GWR 3100 Class

The Great Western Railway (GWR) 3100 Class is a class of 2-6-2T side tank steam locomotive. This was developed from one of GJ Churchward's pioneer designs; the experimental No 99. The basic design was so sound that derivatives were built until the end of the company's life in 1948 and even beyond.

The development was gradual but a little convoluted, summarised as follows:-

No 99 was produced in 1903 and given an extended trial over the next two years. Fitted with the standard number 2 boiler running at 200 p.s.i., flat topped tanks and driving wheels of 5 feet 8 inches diameter, this was the genesis of 289 similar locos that were to follow. Thirty nine more examples were built to this initial design. This production batch differed from the prototype only in that the tank tops were sloping to aid visibility and the cab sides were incorporated into the tanks. The running numbers of this batch were 3111 to 3149 and the prototype was logically renumbered 3100.

1906 saw the first alteration to the design of the class, when numbers 3150 to 3190 (known as the GWR 3150 Class) were produced using the larger standard number 4 boiler, again running at 200 p.s.i. These two classes were the basis of what was to follow for over forty years.

A renumbering in 1927 saw the original forty were renumbered 5100 and 5111 to 5149, the next additions to the class filled in the numbers 5101 to 5110 and extended the class to 5189. These locos were known as the GWR 5101 Class but were really little changed from the first batch but had an increased axle loading of 17 tons 12 hundredweight. Bunkers were of the standard Collett design with greater coal capacity.

1931 saw the next batch of engines, the initially sixty strong GWR 6100 Class, had a useful alteration to the original design in the use of 225 p.s.i. boiler pressure. This increased the tractive effort from 24,300 pounds to 27,340 pounds.

Additions to the 51xx class were made until available numbers were exhausted, and forty engines were then built in the 41xx series.

In 1938 Collett rebuilt some of the oldest locos in the 31xx series with a view to using them as bankers, particularly from Severn Tunnel Junction shed. One of the two classes of rebuilds were a "new" 3100 class derived from the old 3150 class. These engines used the standard class 4 boiler again, but pressed to 225 p.s.i. and using smaller coupled wheels of 5 feet 3 inches diameter, and a half inch increase in cylinder diameter, nominal tractive effort rose to 31,170 pounds. Almost impossible to pick was a 2" reduction in pony truck wheel diameter to 3'. Only five engines were ever modified, namely 3173, 3156, 3181, 3155 and 3179 which were rebuilt as 3100 to 3104 respectively.

The other modified class were from the 51xx series (ex 31xx)and rebuilt into the 81xx class and retained the number 2 boiler, but again pressed to 225 p.s.i. as in the 61xx. Coupled wheels were of (yet another trifling reduced size)of 5' 6" diameter. These too had the 3' pony truck wheels. These were intended to bolster the 61xx class on London suburban duties with a supposed benefit of greater acceleration. Just how much difference the 2" variance actually made is open to question, given that wheels were designed to wear down by about that amount in normal service. Whatever the practical performance advantage, the class became widely dispersed and were used alongside their predecessors willy nilly.

Just ten of these engines were rebuilt from numbers 5100 (the 1903 remumbered prototype number 99), 5123, 5118, 5145, 5124, 5126, 5120, 5116, 5133 and 5115 and rebuilt as 8100 to 8109 respectively. In practical terms these were nothing more or less than the 61xx class with 2" smaller driving and pony truck wheels. In retrospect, these rebuilds seem somewhat superfluous cases of fiddling with proven designs, given that later new builds reverted to the more or less original 1905 specification and dropped the non standard driving wheel sizes and even (the likely more useful) higher boiler pressure.

The last forty locomotives constructed were additions to the 41xx series in the final years of the GWR and even into the second year of BR (WR) control.

Preservation. 10 engines of the 41xx/51xx series have been preserved. They are:- 5164, 5193, 5199, 4110, 4115, 4121, 4144, 4150 and 4160. The last three had very short careers in BR ownership, their time in preservation now easily represents the majority of their lives.

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