Originally, boiler barrels were usually telescopic, having two or three rings, with their diameters reducing (usually, but not always) from firebox end to smokebox. The sizes quoted were for the barrel length and diameter over the rearmost ring.
The firebox casing length was quoted, but not usually the width because Stirling had standardised this at 4ft.-0½in. (a requirement for frames set 4ft.-1½in. apart), and this remained the standard to the end of steam. Although some of Stirling’s boilers for Sturrock rebuilds were 4ft.-0in. wide, these were fast disappearing. Also the fireboxes in his 8-foot singles were 3ft.-11½in. wide, as their frames were 1in. closer together than usual. Ivatt then introduced a new exception with his Broad Grate (BG) Atlantics, which had 6ft.-9in. wide firebox casings.
Ivatt quickly changed the 3-ring barrel designs to be 2-ring, except on his larger boilers. Later Gresley introduced 1-ring barrels for the small boilers, and also introduced the slightly tapering 1-ring barrel, to avoid the cost of making slightly larger diameter smokeboxes.
Details such as tube sizes and diameters, working pressures, tended to be ignored, as these could change in an individual boiler during its lifetime.
The following lists the boiler types built from 1896 onwards and mentioned in the Boiler Order books, and so includes some Stirling examples without domes, which continued to be built during the Ivatt period. The types are listed in order of first appearance of a particular type, with a cross-reference to the appropriate first relevant Boiler Order, first engine fitted, and LNER Boiler Diagram where appropriate
Only purely Doncaster-type boilers are shown, thus NER and GER based, LMS designs, and BR Standard designs are excluded. Also excluded are Stationary Boilers. Dgm. 100A is however included as its origin (Dgm. 100) was not a Gresley-Doncaster product (which would have been one very good reason for Thompson choosing it as his standard boiler). Variations of 3-ring, 2-ring and 1-ring barrels are quoted. But variations such as Dgm.s 94HP, 94A, 96A and 113 are ignored as the basic dimensions of the shell are the same as in the original design (i.e. Dgm.s 94, 96 and 112).
The barrel diameter quoted is the one measured over the ring at the firebox end, which is not necessarily the largest diameter ring.
For engines with a sloping throat-plate at the front of the firebox casing (effectively providing an extra combustion chamber), the length of the firebox casing measured at the bottom plus the length of the barrel no longer equalled the overall length of boiler. In such cases it was the usual practice to quote the length between smokebox and firebox tube-plates. So, in the Table, the barrel length shown for Boiler Dgms. 94, 100A, 106-09/11-13/15-18 is in fact the distance between tube-plates.
| Barrel diam | Barrel length | Firebox casing length | Barrel rings | First engine | LNER Dgm. | First appeared | First BO |
|---|---|---|---|---|---|---|---|
| 4′-2″ | 11′-3″ | 6′-8″(a) | 2 | 93 | – | 6/1896 | – |
| 4′-5″ | 10′-1″ | 5′-6″ | 3(p) | 1021 | 11 | 2/1896 | – |
| 4′-5″ | 10′-1″ | 5′-6″ | 2 | 400 | 11 | 12/1896 | 400E |
| 4′-5″ | 10′-6″ | 5′-6″ | 2 | 1201 | 9 | 3/1897 | 203 |
| 4′-2″ | 11′-5″ | 6′-2″ | 2 | 873 | – | 4/1898 | 204 |
| 4′-0½” | 10′-1″ | 5′-6″ | 3(p) | 601 | – | 5/1897 | 205 |
| 4′-0½” | 9′-3″ | 4′-6″ | 3(p) | 632 | – | 5/1897 | 501 |
| 4′-8″ | 14′-85/8“ | 8′-0″ | 3 | 990 | 4 | 5/1898 | 502 |
| 4′-8″ (b) | 10′-1″ | 6′-4″ | 2 | 1321 | 7 | 6/1898 | 505 |
| 4′-5″ | 11′-4″ | 7′-0″ | 2 | 266 | – | 10/1898 | 506 |
| 4′-2″ | 11′-5″ | 6′-2″ | 3(p) | 94 | – | 5/1898 | 507 |
| 4′-5″ | 10′-1″ | 4′-10″ | 2 | 118 | – | 10/1899 | 512 |
| 4′-0½” | 9′-10″ | 4′-10″ | 3(p) | 124 | – | 2/1899 | 513 |
| 4′-0½” | 9′-10″ | 4′-6″ | 3(p) | 162 | – | -/1899 | 513 |
| 4′-8″ (c) | 10′-1″ | 6′-4″ | 2 | 1336 | 7 | 9/1899 | 519 |
| 4′-0½” | 10′-6″ | 5′-6″ | 3(p) | 928 | 9/1900 | 523 | |
| 4′-8″ | 15′-4¼” | 8′-0″ | 2 | 271 | 4 | 7/1902 | 530 |
| 4′-8″ | 14′-85/8“ | 8′-0″(d) | 3 | 401 | 4 | 2/1901 | 531 |
| 4′-2″ | 10′-6″ | 6′-2″(a) | 3 | 116 | – | 8/1903 | 537 |
| 5′-6″ | 15′-63/8“ | 6′-6″(e) | 2 | 251 | 1 | 11/1902 | 546 |
| 4′-2½” | 10′-1″ | 5′-6″ | 2 | 765 | – | 12/1904 | 568 |
| 4′-2″ | 10′-6″ | 6′-2″ | 2 | 117 | – | 8/1904 | 555 |
| 4′-0½” | 3′-8″ | 3′-6″ | 1 | RM2 | – | 10/1905 | 244/1 |
| 5′-6″ | 15′-63/8“ | 6′-6″(f) | 2 | 1421 | 1 | 4/1907 | 573 |
| 4′-8″ | 10′-1″ | 5′-6″ | 1 | 1163 | 8 | 5/1912 | 608 |
| 4′-8″ | 10′-1″ | 6′-4″ | 1(h) | 71 | 7 | 8/1912 | 609 |
| 4′-8″(b) | 11′-8″ | 8′-0″ | 2 | 1630 | 6 | 8/1912 | 610 |
| 5′-6″ | 15′-5½ “ | 9′-6″ | 2 | 456 | 2 | 12/1913 | 616 |
| 5′-6″ | 11′-5½” | 8′-6″ | 2 | 420 | 3 | 2/1914 | 618 |
| 6′-0″ | 11′-5½” | 9′-6″ | 1 | 1000 | 96 | 3/1920 | 648 |
| 6′-5″ | 19′-0″ | 9′-5½”(g) | 2 | 1470 | 94 | 4/1922 | 653 |
| 4′-5″ | 10′-6″ | 5′-6″ | 1(j) | 4231 | 9 | 9/1927 | 703 |
| 4′-5″ | 10′-6″ | 5′-6″ | 1(k) | 4228 | 9 | 5/1929 | 737 |
| 5′-0″ | 11′-10″ | 7′-2½” | 1 | 2900 | 102 | 9/1930 | 750 |
| 6′-5″ | 18′-11¾” (m) | 10′-9″ | 2 | 2001 | 106 | 5/1934 | 801 |
| 6′-5″ | 17′-11¾” | 10′-5¾”(g) | 2 | 2509 | 107 | 9/1935 | 821 |
| 6′-5″ | 17′-0″ | 9′-5¾” | 2 | 4771 | 109 | 6/1936 | 822 |
| 6′-5″ | 17′-11¾” (m) | 11′-9″ | 2 | 2006 | 108 | 9/1936 | 823 |
| 6′-5″ | 17′-11¾” | 11′-9″ | 2 | 10000 | 111 | 11/1937 | 834 |
| 5′-4“ | 13′-6″ | 8′-9″ (k) | 2 | 3401 | 112 | 2/1941 | 861 |
| 5′-6″ | 13′-117/8“ | 9′-0″ | 2 | 8301 | 100A | 12/1942 | 891 |
| 5′-0″ | 11′-10″ | 8′-0″ | 1 | 9000 | 115 | 5/1945 | 911 |
| 5′-6″ | 11′-9″ | 10′-1½” | 2 | 3445 | 116 | 12/1945 | (n) |
| 6′-5″ | 17′-0″ | 11′-41/8“ | 2 | 500 | 117 | 5/1946 | 914 |
| 6′-5″ | 16′-115/8“ | 11′-41/8“ | 2 | 525 | 118 | 12/1947 | 923 |
(a) Firebox casing width was 3ft.-11½in.
(b) Diameter over the front ring was 4ft.-91/8in.
(c) Front ring now smaller in diameter than rear one.
(d) Shallow firebox to clear rear coupled axle.
(e) Broad grate. Firebox casing 6ft.-9in. wide.
(f) Broad grate and deep firebox.
(g) Broad grate. Firebox casing 7ft.-9in. wide.
(h) First 1-ring Dgm. 7.
(j) One parallel ring.
(j) One ring, tapering down to smokebox end.
(k) Broad grate.
(m) 2ft-0in shorter barrel after rebuilding (1943/44).
(n) This was a Gorton-built Dgm. 100A boiler, altered at Doncaster to Dgm. 116, and then fitted to No. 3445.
Later, Doncaster did build a few Dgm. 116 boilers for spares.
(p) Domeless boilers