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Author Topic: Landing-Craft accident, Railway Street, Chatham - 1953  (Read 135689 times)

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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #400 on: November 10, 2013, 08:40:42 »
The only drawing/diagram I have seen seems to have the air valve remote from the pedal............ The air valve seemed to be mounted on the passenger side of the front bulkhead, an ideal position for left hand drive with a direct pedal connection.

S4.
So needing an 'across the cab' linkage of some sort for right hand drive. Or would it not have been easier to move the air valve over to the right - all that would then be needed would be a different length air pipe to the brake cylinder?
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #399 on: November 09, 2013, 22:39:51 »
The only drawing/diagram I have seen seems to have the air valve remote from the pedal. More research needed. By 1964 they were building 'modern' units i.e. cab over engine. In these the air valve is directly connected to the pedal, there is no linkage. The drawing I have seen had the brake cylinder mounted just behind the cab operating the drums through rods. The air valve seemed to be mounted on the passenger side of the front bulkhead, an ideal position for left hand drive with a direct pedal connection.

We must remember that Scammel almost always ploughed their own furrow. Even when they were run by Leyland they were always 'different'. Like Foden and ERF they were always looked upon with affection by Drivers. Leyland became Leyland -DAF which is now DAF, ostensibly Dutch but most parts are built in the UK. I am happy to say that I drive a DAF, most look upon them as cheap and chearful waggon, Guv'nors Motors (reliable, fuel efficient, cheap on parts and easy to drive) but those of us who drive them know that they all have the heart of a Lion and just when you think there is nothing left they deliver a little more. Just like an old Scammel.........

S4.
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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #398 on: November 09, 2013, 21:51:01 »
From ‘Commercial Motor’, 9th October 1964:

Scammel Triple-line Brakes
To meet the new Regulations in respect of secondary braking, and to conform to the recently agreed standards by the S.M.M.T., Scammell Lorries Ltd. has designed a braking system for artic vehicles using the three-line system and having triple-diaphragm chambers at the front axle of the tractive unit and at the semi-trailer axle or axles.
The service brake operates in the usual way with a foot valve operating all axles of the outfit and a two-line system to the semi-trailer, whilst the emergency brake is hand controlled and operates the tractive unit front axle and, through a third-line, the semi-trailer axle or axles. A separate air-assisted mechanical handbrake operates the driving axle brakes.


Admittedly 9 years after this event, but  suggests that a ‘foot-valve’ was usual, rather than a separate pedal and valve
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #397 on: November 09, 2013, 16:47:32 »
I am trying to find out the braking arrangement of the Unit. Even with the web it is hard going......

S4.
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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #396 on: November 09, 2013, 16:19:24 »
Without knowing the exact arrangement of the braking system we never will lay this to rest, but the brakes would not have 'failed safe'. The only 'fail safe' feature is the spring brake applicators for parking brakes, wherein the brakes are held off by air pressure against a spring, and which I don't think existed in 1953.
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #395 on: November 09, 2013, 13:04:41 »
Today there are two air lines, one is sevice the other emergency. Should either fail then you still have control. Should both fail then you stop in a big hurry, personal experience here. I do not know how the old system worked but I guess that they failed safe, i.e. the brakes went on hard.

I feel that as you have worked out the fault was between the pedal and air valve, no argument there. Hence my question of the location of the aforesaid valve. As for the question about the pedal return spring I feel that it is almost important. If the valve is remote, as would seem, then there would be plenty of slack in the linkage. This would cause the pedal to rattle about. However with a return spring it would sit at the correct height for operation, and it would not rattle about as much. The initial application would take the slack then work the valve. The spring would also provide resistance and that impossible to describe 'feel'. However without a return spring should a pin fall out or a rod part then the pedal would fall to the floor as per Isaac Newton. The driver would have noticed that happening  and known that he had 'no pedal'. On the other hand with a return spring things would have been normal right up to the point he put his foot on the pedal and it went straight to the floor. That would give rise to his statement that the brakes failed.

I am sorry to all concerned that hoped and prayed that Peterchall and I had laid this to rest. I have a mind that is easily bored and recently have been thinking about a few items in this thread.

S4.
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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #394 on: November 09, 2013, 12:33:36 »
My comparison with air loss was unfair..........
Not if the trailer was braked, and a photo way back in the thread shows that army tank transporter trailers were. If so, the question arises as to whether the pipe between tractor and trailer could have been broken.

....I just wish to understand why and how he had a total loss of brakes.
Me too!
The problem is that web surfing only comes up with details of today’s systems, in which they all seem to have the pedal integral with the valve. But Clayton-Dewandre vacuum brakes of my young days had the vacuum cylinder way back on the chassis with long rods connecting the pedal to it, and I see no reason why that couldn’t apply to air brakes in those days, which would allow the possibility of the pedal becoming disconnected.

But I found a troubleshooting chart that includes the following problem:
Foot valve leaks at exhaust with foot brake applied
I imagine that, depending on the severity of the leak, it could cause partial or total brake failure and, just to be really helpful, the stated remedy is:
Replace foot valve

All I can find are rather complex diagrams showing a system of pistons and springs that uncover ports from the reservoir and to the brakes as they are pushed down by the pedal, thus applying the brakes – the spring system being to allow the pistons to ‘float’ to keep the braking effort proportional to the pedal movement. At the same time an exhaust port is covered by the pistons. When the pedal is released the pistons rise to cover the reservoir and brake ports and uncover the exhaust port, allowing air to escape from the brakes.

I can only assume that a broken spring somehow allows the piston to move so that air flows directly from the reservoir to the exhaust. No doubt very simple if someone sat down and explained it to me, but my brain’s not as young as it was….. :)
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #393 on: November 09, 2013, 08:48:39 »
My comparison with air loss was unfair. Today we have the fail safe that applies the brakes in the event of catastrophic failure. I really do not know enough about these older vehicles to comment on them. My thought with an older vehicle is how was the pedal connected to the air valve? Was it direct? Or indirect (via rods and joints). Was a return spring (to keep the pedal in a 'normal' position i.e. raised off of the floor) used? Or did the air valve keep the pedal raised?

I really have no problem with your hypothesis or postmortem, it all fits. I just wish to understand why and how he had a total loss of brakes.

Regards, S4.
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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #392 on: November 08, 2013, 22:37:21 »
Thanks for the compliment, but I'm still puzzled as to what, on the set-up as we assume it to have been, could have caused such sudden and complete failure. It could have been disconnection of the pedal due to a pin or bolt falling out, or failure of the foot valve. I only picked up the latter possibility from a table I found after some surfing.

I can explain the purpose of the foot valve - it is a two-way valve, passing air from the reservoir to the brakes when the pedal is applied, and from the brakes to atmosphere when the pedal is released. But I'm not familiar enough with it to describe how it can go wrong and only assume it fails by allowing air to go straight from reservoir to atmosphere when the pedal is applied.

It can't have been anything like what happened to you, unless the trailer was braked after all.
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #391 on: November 08, 2013, 18:15:47 »
Thank you Peterchall. I only wondered if the fail of a leather cup could be a contributor. You have, as ever, answered perfectly. A few years ago I had a fifth wheel lock fail and dropped the trailer, not very pleasant believe me. In doing so it ripped out all of the air lines. This was a catastrophic loss of air and the compressor could not keep up.

S4.
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Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #390 on: November 08, 2013, 11:45:25 »
Of course any sealing device can fail but our scenario depended on a sudden and complete brake failure.

Any flexible seal in brake cylinder, whether leather, rubber or synthetic, only closes the very small gap (a few thousandths of an inch) between the piston and cylinder so that even if it disintegrated completely the pressure would still act on the piston.

Unlike a hydraulic system, which would be defunct once all the fluid had leaked away, there would be a constant supply of new air from the compressor. The crucial factor would be if the compressor could keep up with the rate of leakage, and with the small amount of air that would leak past the piston, I’m sure it could.

I think all that would happen would be a very small reduction in the maximum pressure available.
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #389 on: November 05, 2013, 19:46:57 »
I know this is about 'done to death' but I have a question, maybe one for Peterchall. It concerns the air and hydraulic seals. I remember reading adverts in Practical Classics in the 1980's (showing my age here) for leather seals for brakes and such. I have also changed water pump plunger seals, also leather. I know that leather is a good seal, when lubricated, so could the air side have leather seals? Could one of these failing or starting to fail have caused the loss of brake effort that we all agree about? I think that this is worth a thought and might be the 'mystery' component that we all forgot about.

Regards, S4.
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Offline Sentinel S4

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #388 on: June 01, 2013, 21:59:57 »
I know the feeling Mickleburgh. I believe the term is 'Steering Wheel Attendant'............... :)

S4.
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Offline Mickleburgh

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #387 on: June 01, 2013, 16:01:14 »
My training for taking a PSV licence on a pre-war Leyland dd, long, long ago, was to ascend a hill whilst changing from top to bottom, without using the clutch and then to return down same hill, using brakes if need be, but changing down from top to bottom, again without using the clutch. It was not because one would ever need to do so in normal service but, I was informed, in order that the assessor could be confident I fully understood the vehicles workings and would be able to handle any situation. It is quite easy with a diesel engine, somewhat harder with petrol, but on one occasion when I called in a breakdown with a petrol Bedford coach saying the clutch rod had fractured, I was told bluntly to drive it home, twenty miles!
In more recent years, sitting at the controls of a modern 38-ton artic where engine revs, gear changing and everything else bar aiming it was controlled by computer, one sometimes felt as if you were only there for emergencies. Like an airline pilot it was nice to switch off the suto pilot on occasion and go back to manual flying!

Offline peterchall

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Re: Landing-Craft accident, Railway Street, Chatham - 1953
« Reply #386 on: May 30, 2013, 12:18:09 »
Smiler, I used the very scientific method of shutting my eyes and imagining myself as the driver – by the time I’d pumped the pedal a couple of times and then pulled on the handbrake, about 5 seconds had passed on my watch :). It was then a case of working out how far the unit would have travelled and how far to go with the handbrake on. (it is nothing more exotic than the formula ‘Final Speed = sq.root of initial speed squared + 2x accelerationxdistance’ – a few seconds work with a calculator, but imagine doing it back then, using log tables and long-hand arithmetic!!)). But you could be right, so I did the calculation again using 0 seconds and 10 seconds as the delay time and found that it makes no more than a couple of mph difference at the bottom of the hill – a longer time running free without the handbrake on is balanced by a shorter distance to go with it on, and so on.

What is important to make my scenario fit is that failure occurred near the top of the hill, otherwise there wouldn’t be time for the speed to build up enough for the unit to turn over. All I did was to make some, I hope reasonable, assumptions to work out the speed at which the unit would turn over, then work backwards from that to guess what could have happened to provide that speed

There are other scenarios, of course, such as the driver not even trying to use the handbrake, and until SentinelS4’s suggestion I had forgotten about the handbrake. But that is what ‘brainstorming’ is about – everybody throws in their ideas and, an essential requirement, everyone else picks holes in them until something clicks in someone’s brain and a fresh line of thought starts.
It's no use getting old if you don't get artful

 

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