brick-lined combustion chamber outside the shell and horizontal smoke tubes running back through the water to a smoke box and chimney. That is the machine the name usually means. The boiler we surveyed with a thermal camera is a modern Cochran package boiler, which is a different arrangement, and it is the one every number here belongs to.
The shell stands upright with a domed crown. The firebox is hemispherical and sits at the bottom, surrounded by water on every side, and is fired through a door onto the grate. Gas leaves it through a short flue pipe into a combustion chamber that stands outside the shell and is lined with firebrick. From there the gas turns into horizontal smoke tubes that run back through the water to a smoke box at the front, and out up the chimney.
We have not surveyed a vertical Cochran, so no dimensions and no temperatures are given for it. Everything with a number on this page is from the package boiler we did survey.
| Part | What it does |
|---|---|
| Hemispherical crown | The domed top of the shell. The dome carries pressure without staying. |
| Steam space | Above the water line, where steam collects before the stop valve. |
| Water space | Surrounds the firebox and the tubes on all sides. |
| Firebox | Hemispherical, fired through the fire door onto the grate. |
| Grate and ash pit | The fuel bed, and what falls through it. |
| Flue pipe | A short duct taking gas from the firebox into the combustion chamber. |
| Combustion chamber | Brick lined, sitting outside the shell, where the gas finishes burning. |
| Smoke tubes | Horizontal, running through the water from the combustion chamber to the front. |
| Smoke box | Collects the gas leaving the tubes. |
| Chimney | Takes the gas out of the building. |
| Mountings | Safety valve, stop valve, pressure gauge, water gauge glass, manhole, blow-off cock, fusible plug. |
Water surrounds the firebox and every tube. Steam collects above the water line and leaves through the stop valve on the crown. That arrangement is what the name describes: a vertical shell, many tubes, gas inside them.
The Cochran we surveyed is a horizontal package shell boiler, not the vertical machine above. Same manufacturer, different arrangement: the furnace tube runs along the shell, the gas turns at the rear and comes forward through two more passes, and an economiser stands in the flue behind it.
Six surfaces were read with a thermal camera and rebuilt in CAD. The readings are of the outside of each item on a boiler under load.
| Surface | Bare | Area | Heat loss |
|---|---|---|---|
| Front, burner door | 120 °C | 5.32 m² | 7,973 W |
| Rear end plate | 130 °C | 5.32 m² | 9,063 W |
| Economiser casing | 126 °C | 11.31 m² | 18,327 W |
| Rear valves and steam set | 180 °C | 2.75 m² | 7,095 W |
| Feed and condensate side | 100 °C | 4.22 m² | 4,713 W |
| Manhole and hatches | 180 °C | 0.39 m² | 1,126 W |
| Six surfaces, together | — | 29.31 m² | 48,297 W |
Bare 49.75 kW across 28 components. Under removable modules the same components shed 2.58 kW. Areas carry a geometry allowance for bolts and irregular surface; heat loss is calculated to ISO 12241 from the measured surface temperature.
| Vertical Cochran | The package boiler we surveyed | |
|---|---|---|
| Shell | Vertical, domed crown | Horizontal, flat end plates |
| Furnace | Hemispherical firebox at the bottom | Furnace tube along the shell |
| Combustion chamber | Outside the shell, brick lined | Inside, at the rear |
| Passes | Firebox, chamber, tubes | Three |
| Where heat escapes | Crown, firebox plate, smoke box | End plate, front door, economiser casing, valves |
| Measured by us | No | Yes, six surfaces |
A Cochran boiler is a vertical, multitubular, fire-tube boiler: a cylindrical shell with a domed crown, a hemispherical firebox, an external brick-lined combustion chamber and horizontal smoke tubes running to a smoke box and chimney.
Fire tube. The gas travels inside the tubes and the water sits around them in the shell.
Grate and firebox, then the flue pipe, then the combustion chamber outside the shell, then the horizontal smoke tubes, then the smoke box, then the chimney.
It sits outside the water space, so the lining keeps flame off the plate behind it.
Safety valve, main stop valve, pressure gauge, water gauge glass, manhole, blow-off cock and fusible plug.
No. We surveyed a modern Cochran horizontal package boiler. The measured figures on this page — 49.75 kW bare across 28 components — belong to that machine, not to the vertical one in the first diagram.
The economiser casing at 126 °C over 11.31 m², which is 18,327 W, then the rear end plate at 130 °C, which is 9,063 W.
The surveyed view this page came from, with every element on it.Open
→/ 02The rear plate and the economiser behind it: 126 to 130 °C, the largest single loss on the machine.Open
→/ 03What each mounting is, which are required, and what the set sheds at 180 °C.Open
→| Survey | FLIR S62 Pro, emissivity 0.90, reflected 25 °C, 3 m, full radiometric correction. UK commercial boiler house. |
| Geometry | Rebuilt in CAD from the surveyed machine. Area allowances are stated on the page they are used on and are allowances, not measured areas. |
| Calculation | ISO 12241 steady state. Heat loss is calculated from the measured surface temperature and the modelled area — it is not metered. Full method, basis and limits. |
Where surface loss sits inside the indirect method, and what 49.8 kW is against the fuel input.Open
→/ 02What has to be opened, how often, and who signs it off under PSSR 2000.Open
→/ 03Which machine this is, and why the losing surfaces differ between the two.Open
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