The Dion vehicle boiler in Hiscox figure 183 has a central water-and-steam drum inside an annular outer drum. Short inclined water tubes connect them across the surrounding gas space. This is a different arrangement from vertical tubes between an upper drum and a lower mud ring. The cutaway and plan view below make the central drum, surrounding ring and radial tube connections visible.
Dion Vehicle Boiler Interactive Calculator
Inspect the central drum, annular outer drum and inclined radial tubes. Compare grate area using your steam demand and two measured grate-area evaporation rates.
Equation Used
- Rate inputs refer to steam flow per unit of grate area.
- Rates and demand describe comparable operating conditions.
- Equivalent diameter is an equal-area circular footprint, not shell diameter.
- Historical boiler drawing is schematic and not scaled from calculated grate area.
Enter evaporation rates measured per grate area under comparable conditions. Defaults are examples, not historical performance data.
A central drum inside a surrounding ring
The front section cuts through the central drum and the annular outer drum. The two blue columns at the sides are opposite sections of the same surrounding ring. Short tubes rise inward from that ring to the central drum. The plan view below shows how those tubes extend radially around the center.
The grate and fire are below. Gas rises through the spaces around the water-filled tubes, then passes into the hood and chimney. Water stays inside the drums and tubes; steam collects in the upper central space and leaves through a separate outlet. Gas markers are hidden where the solid cutaway tube walls pass in front of them.
The geometry follows Hiscox’s historical section. Tube count, wall thickness, fittings and proportions are explanatory rather than fabrication dimensions. The animation shows gas movement and steam release, not a solved circulation rate or a pressure transient.
What the calculator compares
Hiscox identifies the design as a light, quick-firing boiler for a motor carriage. The central drum and surrounding annular drum form a compact arrangement. Actual pressure, steam output and vehicle installation details require records for the particular boiler.
The calculator compares required grate area for a stated steam demand using two measured evaporation rates per unit of grate area. These rates must refer to comparable fuel, draught, feedwater and steam conditions. The defaults are arithmetic examples, not documented Dion performance values.
The area calculation alone does not size the pressure shell, heating surface, tube banks, chimney or combustion volume. The animation’s boiler outline therefore remains a schematic while its separate grate-footprint comparison responds to the area result.
Area from steam demand and measured evaporation
Let m be required steam delivery in kg/h and E be measured steam delivery per square metre of grate in kg/(h·m²). The comparison area is A=m/E in m².
The calculator sorts the two entered rates. The larger rate gives the smaller area; the lower rate gives the larger area. The midpoint result uses the arithmetic midpoint of the two rates, then divides demand by that midpoint. It is not the average of the two area results.
For the midpoint area, an equivalent circular grate has diameter d=2√(A/π). This is an area conversion, not a complete boiler design. Grate area and heat-transfer surface area are different quantities and must not share an evaporation-rate basis accidentally.
Grate-area comparison does not determine allowable pressure or safety-valve settings. Those require the boiler’s design and certified equipment data.
Example using explicitly supplied rates
With a steam demand of 100 kg/h and supplied grate-area evaporation rates of 70 and 90 kg/(h·m²), the comparison areas are 100/90=1.111 m² and 100/70=1.429 m².
The midpoint rate is 80 kg/(h·m²), so its area is 1.250 m². An equal-area circle has diameter 1.262 m. This is an illustrative input set; it is not a claim that the historical boiler had that grate or delivered that steam flow.
Doubling the demand with unchanged measured rates doubles all three areas and increases equivalent diameter by √2. Exchanging the two rates leaves the results unchanged.
Grate area and actual boiler performance
The short inclined tubes and concentric drums distinguish this design. The plan inset explains why a longitudinal section shows two side columns rather than two unrelated headers. The number of illustrated radial tubes is reduced for readability.
The calculation assumes the entered measured rate can be used for the comparison being made. It does not derive that rate from fuel, pressure or tube geometry. It does not predict warm-up time, safe pressure, tube life, natural-circulation stability or fuel conversion suitability.
The fixed waterline and animated markers explain the arrangement. Use the actual boiler’s documentation for water levels, tube dimensions, operating limits and maintenance requirements.
Dion boiler questions
Are the side water columns separate tanks?
No. In this section they are the two cut sides of one annular drum surrounding the central drum.
Are these vertical tubes?
No. The source shows short inclined connections between the surrounding drum and the central drum. The plan view shows their radial arrangement.
Does the gas travel inside the blue tubes?
No. Water occupies the tubes; gas passes around their outside surfaces.
Why do the two rate inputs sort themselves?
Either measurement may be larger. The higher measured rate gives the smaller area, so the calculator sorts the results while keeping both entered rates.
Can I use heating-surface evaporation data?
Only after changing the area basis consistently. This calculator specifically uses evaporation per unit of grate area, not per unit of tube heating surface.
Does this calculate safety-valve settings?
No. The calculator compares grate areas from steam demand and measured evaporation rates. It does not determine allowable boiler pressure or safety-valve settings.
Construction reference
Gardner D. Hiscox, Mechanical Movements, Powers and Devices, printed page 59, figure 183: central water-and-steam drum, surrounding annular drum and short inclined connecting tubes. The grate-area equations are dimensional arithmetic applied to user-supplied measurements, not a performance rating from that source.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
