Sunday, 21 August 2011

200HP Pre-war Sentinel Locos (1)

Sentinel 7109 is a 200 HP type; however, Sentinel also produced various other 200 HP types before they settled on the 7109 configuration. One such type proposed was the double centre-engined type shown below. However (see comments below the posting), this type was never apparently built although others were (but I don't have diagrams for them!).
Double Centre-engined 200 HP Locomotive
The front engine was intended to be linked to the front axle and the rear engine to the rear. Those specified to be low geared (and hence high torque) also had their engines locked together to prevent wheel-spin on one axle.

Compare this to Sentinel 7109 with its engines at the front (and check the comments below).

Sentinel 7109 - A balanced double-engined 200 HP locomotive
Both the types and others could be built with double gearing; however, 7109 is only single geared.


  1. John Hutchings of the Industrial Locomotive Society ( kindly prompted me that whilst Sentinel started out with basic designs such as in the diagrams, what was actually delivered was often quite different in appearance.

    In those days, mass production was not common and so it was fairly straight forward to cater for individual customers' requirements. Sentinel delivered locomotives all over the world and adaptations were made to suit the various climates (e.g. open cabs for hot countries, closed cabs for cold). More dramatically, where track was not of sufficiently heavy duty, additional axles could be included in the design to spread the load.

    So please regard the diagrams as more of a basic idea than the final product!

  2. John Hutchings of the Industrial Locomotive Society ( is keeping me on track. I now realise I've misinterpreted my source "Sentinel" Patent Locomotives and incorrectly concluded that the upper diagram on this posting depicted the locos delivered to Spain and India. Text in the posting is now altered accordingly! Clearly this is a more interesting subject than I'd thought!

    John's comment:
    "The reason I am so cautious in ascribing outline diagrams to specific locomotives is that people who read the internet tend to take these things as gospel. The upper outline drawing on your blog may (or may not) refer to Job 7071 that was intended as a 200HP loco. The engines were mounted together but not intended to be physically connected unless, as the diagram says, conditions required it. We do not know for certain what happened next but the loco drawing office probably made the next logical step of mounting both engines on a common gear case, this coming to fruition as your 7109. 7071 was not in the end built, although some material was certainly ordered for it.

    The locomotives for Spain and India bore no relation to the (possible) 7071 outline. The Indian locomotive 7024 was more akin to the CEDG types with one engine mounted amidships (same as 6515 at Quainton) and the other engine at the outer end of the frames behind the water tank. The centre engine drove the front axle and the rear one the rear axle, with no coupling between axles. The boiler was of the “twin” pattern, essentially this was two boilers as in 6515 mounted side-by-side and connected by two external pipes.

    The 6-wheeled examples for Spain were much the same in layout, one engine in the middle and one behind it, but not right at the back. The two side water tanks were mounted behind the cab with the second engine mounted between, accessed via a door at the rear of the loco. Drive from the centre engine was to the middle axle and from the other engine to the rear axle. The boiler was similar to the one in 7109, but yours was to drawing 9225 (as was the replacement supplied by Abbott’s) whereas pattern 10460 was fitted in the locomotives for Spain."

    I realise photos would be very useful to illustrate John's comments. I'll check the copyright situation to see what's feasible.


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