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4400 / 4500 tank classes introduction

Running numbers: 4400 - 4410, 4500 - 4599, 5500 - 5574.

Built:     1904        (4400) to lot number 144,
            1905-06   (4401 - 4410) to lot number 147,
            1906-08   (4500 - 4519) to Wolverhampton lot number N3,
            1909-10   (4520 - 4529) to lot number 174,
            1913        (4530 - 4539) to lot number 191,
            1914-15   (4540 - 4554) to lot number 201,
            1924        (4555 - 4574) to lot number 226,
            1927        (4575 - 4599, 5500 - 5504) to lot number 242,
            1927        (5505 - 5524) to lot number 249,
            1928        (5525 - 5544) to lot number 251,
            1928-29   (5545 - 5574) to ot number 253.

        As an extension to the large Prairie tanks first produced in 1903, a prototype, number 115, '4500' class number 5541 on the Dean Forest Railwaywith smaller dimensions was built in 1904 to work the hilly branch lines of the West Country and Wales. Equipped with driving wheels of 4 feet 1½ inches, a smaller boiler than the large prairie and cylinders of 17 inches diameter by 24 inches stroke, she was an immediate success and less than a year after its introduction, a further ten locomotives were ordered on a Swindon lot number but actually built at Wolverhampton. The class became numbers 3101 - 3110 for a short time until renumbered 4401 - 4410 with the prototype renumbered 4400.

        When additional locomotives were required, it was felt that the driving wheel diameter was rather small for any fast running and so limiting their use. Further orders utilised the larger 4 feet 7½ inch driving wheels giving the engines a far greater range. The first batch of 20 locomotives were built Bunker design of '4500' class number 5572at Wolverhampton and numbered 2161 - 2180, whereas the next batch numbered 2181 - 2190, and all of the series built afterwards were produced at Swindon. Renumbered in December 1912 as 4500 - 4529, these engines were fitted with the square front framing while engines produced after number 4530 had the curved framing although, similar to the 2800 class, due to the low height of the running plate the curve was not as pronounced as other models.

        The 4500 series can be divided into two separate classes: the 4500 class consisting of 4500 - 4574 which had the flat topped tanks, and the 4575 class from 4575 to 4599 and 5500 to 5574 which were fitted with the increased capacity sloping topped tanks.


Modifications.
        Number 4555 onwards'4500' class number 5572 showing the cab and sloping tank were fitted with outside steam pipes and lengthened frames at the rear as standard. Some previous members of the class were also modified but not all.

        Again similar to the 2800 class, smokebox struts were used to support the front frame extension from 1909.


Withdrawal.
        The first withdrawal of the 4400 class was in December 1949 of number 4402 while three engines survived until September 1955.

        Of the 4500 class, the first withdrawal was of number 4531 in February 1950 and the last in service until September 1964 was number 4564.

        Regarding the 4575 class, first withdrawn was number 4586 in April 1956 and the last four locomotives of the class were withdrawn in December 1964.


Preservation.
        Three members of the 4500 class and eleven members of the 4575 class were saved from the cutters torch and they are numbers 4555, 4561, 4566, 4588, 5521, 5526, 5532, 5538, 5539, 5541, 5542, 5552, 5553 and 5572.


Specifications (4500 series with superheater).

Cylinders (2) 17 x 24 inches Driving wheel diameter 4 feet 7 inches
Bogie / Trailing wheel dia 3 feet 2 inches Tractive Effort 21,250 pounds
Water tank capacity 1,300 UK gallons Boiler maximum dia. 4 feet 9 inches
Boiler minimum dia. 4 feet 2 inches Fire tubes, no. and dia. 196 x 1 5/8 inches
Flue tubes, no. and dia. 6 x 5 1/8 inches Superheater tubes, no. and dia. 36 x 1 inch
Boiler pressure 200 lbs/square inch. Boiler length 10 feet 6 inches
Area of firegrate 16.6 square feet Heating surfaces, tubes 992.51 square feet
Heating surfaces, firebox 94.25 square feet Heating surfaces, superheater 73.8 square feet


    

Details: 4500 tank class, 4400 to 4410    Details: 4500 tank class, 4500 to 4574     Details: 4575 tank class, 4575 to 5574

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