British Rail Class 144

British Rail Class 144 Pacer
Northern Rail/WYPTE Metro Class 144 Pacer No. 144001, recently reliveried, is seen at Sheffield
The refurbished interior of a Northern Rail Class 144
In service	1986–present
Manufacturer	British Rail Engineering Limited, Derby Walter Alexander
Order no.	31015 (DMS) 31016 (DMSL) 31037 (MS)
Family name	Pacer
Constructed	1986-1987
Entered service	1986
Refurbishment	2002 - 2004 and 2010
Number built	23 trainsets
Formation	DMS(+MS)+DMSL
Diagram	DP240 (DMS) DP241 (DMSL) DR205 (MS)
Fleet numbers	144001-144023 (sets) 55801-55823 (DMS) 55850-55859 (MS) 55824-55846 (DMSL)
Capacity	99 or 157 seats per unit
Operator(s)	Northern
Depot(s)	Neville Hill
Line(s) served	Harrogate Line Huddersfield Line Hallam Line Penistone Line Pontefract Line York & Selby Lines Caldervale Line
Specifications
Car body construction	Steel underframe. Aluminium alloy body and roof.
Car length	15.093 m (49 ft 6.2 in) (DMS, DMSL) 15.186 m (49 ft 9.9 in) (MS)
Width	2.695 m (8 ft 10.1 in)
Height	3.725 m (12 ft 2.7 in)
Floor height	1.288 m (4 ft 2.7 in)
Doors	Twin leaf pivot
Articulated sections	3 (144001-013) 2 (144014-023)
Wheelbase	9 m (29 ft 6 in)
Maximum speed	75 mph (121 km/h)
Weight	24.17 t (23.79 long tons; 26.64 short tons) (DMS) 25.04 t (24.64 long tons; 27.60 short tons) (DMSL) 23.5 t (23.1 long tons; 25.9 short tons) (MS)
Prime mover(s)	Cummins LTA10-R (Originally fitted with Leyland TL11 6-cylinder 11.1-litre)
Engine type	10-litre
Cylinder count	6
Power output	Cummins: 225 hp (168 kW) at 2100 rpm Originally Leyland: 205 hp (153 kW) at 1950 rpm
Transmission	Mechanical, self-changing gears
Train heating	Engine waste heat Ducted warm air
Braking system(s)	Air
Safety system(s)	AWS TPWS
Coupling system	Automatic BSI (outer) Bar (inner)
Multiple working	Class 14x, 15x and 170
Track gauge	1,435 mm (4 ft 8 1⁄2 in) standard gauge

The British Rail Class 144 Pacer diesel multiple units (DMUs) were built by British Rail Engineering Limited, Derby from 1986 to 1987. A total of 23 units were built, replacing many of the earlier first-generation "Heritage" DMUs.

At the beginning of the 1980s British Rail (BR) had a large fleet of ageing "Heritage" DMUs, built to many different designs in the late 1950s and early 1960s. Some of the more reliable types were retained and refurbished. However, BR decided to replace many of the non-standard or unreliable types with new second generation units, built to modern standards. Two different types were pursued; low-cost "Pacers" built using bus parts and used on short-distance services; and "Sprinters" built for longer-distance services.

Twenty-three Class 144 units were built. The units have a maximum speed of 75 mph (121 km/h) and are externally similar to the earlier Class 143 Pacers (they have a Walter Alexander body like the Class 143), built in 1985–1986. The first thirteen of the class, No. 144001-013 are 2-car units. The remaining ten, No. 144014-023 are all 3-car units, although all were originally built as 2-car units, the centre vehicle being added later. These ten Pacers are the only Pacers to contain intermediate vehicles.

Units are formed of two driving motors, one of which contains a toilet. The 3-car units have an additional intermediate motor. All vehicles have standard-class seating only. The technical description of the formation is DMS+(MS)+DMSL. Individual vehicles are numbered as follows.

The Class 144 units have BSI couplers. This allows them to work in multiple with Class 142, Class 143, Class 150, Class 153, Class 155, Class 156, Class 158, Class 159 and Class 170 units, as well as units of the same class.