Sentinel boiler
Encyclopedia
The Sentinel boiler was a design of vertical boiler
, fitted to the numerous steam waggon
s built by the Sentinel Waggon Works
.
The boiler was carefully designed for use in a steam wagon: it was compact, easy to handle whilst driving, and its maintenance features recognised the problems of poor feedwater
quality and the need for it to be maintained by a small operator, rather than a major locomotive works.
Although this design was used in most of Sentinel's products, they also produced larger boilers of quite different types for their railway locomotives.
, so as to reduce the effects of tilting due to hill climbing or uneven roads disturbing the water level. It also provides a compact boiler that leaves adequate space in the cab for the crew, controls and coal bunker, whilst leaving as much as possible of the wagon's overall length available for the useful load.
The boiler is a watertube boiler, with these tubes contained within a vertical, cylindrical outer drum. This drum is double-walled and forms a water jacket around the boiler, with a large vertical flue within. The inner flue has a complex cross section. It is stepped in three diameters, tapering towards the top. The central region is square in section, rather than round.
The main heating surface is provided by water-tubes in this squared section. These tubes are short, straight and pass between the flat faces of the squared section in a grid pattern. There are eight layers of tubes, four banks of six each way.
A space is left in the centre of the water-tube banks for the firing chute. The firebox is top-fired (and lit) through this chute and there is no side firedoor. The lower part of the water-jacketed barrel surrounds the firebox. The narrow waterspace here encourages rapid steam raising. Firing is simple, with a thick fire relative to its area and fuel simply poured down. Beneath the grate is a water-filled ashpan, to prevent hot embers falling onto the road. Draught is controlled by a damper in the side of the ashpan, between the grate and the water tray.
Above the tube nest the water space widens to form an increased reservoir, protecting against tilting. Sentinel's drawings permitted a hill climb gradient of 1 in 6. Modern regulations for buses require a safe tilt of 35°. The narrowed flue in this area is used, where fitted, to house the superheater
.
An unusual feature of the Sentinel boiler was the "exhaust drying box", a small reheater, in the upper part of the boiler flue, immediately before the blastpipe nozzle. This heated the exhaust steam to avoid it condensing into a visible white plume. It was a requirement of the Highways and Locomotives Act 1878 that engines should "consume their own smoke".
that was either dirty or contaminated with dissolved minerals. Untreated, this builds up boiler scale on the tubes and particularly deposits sludge in the lower parts of the boiler. Both of these disturb circulation and risk local overheating and damage, scale also reduces boiler efficiency and wastes fuel.
The Sentinel boiler was designed to cope with these problems, and to permit easy cleaning of the waterspace. As well as the usual blow-down cock for daily use, the entire boiler could be dismantled easily. The outer shell was in two sections, inner and outer drum, and were joined by a bolted ring joint at top and bottom. Regular servicing (depending on water conditions) was to separate the water-tubes in their drum from the boiler outer shell, so that they could be cleaned. Sludge dropped free on opening the shell and the short, straight tubes could easily be cleaned with brush or scraper.
Several other vertical boilers, such as the Straker
, had similar arrangements for lifting their shells off the tube nest. The Sentinel though left the outer shell in place and instead dropped the tube nest downwards (having first removed the ashpan). This had the advantages that it required simpler lifting gear: the waggon would be raised on ramps or over a pit, the bolts removed and then the tube bank lowered with a block and tackle
from a fixed beam, without requiring a mobile crane that could lift it and then move it sideways. Secondly the many pipe connections to the outer shell were left undisturbed, making the operation quicker.
Dropping the firebox was not required at every washout and was recommended at intervals of 2 to 12 months, depending on water quality.
. Manufacture of these was sub-contracted to the well-known boilermakers Galloway
of Manchester. When Galloway closed in 1932, Sentinel switched back to their square pattern.
s, buses
and other vehicles.
Mann's of Leeds
used a derivation of the Sentinel boiler in their "Express" wagon, launched in 1924.
models.
Their larger locomotives used a range of boiler designs, but all with water-tubes.
Vertical boiler
A vertical boiler is a type of fire-tube or water-tube boiler where the boiler barrel is oriented vertically instead of the more common horizontal orientation...
, fitted to the numerous steam waggon
Steam wagon
A steam wagon is a steam-powered road vehicle for carrying freight. It was the earliest form of lorry and came in two basic forms: overtype and undertype – the distinction being the position of the engine relative to the boiler...
s built by the Sentinel Waggon Works
Sentinel Waggon Works
Sentinel Waggon Works Ltd was a British company based in Shrewsbury, Shropshire that made steam-powered lorries, railway locomotives, and later, diesel engined lorries and locomotives.-Alley & MacLellan, Sentinel Works, Jessie Street Glasgow:...
.
The boiler was carefully designed for use in a steam wagon: it was compact, easy to handle whilst driving, and its maintenance features recognised the problems of poor feedwater
Boiler feedwater
Boiler feedwater is water used to supply a boiler to generate steam or hot water. At thermal power stations the feedwater is usually stored, pre-heated and conditioned in a feedwater tank and forwarded into the boiler by a boiler feedwater pump....
quality and the need for it to be maintained by a small operator, rather than a major locomotive works.
Although this design was used in most of Sentinel's products, they also produced larger boilers of quite different types for their railway locomotives.
Description
Sentinel boilers are vertical, as was common for many designs of steam wagonSteam wagon
A steam wagon is a steam-powered road vehicle for carrying freight. It was the earliest form of lorry and came in two basic forms: overtype and undertype – the distinction being the position of the engine relative to the boiler...
, so as to reduce the effects of tilting due to hill climbing or uneven roads disturbing the water level. It also provides a compact boiler that leaves adequate space in the cab for the crew, controls and coal bunker, whilst leaving as much as possible of the wagon's overall length available for the useful load.
The boiler is a watertube boiler, with these tubes contained within a vertical, cylindrical outer drum. This drum is double-walled and forms a water jacket around the boiler, with a large vertical flue within. The inner flue has a complex cross section. It is stepped in three diameters, tapering towards the top. The central region is square in section, rather than round.
The main heating surface is provided by water-tubes in this squared section. These tubes are short, straight and pass between the flat faces of the squared section in a grid pattern. There are eight layers of tubes, four banks of six each way.
A space is left in the centre of the water-tube banks for the firing chute. The firebox is top-fired (and lit) through this chute and there is no side firedoor. The lower part of the water-jacketed barrel surrounds the firebox. The narrow waterspace here encourages rapid steam raising. Firing is simple, with a thick fire relative to its area and fuel simply poured down. Beneath the grate is a water-filled ashpan, to prevent hot embers falling onto the road. Draught is controlled by a damper in the side of the ashpan, between the grate and the water tray.
Above the tube nest the water space widens to form an increased reservoir, protecting against tilting. Sentinel's drawings permitted a hill climb gradient of 1 in 6. Modern regulations for buses require a safe tilt of 35°. The narrowed flue in this area is used, where fitted, to house the superheater
Superheater
A superheater is a device used to convert saturated steam or wet steam into dry steam used for power generation or processes. There are three types of superheaters namely: radiant, convection, and separately fired...
.
An unusual feature of the Sentinel boiler was the "exhaust drying box", a small reheater, in the upper part of the boiler flue, immediately before the blastpipe nozzle. This heated the exhaust steam to avoid it condensing into a visible white plume. It was a requirement of the Highways and Locomotives Act 1878 that engines should "consume their own smoke".
Washout
By the nature of their use, steam wagons were often required to use feedwaterBoiler feedwater
Boiler feedwater is water used to supply a boiler to generate steam or hot water. At thermal power stations the feedwater is usually stored, pre-heated and conditioned in a feedwater tank and forwarded into the boiler by a boiler feedwater pump....
that was either dirty or contaminated with dissolved minerals. Untreated, this builds up boiler scale on the tubes and particularly deposits sludge in the lower parts of the boiler. Both of these disturb circulation and risk local overheating and damage, scale also reduces boiler efficiency and wastes fuel.
The Sentinel boiler was designed to cope with these problems, and to permit easy cleaning of the waterspace. As well as the usual blow-down cock for daily use, the entire boiler could be dismantled easily. The outer shell was in two sections, inner and outer drum, and were joined by a bolted ring joint at top and bottom. Regular servicing (depending on water conditions) was to separate the water-tubes in their drum from the boiler outer shell, so that they could be cleaned. Sludge dropped free on opening the shell and the short, straight tubes could easily be cleaned with brush or scraper.
Several other vertical boilers, such as the Straker
Straker-Squire
Straker-Squire was a British automobile manufacturer based in Bristol, and later Edmonton in North London....
, had similar arrangements for lifting their shells off the tube nest. The Sentinel though left the outer shell in place and instead dropped the tube nest downwards (having first removed the ashpan). This had the advantages that it required simpler lifting gear: the waggon would be raised on ramps or over a pit, the bolts removed and then the tube bank lowered with a block and tackle
Block and tackle
A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.The pulleys are assembled together to form blocks so that one is fixed and one moves with the load...
from a fixed beam, without requiring a mobile crane that could lift it and then move it sideways. Secondly the many pipe connections to the outer shell were left undisturbed, making the operation quicker.
Dropping the firebox was not required at every washout and was recommended at intervals of 2 to 12 months, depending on water quality.
Firebox shape
Sentinel's best-known flue design was the square-section, but at one time they also used a circular corrugated design, with the water-tubes arranged in a spiralHelix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
. Manufacture of these was sub-contracted to the well-known boilermakers Galloway
W & J Galloway & Sons
W & J Galloway and Sons was a British manufacturer of steam engines and boilers, based in Manchester, England. The firm was established in 1835 as a partnership of two brothers, William and John Galloway. The partnership expanded to encompass their sons and in 1889 it was restructured as a limited...
of Manchester. When Galloway closed in 1932, Sentinel switched back to their square pattern.
Steam waggons
The boiler was used throughout Sentinel's range of steam waggons, from the earliest to the last. It was also used for their steam tractorSteam tractor
A steam tractor is a vehicle powered by a steam engine which is used for pulling.In North America, the term steam tractor usually refers to a type of agricultural tractor powered by a steam engine, used extensively in the late 19th and early 20th centuries.In Great Britain, the term steam tractor...
s, buses
Steam bus
A steam bus is a bus powered by a steam engine. Early steam-powered vehicles designed for carrying passengers were more usually known as steam carriages, although this term was sometimes used to describe other early experimental vehicles too.-History:...
and other vehicles.
Mann's of Leeds
Mann's Patent Steam Cart and Wagon Company
Mann’s Patent Steam Cart and Wagon Company manufactured steam powered road vehicles in Leeds, England.- Early history :The company was founded by James Hutchinson Mann, a native of Leeds. Mann had been apprenticed to J&H McLaren & Co. and also worked for Marshall, Sons & Co. of Gainsborough...
used a derivation of the Sentinel boiler in their "Express" wagon, launched in 1924.
Railway locomotives
This particular boiler design was not widely used for Sentinel's railway locomotives. Narrow-gauge locomotives used it, as did the smaller standard gaugeStandard gauge
The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...
models.
- LNER Class Y1LNER Class Y1The LNER Class Y1 was a class of 0-4-0 geared steam locomotives built by Sentinel Waggon Works for the London and North Eastern Railway and introduced in 1925...
- LNER railmotors
Their larger locomotives used a range of boiler designs, but all with water-tubes.
Comparable boiler designs
- Straker boiler
- a direct precursor of the Sentinel
- Robertson boiler
- a comparable fire-tube design
Other boiler designs used by Sentinel
- Sentinel-Doble boiler
- Sentinel recruited the American steam carSteam carA steam car is a light car powered by a steam engine.Steam locomotives, steam engines capable of propelling themselves along either road or rails, developed around one hundred years earlier than internal combustion engine cars although their weight restricted them to agricultural and heavy haulage...
developer Abner DobleAbner DobleAbner Doble , was an American mechanical engineer who built and sold steam-powered automobiles. His father was William Ashton Doble, inventor of the Doble water wheel, and his grandfather and namesake was the founder of the Abner Doble Company.Abner Doble began apprenticing at his family's factory...
to develop an advanced monotube boiler for them.
- Woolnough boiler
- a three-drum water-tube boilerThree-drum boilersThree-drum boilers are a class of water-tube boiler used to generate steam, typically to power ships. They are compact and of high evaporative power, factors that encourage this use...
used for their larger locomotives.http://www.aqpl43.dsl.pipex.com/museum/locoloco/colombia/colombia.htmhttp://www.steamindex.com/manlocos/sentinel.htm
- locomotive boiler
- used on the handful of overtype steam waggons built by Sentinel.