Fitting air brakes on locomotives

Pardon my ignorance, but what do diesel and electric locos use to produce their air supply - reciprocating or rotary? They also have the issue of varied demand to deal with. It seems to this inexperienced lay person that all this talk of turbines and the like overlooks the fact that a small reciprocating steam driven donkey engine might work just as well and with the advantage of being more flexible than most turbines.

Steve B

 

Steve, I'm not sure about heritage diesels, but modern electric units use electrically driven rotary compressors on each vehicle. You can hear them run up after a stop.

 

However if it becomes unpleasant for the support crew its possibly the case that you won't have the loco on the mainline in the first place - its all rather chicken and egg.

Would not adding the compressor to the support coach also add further complication and a weak spot to the system with the need for connection pipes between the coach and locomotive, having to run round with the coach or constantly switch systems if you separated locomotive and coach?

 

Have you ever fired a loco with a turbine fitted? The steam consumption is horrendous! A multi stage turbine with high pressure high temperature superheat driving a screw compressor will no doubt be superior to a reciprocating compressor, but not a single stage low pressure saturated steam turbine which is the sort of thing we fit to locos in the UK. The fact that the turbine would need to run at a fairly constant speed would require control gear to offload the compressor at working pressure which would be something else to go wrong. One advantage with up and down compressors is that the offloading gear is simple and if it fails then the compressor eventually stalls.

 

HI on are 1973 t/stock there is only two compressors fitted to a six car unit and only on the trailer cars. fit the compressor in to a
generator coach then plum in to the main line pipe. pdf file for air brakes on steam loco. FISH7373 81C

 

If one had the room it could be mounted underneath the solebar too.....
PS thanks for the attachment, very interesting.

 

When I'm support crewing I'd quite happily wear ear defenders to get some sleep instead of the loco being a failure. You could likely put the compressor far enough from sleeping areas for noise not to be an issue.

It would create a weak point but you'd only need an extra pipe that runs the length of both the loco and coach with connectors on each end. You might be able to tap it straight into the yellow main res pipe but I'm not sure if this would work. I've always thought axle driven compressors on the tender might be an avenue worth exploring, that way the westinghouse would only need to be used at the beginning of the day and after prolonged stops.

 

Modern compressors are much smaller and quieter, Does a ML loco need air to operate the loco brakes when running round when fitted with most normal duel braking systems or to operate any safety systems? if not then coach fitted compressors may be an option if an owner can not fit a Westinghouse pump to their engine without major work being needed of course Tangmere Could always use its pick up shoes to power a set when on 3rd rail

 

Last time Tangmere tried that, it didn't end well ...

Tom

 

It ended a darn sight better than if there hadn't been a conductor rail there.

 

All the safety gubbins (AWS, TPWS, etc) needs to be operational at all times and as that is usually in the air circuit, the answer would probably be yes.

 

It is feasible to have "dual braked" AWS/TPWS.
The outputs that energise the brake valve and horn valve/ yodel can, in theory, do both air and vacuum brake valves and air and vacuum horns. In theory.

 

I'm no expert in these things (far from it) but, as I understand it, you can have a vac/air system with vac as the prime system controlling the air or you can have an air/vac system with the air as the primary system controlling the vac. However, as vac/air proportional valves are like the proverbial rocking horse manure the usual is air/vac. Such equipment was fitted to the majority of diesel locos before the demise of vac.
If you have any spare vac/air valves, let me know!

 

HI have to dig out the braking system for the VAC/AIR one, the simple one to fit to a steam loco, vac/air valve is a DV2 D&M in the CLASS 47, best man for one of them is Kieth Nicholas of inter fleet. FISH7373 81C

 

A device whereby the vacuum train pipe proportionally controls the air brake pipe is a holy grail.
A number of people have tried to find out if such a valve ever existed, to no avail - so far......

 

HI
why would you want the VAC to put the AIR brakes on. the way is through M8 OR D&M brake handle to a DV2 is a AIR/VAC control valve that puts the air brake on loco and VAC brakes on the train, you can have a VAC only loco at front and second loco dual ed braked loco, in bitterns case the loco brake cylinders are air only but works VAC and AIR stock, and Britannia loco is VAC and STEAM brake cylinders only but can work with VAC/AIR braked stock. FISH7373 81C

 

Tornado is also an air braked loco with vac ejector and proportioning so can run vac or air-braked stock.

 

Britannia doesn't have a drivers vacuum brake valve any more. It has a westinghouse M8 to control air brake pipe and a DV2 to proportionally control the vacuum train pipe. It needs the vacuum ejector to run all the time to get proportional steam brake (loco & tender) control by the Gresham & Craven No4 steam brake valve.
Britannia could be fitted with the "air" body to the the G&C no 4, just like 73050. Then the vacuum would only need to run on vac trains.

Some people with vacuum only locos have thought about air braking, without filling the cab with a monstrous M8 contraption!

 

The original question was related to the possibility of having an air compressor in the support coach (post 49) and I said this wouldn't be practical as the AWS/TPWS would be on the air system. (Post 52) This provoked a question about the possibility of the AWS/TPWS being on the vac system instead and the vac operating the air brakes on the train. (Post 53). Whilst theoretically possible, it hasn't been done because the necessary kit (a vac/train pipe air proportional valve) is non-existent.