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Driving a DMU

General Information that a Driver SHOULD Know

(Compiled by Stan Acaster (Dean Forest DMU Group))

How would you couple up to another DMU?

Stop 6 feet away, wait till called by Shunter, proceed at idling until buffers touch, apply vacuum brake, release Deadman's, stop engines, remove C.I.S. and reverser, destroy high vacuum, place A.W.S. out of use, lock doors after extinguishing lights, see Shunter has coupled up correctly and inform Driver that everything is alright and all tools are removed.

How is an Engine and Final Drive Isolated?

Whenever engine is isolated, final drive must be isolated. Stop engines, turn engine isolation switch with carriage key, take isolating fork and walk round other side and pull out final drive isolation bolt from small slot and turn horizontal to long slot; go in cab and reverse two or three times, back down and see that bolt has gone home and that propeller shaft is free. With an electrical failure, engines must be stopped with the shut down solenoid, and dogs blown over by manually operating the F. & R. E.P.V. because there is not any electric current to operate with from cab.

With a final drive isolated the air and axle light will not illuminate as electrical connection is broken by the dog not being in mesh. The final drive to be isolated is always on the left when facing the defective engine.

How would you define Engines?

No. 1 is always on the L.H. side when sitting in the cab. No. 2 is R.H. side.

What Speed does Generator Charge Battery?

Generator vehicles at 17 m.p.h. maximum charge at 24 m.p.h., alternator vehicle charges at 550-600 r.p.m.

What are the Valves in the Air System?

Unloader valve, Safety valve, Reducing valve, Diverter valve.

What are their Purposes?

The Unloader Valve eases the load on the compressors by closing the valve from the reservoir and opening it to the atmosphere at 95 p.s.i. When the pressure falls to 80 p.s.i. in the reservoir the spring in the unloader closes the valve from the atmosphere and allows the compressor to pump air into the reservoir again.

The Safety Valve releases the air pressure at 98 p.s.i. when unloader valve is defective and blanked off.

What are the Valves in the Vacuum System?

Feed valve, Automatic Isolating valve, Deadman's valve, A.W.S. Isolation Flag, Communication Cord (P.C.V.), Emergency Brake valve, A.W.S. Emergency valve.

What is the Purpose of the Automatic Isolating Valve?

When both vacuum sides are destroyed this valve operates and isolates the high vacuum chamber allowing 19" to be kept in there. This saves a long wait in recreating vacuum after coupling to or uncoupling from another set.

What is the Purpose of the A.W.S. Emergency Valve?

When passing of a 'Dead' ramp, by the armature dropping, air is admitted underneath and lifts this valve, thus allowing air to rush through siren and pass through the valve and operate brake.

How many Electro-Pneumatic Valves are there?

4 Gear - G.1, G.2, G.3, G.4.
4 Throttle - T.1, T.2, T.3, T.4.
1 Forward, 1 Reverse.
All 'ON' types.

What is the Purpose of Electro-Pneumatic Valves?

When the valve solenoid is magnetized by selection in the cab, valve opens and allows air to enter its respective gears, or throttles, or directions, and operate them.

How many Types of E.P.V. are there?

Two, an 'ON' and 'OFF'.
The 'ON' type opens air valve when energised.
The 'OFF' type closes air valve when energised.

How would you test an E.P.V.?

Press button underneath valve and release. If air is released it is an electrical fault, if no air, it is an air failure or blockage. For forward and reverse E.P.V., reverser must be removed.

How is Reversing Achieved?

By means of a sliding dog clutch between bevel gears.

Why must Reverser be removed when starting locally or leaving cab?

Firstly, to save damage to dogs, which would be trying to engage bevel gear as air pressure was rising, through direction being selected. Secondly, if, for any reason, an unauthorised person gets into cab in your absence, no controls can be operated as desk is dead.

Prep and Basic Technique
General Info ->
Do's Dont's and Remembers
What do I do if...?
Fault Finding
Jumpers Disconnected

Driving a mechanical transmission DMU meant changing gears, those that had hydraulic transmission didn't (unless they were coupled to a mechanical DMU).

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