It was actually a high pressure water tube boiler that would raise steam very quickly so the fire could be dropped if it was idle for long periods. Sentinel Waggon Works (note the spelling) already had a successful range of steam road trucks and applied the same technology to railways, making a popular range of economical light shunters and steam railcars.
The LMS, LNER and even the GWR all had a few shunters, and the LNER bought their railcars.
They also sold a few full size steam motor locomotives overseas, using three drum water tube boilers.
The steam motor and chain drive made it easy to rebuild the shunters with Rolls Royce diesel engines, and the company was eventually owned by Rolls Royce.
There were two of these at Bristol (4)7190/7192 ) for working the very short radius yard at Avon Street. There were also L&Y Pugs 51212 &
51202 at that time.
The yard was on the quays of Bristol City Docks and provided the liason between the Ships and the Midland Railway by using barges. There was a hydraulic lift for barges but I cannot find much detail of that.
The approach line to the yard is the only surviving piece of the Barrow Road/ St.Phillips complex and is employed for the Trash Transfer trains.
And one of the first of to introduce lager to the UK Market. It surprises some who consider the devil arrived with it in the 1960's and 1970's to find that Allsops bought a lager Plant in 1897. Ind Coope then went on to develop lager further after the merger. and also acquired the Wrexam lager company which was also established in the 1890's. To get back to railway matters there is a photo which appears occasionally which shows the lager Tanks for one of those lager breweries being carried on a train. And ISTR that in some photos of a Bullied Tavern car there is a cask on the counter which if you look closely has Allsops stamped on the end.
We have one on our exhibition layout Boxer's Yard , working as the shunter on the private sidings. It's a Nu-Cast kit, running on a Spud motor bogie. Lovely little engine and very reliable, often running for the whole of both days of a show. IIRC, it was the first white metal loco kit my Dad ever built.