BSI Couplings - 156 Super-Sprinter

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156422+156418 cab to cab.20.July.2002

156422 coupled to 156418 at Nottingham on 20.July.2002.

Automatic Couplings

The use of automatic couplings allows units to join to form longer trains, or to detach portions, without the need for shunting staff on the track. It is therefore quicker and safer.

Since the mid 1970s British Rail had been using 'Tightlock' automatic couplings on EMUs, and these had also been used on some of the Railbus units built in the early 1980s.

A smaller low-weight design, the 'Compact' produced by Bergische Stahl Industrie (BSI), had first appeared in the UK on the Metro-Cammell built trains for Tyne & Wear Metro in 1978.

When BR's Provincial Sector drew up a specification for it's replacement DMU fleet, it standardised on the BSI Compact coupling, with a CK2 type head.

Prototype Sprinters 150.001/2 and 151.001/2 were the first to feature BSI couplers (although as built, they had an additional brake pipe connection on the coupler head and were incompatible with later build units).

The post-privatisation class 170s 'Turobstars' feature Compact couplings to allow compatiblity with the 15X Sprinter fleet, although the class 156s required a minor wiring alteration before they could work with 170s.

Other recent builds of UK Multiple Unit have used 'latch-type' couplings from Scharfenberg and Dellner.

BSI Compact coupling

The Compact is a centre buffer coupling which takes all traction and buffing loads, therefore side buffers are not provided.

The coupling heads are integral with the drawbar. The design is such that there is no freedom of movement between couplers when connected, and all relative movements between vehicles are accommodate at the drawbar pivot.

In the event of a unit failure, assistance by locomotive is possible with an emergency adapter coupling (which is carried on board some units).

BSI coupler, right side (class 156)

The Compact coupling comprises of 3 parts: Pneumatic, Mechanical and Electrical.

  • Top: Air connection block, with the Main Reservoir Pipe coupling in the centre

  • Middle: Coupler Head, with Coupler Pin, and Pocket.

    On the lower right is the Gathering Horn, which guides the coupling heads into alignment.

    To the right of the pocket is the Uncouple Latch-Pin.

  • Bottom: the Electrical Connection Box with its cover closed.
BSI coupler, electrical interconnector (class 158)

The Electrical Connection Box has a cover to protect it from dirt.

When opposing couplers engage, the cover rolls open to allow the electrical contacts to connect.

There are 50 fixed pins on the right side, and 50 moving pins on the left side, plus 3 more in the centre.

Sprinters use only 42 'train wires', so 11 pins are spare.

BSI coupler, left side (class 156)

On the left hand side is the Uncoupling Mechanism.

When the Uncouple button is pressed in the cab, an air-powered piston pushes the uncoupling lever outwards, causing the coupling pin to be retracted.

The forward spike on the uncoupling lever should be held in position by the Latch-Pin on the opposing coupler until the units have separated.

If units with incompatible or defective couplings need to be coupled to clear the line, the electrical connection boxes can be retracted using the 'tommy bars' provided on each side of the coupling.

156404, SVR diesel weekend, 7.May.1988

Cab-End Couplings

In addition to the automatic coupling, the cab ends of units also have:

  • an electrical jumper socket (orange colour, right).
    This enables 3-car sets to be formed.

  • an emergency air supply 'Schrader Socket' (red colour, left). Allows an assisting locomotive to restore main reservoir pressure should this be required.
156.404 in 1988, without obstacle deflectors, showing the cab end couplings to advantage.

Photo: Steve Jones

BSI coupler, inner-end (class 156)

Inner-End Couplings

The couplings at the intermediate ends of units are semi-automatic.

They have only mechanical and pneumatic couplings, therefore a separate 42-way electrical jumper cable is provided.

Uncoupling is done manually using the uncoupling lever.

Gangway Connections

Class 156s are gangwayed at both intermediate and cab ends. The gangway opening is 550mm wide.

Each gangway is suspended by 6 'flexitors'. There are 2 large flexitors either side of the gangway at floor-height, 2 smaller ones which are attached to the drawbar and move the gangway when the coupler moves, plus 2 more inside the top of the rubber gangway shroud.

The faceplate of the gangway has anti-friction pads affixed to the right hand side and a lamp bracket is provided on the left hand side.

Coupling and Uncoupling

The coupling and uncoupling of units is fully automatic, under the control of push buttons in the driving cabs.

Procedure for attaching units:

Procedure for detaching units:

non-multi sign156485 (non-multi) 27.Mar.04

Non-Multi Restriction

Units can be used in service with defective autocouplers.

To warn staff not to attempt to couple units together in multiple, a 'non-multi' sign (a yellow rectangle with a black X) is displayed in the secondman's cab window at the defective end.

156.485 photographed at Stirling showing the 'non-multi' sign in the cab of 57485 on March 27, 2004.

156478 with Coupler Bag

156.477 and 478 at Inverness, circa 1999.
Photo: Roderick MacNeil

Coupling Bag

In cold weather a plastic or canvas cover, known as the coupling bag, can be tied over the autocoupler to prevent snow or ice building up.

The disadvantage of using the coupling bag is, if units need to be coupled together, a member of staff must go on to the track to remove it.

The coupling bag is sometimes used 'out of season' on units with defective couplers.

emergency coupling
Photo: P. Clay

Emergency Coupling Adaptor

In the event of a total unit failure, assistance by locomotive is possible with an emergency adapter coupling (which is carried on board some units).

The preference will always be to use a mutiple-unit with compatible couplings for assistance, so use of the emergency couplings is very rare.

There have been some occasions where a BSI fitted DMU has used an Emergency Coupling Adaptor to haul a dead Electric Multiple Unit.

emergency coupling

With no brake continuity between the assisting locomotive and the failed DMU, the combined train must not exceed 10mph, and the driver of the failed DMU must be ready to apply the brake if necessary.

If the DMU vehicle is not able to maintain its own air supply, a hose connecting the assisting locomotive's main reservoir pipe to the DMU's 'Schrader Socket' can be used. The photograph shows class 37 locomotive 37676 coupled to vehicle 57499 in June 2010, after a derailment near Falls of Cruachan.

Air Coupling Coupler Pin Coupler Head Air Connection Block Electrical Connection Box Uncouple Mechanism Tommy Bar Main Reservoir Air Pipe Uncouple Piston Air Supply Coupling Suspension Unit Electrical Jumpers Gangway Faceplate Uncoupling Latch Pin Gathering Horn Coupler Pocket Drawbar Obstacle Deflector Air Coupling Electrical Contacts - Fixed Electrical Contacts - Moving Guide Horn Uncouple Mechanism Coupler Head Air Connection Block Coupling Pocket Electrical Coupling Cover Electrical Connection Box Electrical coupling cover Electrical Connection Box Air Connection Block Main Reservoir Air Pipe Tommy Bar Microswitch Uncouple Piston Uncoupling Lever Uncouple Mechanism Main Reservoir Air Pipe Coupler Suspension Unit Gangway Support Bracket Obstacle Deflector Electrical Jumpers Drawbar Gangway Faceplate Autocoupler Emergency Air Connection Electrical Junction Box Warning Horn Box Coupler Suspension Unit Lamp Bracket Gangway Faceplate Electrical Jumper Socket