GW locos, vac brake problems.

[Swindon 123]

6 hours ago, The Johnster said:

 

Diesel and electric locos rely on a compressor to exhaust the vacuum, and some of the early ones were noticeably deficient compared to steam engines with long fitted trains; drivers had to learn new techniques to avoid losing time or even coming to a stand in sections.  This is one of the reasons for the adoption in the UK of a twin pipe air brake system, with a reservoir supply throughout the train to ensure a quick release of the brakes.  First generation dmus used a similar twin pipe vacuum system, and whatever else you might say about them the performance of their brakes in terms of both instant application and instant release even on long trains was superb.

I think you have got a bit confused with your braking systems there The Johnster. An exhauster on a loco creates the vacuum, and compressor produces compressed air. On a lot of diesel locos, two exhauster were fitted, as vacuum was the main form of braking when they were introduced. Exceptions to this that I came across were class 08's, some of which had two exhausters and some only one. ( A few had none at all). Class 46 locos only had one large exhauster, and I would suspect class 44/5 were also the same, but I'm not 100% sure. There may be others with only one exhauster, but I would never worked on them. I always found that as long as you never applied the vacuum below 10", recovering the brake using the exhauster speed up was never a problem. Make a brake application of below 10" vacuum, and releasing the brake always seemed to take a lot longer, hence I would never drop the vacuum brake below 10" when making a brake application if at all possible. The only twin pipe vacuum system that I worked with was on DMU's which had a reservoir pipe as well as the brake pipe, to air releasing the vacuum. The one weakness I found with DMU's was applying the brake was only done through the drivers brake valve, which meant it seemed like an age when applying the brake on a 9 car DMU set, although releasing it was a lot quicker. When you come to talking about the EQ vacuum brakes on deisel locos, that opens a whole new can of worms, with regards to applying the brake, which made a lot of noise, but seemed to do very little for a long time. Fortunately I didn't work many trains with locos that were EQ fitted. Another type of vacuum brake that you had to be very careful with was the DA, (direct admission) valves fitted to some wagons, which if not handled correctly would put you through the front windscreen on a loco. That's just the vacuum brake variations. i haven't even started on the air brake variations. nothing was ever simple on the railway.

 

Paul J.