The Class B17 is a sophisticated three-cylinder design, loosely developed from the earlier Class D49 4-4-0. It features piston valves and a round-topped boiler, characterized by the gracefully curved Gresley running plate and the nameplate positioned on the splasher over the centre driving wheels.
Cylinders and Valve Gear
The B17 utilizes Gresley Conjugated Valve Gear—a development of the Walschaerts system—where the motion for the centre cylinder is derived from the two outer cylinders. The outside cylinders drive the centre axle, while the inside cylinder drives the front axle.
Braking Systems
Due to its Great Eastern (GE) heritage, several locomotives were equipped with air brakes in addition to the standard vacuum system. For these engines, the air pump was located on the right-hand side adjacent to the smokebox.
| Loco Brake |
Train Brake |
Locomotives (BR Numbers) |
| Air |
Air or Vacuum |
61600 - 61615 |
| Steam |
Vacuum |
61616 - 61642 |
| Vacuum |
Vacuum |
61643 - 61672 |
Variants and Development
The class underwent several designations (B17/1, B17/4, B17/5, B17/6) as design improvements were implemented:
- B17/1: The original 1928 design, featuring a light axle load for East Anglian lines and small GE-style tenders for short turntables.
- B17/4: Introduced in 1936 with larger LNER-style tenders for longer journeys on the Great Central section.
- B17/5: A purely cosmetic variation featuring a streamlined appearance similar to the A4 Pacifics.
- B17/6: The final improvement, featuring the powerful 100A diagram boiler.
- Class B2: A rebuild by Edward Thompson into a two-cylinder locomotive, essentially a B1 with larger driving wheels.
Technical Data: Core Class Details
| Locomotive Dimensions |
Mechanical Configuration |
| Wheels |
4-6-0 |
Cylinders |
Three |
| Piston Diameter |
17 ½” |
Valve Gear |
Gresley conjugated |
| Piston Stroke |
26” |
Valve Type |
Piston |
| Driving Wheels |
6’ 8” |
Superheated |
Yes |
| Loco Weight |
77 tons 5 cwt. |
Driving Position |
Left side |
Variant Specifications
B17/1 (Original 1928)
| Traffic |
Mixed Traffic |
| Boiler Pressure |
180 psi |
| Tractive Effort |
22,485 lb. |
| BR Power Class |
4MT |
| GE Tender Weight |
39 tons |
B17/4 (1936 Design)
| Traffic |
Mixed Traffic |
| Boiler Pressure |
180 psi |
| Tractive Effort |
22,485 lb. |
| BR Power Class |
4MT |
| LNER Tender Weight |
52 tons |
B17/6 (100A Boiler)
| Introduced |
1943 / 1947 |
| Boiler Pressure |
225 psi |
| Tractive Effort |
28,555 lb. |
| BR Power Class |
5P4F |
| Tender Weight |
39t 6cwt (GE) / 52t (LNER) |
Class B2 (Thompson Rebuild)
| Cylinders |
Two |
| Boiler Pressure |
225 psi |
| Tractive Effort |
24,865 lb. |
| BR Power Class |
5P4F |
| Introduced |
1945 |
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