WAP5/WAG9 locos have a pneumatic system integrated with electronic controls, supplied by M/s Davies & Metcalfe. The systems in both classes are similar except for minor differences from their different brake riggings (Bo-Bo WAP5 vs Co-Co WAG9) and main-reservoir arrangement. Real reference documents: Scheme B1685 (WAP5 equipment layout), parts list B1685PL1, and the WAG9 schematics/parts-list Annexures 8.3/8.4.
Air Supply — Real Compressor & Reservoir Chain
Two real 2A320D electrically-driven air compressors feed through flexible hoses and 2 compressor check valves into the main reservoir system. Each compressor leg has a safety valve (protecting against check-valve blockage) and an unloader valve (operated by an electro-pneumatic valve on the brake frame). Compressors feed through a single water separator (with auto-drain, operated by the same unloader signal line) into two main reservoirs, each with a manual drain cock and an auto-drain valve (also unloader-signal-operated). Air then passes via a vented isolating cock into the twin-tower air dryer (giving significant dew-point depression), through a final filter (removing desiccant dust), then an isolating cock (a second, wired-closed bypass cock exists for air-dryer problems).
| Real Pressure Setting | Function |
|---|---|
| Compressor governor (single compressor, alternating mode) | Cuts between 10 kg/cm² and 8 kg/cm² |
| Compressor governor (both compressors together) | Cuts between 10 kg/cm² and 7.5 kg/cm² |
| Low main-reservoir governor | Interlocks with traction if MR pressure falls below its set point |
| Duplex check valve (MR-equalising-pipe feed to MR) | 5 kg/cm² — MR pressure must be at/above this before the valve feeds air, retaining air in the MR system if the equalising-pipe hose bursts |
| Brake-feed-pipe regulator | 6 kg/cm² — sets the control-part pressure for the relay valve feeding the brake-feed pipe on trailing 2-pipe stock |
| Automatic-brake relay valve amplification ratio | Approx. 1.44:1 (distributor signal to brake-cylinder output) |
| Dynamic-brake cut-out EP valve threshold | Energises (preventing duplicate braking) when dynamic brake exceeds 10 kN |
| Anti-slip valve build-up/release time | Rapid build-up ~1 second; long release ~20-30 seconds (to reapply power with some brake still present) |
The main-reservoir supply splits: one leg via check valve into a third 240-litre main reservoir (manual drain cock only), continuing via an isolating cock into the brake frame at port U, splitting to feed the direct-brake-valve pilot supply, brake-cylinder-cutout-valve pilot supply, direct-relay-valve MR supply, and blending-valve MR supply. The other leg enters via port W, splitting further — including via a duplex check valve into the main-reservoir equalising pipe (the through pipe linking one locomotive's MR to another's via hose/coupling/end cock) — letting one locomotive feed another's MR system if its own compressors fail, or letting a slave loco in a multiple consist help feed the lead loco under heavy air demand.
Real Sub-Systems Fed From the Main-Reservoir Equalising Pipe
- 'Break-in-two' protection valve: normally open, connecting the lead loco's direct brake valve to the direct brake pipe (or the slave loco's direct brake pipe to its relay valve) whenever MR-equalising-pipe pressure is present — but shuts this connection off if a 'break-in-two' occurs, ensuring a directed brake application remains possible on the locomotive.
- Sanding equipment: a direct feed to the pilot supply of 4 sanding EP valves, plus a choked supply to a reservoir, giving a rush of air to start sand moving in the sand injectors on valve operation, followed by a steady choke-metered flow for controlled sanding. Each of the 4 EP valves feeds one bogie-end combination (No.1-end/No.1-bogie, No.1-end/No.2-bogie, No.2-end/No.1-bogie, No.2-end/No.2-bogie).
- Anti-slip valves: energised when axle-set slip cannot be corrected by traction control alone, rapidly injecting air into the brake cylinders via a double check valve.
- Windscreen wipers and horns: fed via an inline strainer into each cab through vented isolating cocks; horn supply goes to a 2-way horn valve on each of the driver's and assistant driver's desks, each valve feeding both horns (one for forward, one for rearward handle movement).
Automatic Brake System — Real Function Chain
MR supply from port W feeds the flow meter, which supplies air to the direct brake valves (each cab) and to the E70 brake control unit. Any air demand from the direct brake or (more importantly) the E70 unit sets up a pressure differential across the flow meter, reducing pressure in the signal line to the flow meter valve — a high-gain pneumatic amplifier (a Venturi-based device) that turns a small pressure change into a large output-pressure change to the flow meter gauges, with a pressure switch sensing high-flow-demand conditions (e.g. a 'break-in-two'). E70 brake-control-unit charging/brake-pipe-pressure behaviour is detailed in real D&M catalogue A658/2. The brake pipe exits via an isolating cock with auxiliary switch contacts (raising an indication if inadvertently closed, since the brake pipe then won't charge) and passes out through port AA to the through automatic air-brake pipe connecting to other locomotives/trailing stock via hose/coupling/end cock.
The distributor responds to brake-pipe pressure variations against its own control reservoir, supplying a signal proportional to BP fall via the dynamic-brake-cutout EP valve to a volume reservoir and, via a double check valve, to the automatic-brake relay valve — an amplifier taking the distributor's signal and increasing it (approx. 1.44:1) out to the brake cylinders. On the distributor, an EP valve + limiter lets the driver operate a cab pushbutton (PVEF) to remove the locomotive's own automatic-air-brake application while still making a train brake application via the automatic brake pipe — inoperative during an emergency application, ensuring a locomotive brake application always occurs if emergency braking follows a full-service application where PVEF was used to remove it.
Parking Brake, Brake Blending & Direct Brake
- Parking brake: spring-applied, air-released, real chain — auxiliary reservoir → reducing valve (limits max. spring-brake-release-cylinder pressure) → latched solenoid valve (electrically controls apply/release on lead AND slave locos in MU, plus manual push-buttons for local operation whenever air pressure is present) → choke (restricts air loss from a burst parking-brake-feed hose) → bogie/actuator hoses → spring-brake port on the disc-brake actuators. Since release air comes from the auxiliary reservoir, a dead-hauled loco's brake-pipe feed into the auxiliary reservoir also releases its parking brake. A pressure switch indicates parking-brake applied/released status.
- Brake blending: the EBC/5 blending valve responds to the dynamic-brake equipment's signal (indicating required air-brake level, used in practice to bring air brakes to the same level as dynamic brakes if the dynamic brake fails), feeding via a check valve to the relay valve which supplies the brake cylinders.
- Direct brake: direct brake isolate valves are energised-to-close; on the lead loco, the isolate valve for the switched-on cab de-energises, letting that cab's direct brake valve feed the direct brake relay valve. Direct brake also feeds out via the break-in-two protection valve to the through direct-brake pipe for MU working; on a trailing loco, both isolate valves stay energised, blocking direct-brake-valve output from the cabs while still allowing the trailing loco's own direct brake to be applied via the lead loco.
Brake Cylinder Feeds, Pantograph Air & Auxiliary Supplies
- Direct-brake-cylinder pressure feeds each bogie via a choke through a double check valve (interfacing with the anti-slip valve and another double check valve for automatic-air-brake interface), a vented bogie isolating cock, a bogie hose choke, to the service-brake portion of the combined service/parking-brake actuators — operating through left/right-hand caliper sets onto brake discs. Wheel-tread conditioning units run off the same air supply as the service-brake cylinders.
- Pantograph equipment: normal-operation air comes from port W via a check valve into the pantograph reservoir, pilot-supplying the two-pantograph EP valve; air also passes via a vented isolating cock and port Q to the main circuit breaker; then via the 'Kabba' key-switch cock and pantograph EP valves to the roof (a throttle valve sits between brake-frame supply and the pantograph itself), with a pressure switch signalling air-supply status to the ABB central electronics. An alternative pantograph-raise air source exists if the loco has been stabled with no MR air present: an auxiliary compressor (governed by its own pressure switch, which stops it operating once MR pressure exceeds the switch's max. setting) feeds via a centrifugal strainer and check valve into the pantograph reservoir.
- Auxiliary air supplies: a sub-manifold on the brake frame's rear left supplies (via a reducing valve) 4 isolating cocks — 3 feeding electrical cubicles for traction control equipment, 1 feeding 2 EP valves for flange lubrication, which pump lubricant via nozzles to the external axle sets of the bogie.
Real Cab Instrumentation & End-Connection Protection
| Real Cab Gauge | Function |
|---|---|
| Gauge (MR/FP) | Indicates main-reservoir pressure (input to brake frame at port W) and brake-feed-pipe pressure (air-supply pipe for trailing vehicles) |
| Gauge (BP) | Shows brake-pipe pressure |
| Gauge (B.C1/B.C2) | Shows brake-cylinder pressure downstream of bogie isolating cocks, for both bogie 1 and bogie 2 |
| Flow meter gauge | Differential reading between MR pressure at port W and the flow-meter-valve output — indicates air demand on the automatic air-brake pipe, flagging heavy-flow events like a 'break-in-two' |
End-connection protection: dummy couplings house the coupling heads of hoses/couplings when the locomotive end isn't coupled. Vented isolating cocks on the headstock isolate the 4 through pipes if end cocks are damaged; the brake-pipe isolating cock specifically has a full-bore vent, so that if it's inadvertently closed on a trailing locomotive, the leading locomotive will be unable to create brake-pipe pressure on the locomotives or train — a deliberate fail-safe rather than a silent isolation.