manna wrote:G'Day Gents
There are three ways to 'Destroy' the brake on a vacuum braked carriage, 1- from the engine, 2- from the brake release cord, 3-from the communication cord, your rubber pipes probably connect to one of these, sorry can't help on any other tech bits
manna
Actually there are four ways of destroying vacuum in the train pipe, but pulling the communication cord isn’t one of them. That only reduces the vacuum to a point where the brakes start dragging (usually about 14 or 15 inches of mercury) in order to alert the driver. He then actually stops the train in a safe place of his own choice. It wouldn’t be a good idea for it to stop on a viaduct or blocking a junction for example, particularly since passengers seem to have a habit of getting off trains which have stopped in section.
The third way of destroying the vacuum is to take the back pipe off its “dolly”. I had to do that once at Dymchurch to a departing Down train, and the driver nearly shot out of the cab and over the boiler because the train stopped so quickly
The fourth way is the brake valve controlled by the guard. Using two methods simulataneously can be quite spectacular.
One afternoon, when on a guard duty, both the driver and I spotted sheep on the line ahead. He "downed" his brake handle at the same time as I opened my brake valve, and we stopped the train in about half its own length from 25 mph. It was as if the track had suddenly become and electro-magnet
I understand the basics of the automatic vacuum brake system well enough but I am pretty certain, though, that the LNER streamliner stock had quick service application valves fitted so that instead of air just being admitted just through the driver's brake valve, it was also admitted through these valves under the coaches when the driver braked. This ensured the trains could pull up that bit quicker than other trains. Indeed, testing a Coronation set fitted with these valves was the 'cover story' for the events of July 3rd 1938 with Mallard. Perhaps one of you technical types out there can describe how these valves worked and say if BR carried on with them, please - I think they may have adopted the idea?
try train divided as well and stretching a point -too low steam pressure on the engine. This is one time when a platform inspecter could climb into a cab to look at the pressure gauge to see there was enough steam.
keep 'em coming,
Jim Brodie.
direct application valves, when the vacuum dropped too low the valve in the guards van dropped out allowing a full application. We had such a valve on one of our NER Push Pull coaches. If you were going slow when it went then you stopped there and then and not where you wanted to
James Brodie wrote:try train divided as well and stretching a point -too low steam pressure on the engine. This is one time when a platform inspecter could climb into a cab to look at the pressure gauge to see there was enough steam.
keep 'em coming,
Jim Brodie.
Wouldn't be so bad if they knew what they were looking at. Direct admission or accelerator valves continued into BR and were also fitted to some freight stock.
An old inspector told me they'd get fitted trains down from Northampton at Market Harborough hauled by LNW super 'D's and the Midland engines couldn't blow the brakes off.
James Brodie wrote:try train divided as well and stretching a point -too low steam pressure on the engine. This is one time when a platform inspecter could climb into a cab to look at the pressure gauge to see there was enough steam.
keep 'em coming,
Jim Brodie.
Train divided will certainly stop the back portion which has separated from the rest of the train, which was the intention of the Regulation of Railways Act 1889 passed after the Armagh accident in that year. It won't stop the front part though because that will still be connected to the loco and its vacuum exhauster.
Low boiler pressure will gradually bring the brakes on. But how about a wonderful incident in Pakistan I remember reading about? There a brake hose on an end vehicle was left of its "dolly" over night and a rat climbed in. When vacuum was raised on the train the rat suffocated but its body blocked the pipe, so whilst the loco gauge showed a full vacuum the train was actually unbraked behind the corpse
A train division and parted vacuum pipes will stop the front portion of the train, ejectors/exhausters were not powerful enough to overcome that scale of leakage.
HQ1Hitchin asked for information about the quick acting valves introduced by the LNER.
The booklet "Vacuum Brake Instruction Book" published jointly by The Vacuum Brake Co.Ltd and Gresham & Craven Ltd has the answer.
(I believe that this publication was distributed to parties of M.I.C members attending demonstrations of the company's equipment)
The 'Direct Admission Valve' was fitted between the train pipe and the brake cylinder, and basically comprised a diaphragm coupled to an air admission valve.
Air is admitted to the brake cylinder in exact relation to the reduction of train pipe vacuum made by the driver.
The size of the Valve's air admission port is proportioned to suit the size of the brake cylinder, this ensuring even development of brake power throughout the train however mixed the stock may be.
A filter prevents dust being drawn into the system when the brakes are applied.
Sorry that I can't attach the full details and diagram, but am without scanning facility.
Sorry to resurrect an old thread but read some of the comments on this thread with a wry smile regarding ways to put a vac brake on and got me thinking back to a day working a Grimsby town FC special,
All were quite happily looking forwards to the game, including us as having been relieved we chose to continue on and watch the game but all was almost lost before we got there as having got back up to running speed from Wrawby junction all appeared normal until approaching Market Rasen when the brakes applied and we stopped, after several attempts to blow the brake off again we realised that all was not well behind so I set off on foot to examine the train.
First thought was maybe some disgruntled fan had pulled the cord so all the tabs had to be checked but none we out of alignment and all the 'Bags' were in place and we could get a partial vacuum of around 10" but not enough for a release, We had been there for a few minutes and of course things were getting a little heated in the train when after three trips up and down we had still not found the problem, it was on the train I was certain of that but were, after all Vac brakes were simple enough things with very little to actually go wrong after of the engine.
With the Guard meantime was trying to calm the fans as I went about the process of finding out which coach was at fault using the tried and tested methods when on the seventh coach we suddenly got vac back again meaning the eighth was the culprit, leaving me standing there looking at this thing trying to figure out why when I noticed something was missing, A complete brake cylinder and those things are not small, they normally have two, this only had one and a rather bent looking actuator rod next to were the second should have been,
It had simply fallen off the train taking with it the valve work and part of the rodding and at the same time tearing a fist sized hole in the metal brake line, which of course meant we would never get vacuum enough to work the train unless it was plugged, So asking one of the 'Faces' hanging out of various windows if anyone had a newspaper I grabbed a couple of lengths of bailing twine often seen hanging from fences line side and wrapped the paper around the pipe, Brakes came off and we were quickly under way again to Lincoln were we put the coach off for inspection and repair. We got there just in time for the kick off.
First and last time I ever went to a football match, first and only time I found a use for the Sun newspaper.
Hi all
I had a similar experience when working a loco hauled train from Carlisle to Newcastle, when we stopped at Haydon bridge ,I was unable to create the correct vacuum. I walked back with the guard and found a split on the small flexible pipe to the cylinder. We had nothing to hand to seal it. The guard asked if anyone had a plastic bag, a lady volunteered one which we fastened round the pipe with string, job done , no more problems ,on arrival at Newcastle we had a knock on the door,it was the lady asking if she could have her bag back. We referred her to the Station managers office who kindly supplied the said item. Since then I always carried a roll of insulating tape ,just to be safe.
