Weekend Rails

what we do for our kids

Of thinking and spraying

12th August 2018

You just cannot underestimate the power of the written word. Only last week I declared my dissatisfaction with the on-going heat and look! It's been raining today, we've had to have the lights on in the shed and I nearly took a sweater down with me. So, what if I declare that this week I'll win the lottery? Aah, hang on, I've seen a snag in that. I don't play.

Despite there not being a Monday occupied at Tunstead I seem to have spent even more time and money on RS8 this week. First there was the obvious, draw up in CAD the instruments you saw pictured, rough out the desk sizes and lay out the instruments to see how best they fit. The upshot is that I now have a preliminary panel design, complete with piano hinge, side walls and profile drawing ready to go. But it is as yet preliminary in that I want to go over it one more time and check the dimensions on the loco before I commit.


On the original control system, RS8 had two identical Lang valves that operated Clutch and Direction. You can see what was left of them in the picture. The Direction control was modified with a paddle that went down below the desk top through a slot, and underneath was a midget cylinder that locked it in one position or the other. Now, although the basics of any Twin Disc converter drive loco are essentially the same – you have an over-centre clutch between engine and converter and after it a final drive reversing gearbox, both clutch and gearbox being operated by pneumatic cylinder(s) – every manufacturer has their own way of achieving it. Well that's not quite true, because so far as I can see, Planet and Fowler tended to buy an off-the-shelf system from Westinghouse, but after that, there are crucial differences. Hudswell, on their 0-4-0DHs like Claire, Beverley and Grace, made their own clutch cylinders with a massive piston rod that created a differential in force between either side of the piston. The smaller one was continually fed with main air and put the clutch 'out'. The bigger side was fed with the same pressure when you wanted the clutch 'in' and the larger surface area created a greater force and pushed the 'out' side air away. Sentinel, like Hunslet, Hills, and so on, used 'standard' industrial cylinders (except that until the VDMA compelled pneumatics manufacturers to make a common sized cylinder, there was no such thing as standard) but having been told by steam loco drivers that the ability to reverse the loco in motion was essential, did the next best thing and came up with a pre-select gearchange system that is a swine to fault-find.

Anyway, RS8's employed a locking cylinder linked to the standstill detector to prevent you changing direction unless the loco is standing still, but it's not the only way to do it and in this day and age I would probably be told that I need a safety guard to prevent finger-trapping! To release the lock, incidentally, required the operation of a push button, and there were two of these, one at each side of the cab, which seemed to me a trifle odd with the control lever being right in the middle – a bit of an inconvenient combination, though the drawings show a footpedal was the original idea (Yorkshire did it like that). The clutch control too, is a trifle dodgy. First off, most locomotives have some means of preventing you putting the clutch 'in' with the engine revving furiously – it's downright dangerous and doesn't do clutch, converter or gearbox any good at all. Usually it is by having the throttle lever in the idle position or beyond, whereupon a roller operated valve is toggled – Sentinel and EE did it this way and Hills detected the linkage in the idle position. Of course, having the throttle lever at idle doesn't prove that the engine revs are at idle, not easy pneumatically or mechanically but a doddle electronically nowadays, but RS8 had nothing. Similarly it is a golden rule that you must NOT leave the force applied to the clutch linkage having put the clutch 'in', so there must be either a pneumatic unload, or when air pressure must be maintained, as on the Hudswell system there is a mechanical stop which is set up to take the force off the linkage. Why? Well if you leave it applied, it causes excessive wear to all the pins and pivots. RS8 had no such system, and despite a cylinder far smaller than I have ever seen, a significant cost of the converter overhaul was caused by having to renew all the clutch linkage parts through wear. So I've been doing some head-scratching this week on the control system and whether or not I can do away with that slot and locking peg and maybe make the instrument panel a touch larger along the way. And I think I have just about cracked it, while still retaining as much as possible of the 'feel' of the old system.

Fortunately I have a number of valves of similar vintage (RS8's as you can see were well vandalised) and I'm taking a leaf out of Sentinel's book by making the direction valve pre-selective, in other words, there will be a 4/2 pilot/pilot valve which actually controls air to the gearbox cylinders, and the manual valve 'up top' controls the pilots. But this valve will only have air to it when a button is pressed (there will be one button, and adjacent) and the standstill detector is branched off so if the loco is moving, air to the direction valve escapes to atmosphere. But air to the button is being tee'd off the clutch 'out' side, so effectively the gearbox can only be reversed when RS8 is stationary and clutch out. On the clutch 'in' side, a 'normal' timing system of capacity reservoir fed through a flow restrictor, and operating a 3/2 valve that interrupts the clutch air feed and vents off what's there is planned, but as an added twist, a shuttle valve brings an alternative feed from a roller-operated valve detecting the throttle. Thus throttle open = air fed to shuttle = unloader valve blocks clutch 'in' side, should effectively mean that the clutch cannot be engaged unless the engine is idling.

Meanwhile the chain for the handbrake linkage and the missing taper lock bush have arrived, and after numerous e-mails, I collected the bearings, seals and sundries for the two control shafts that run across the front bottom of the cab. On the brake shaft, there is also a counterbalance weight. I'm not entirely sure what it's for, unless, like a steam loco valve gear shaft, it's to offset the weight and stiction of the numerous linkages, but anyway I passed it to Andy H a week or so ago and he has sent me two pictures of it cleaned up, prior to painting, revealing it has been welded up from various bits of flame-cut slab!



Makes me wonder whether it was 'invented' in the commissioning phase as I've never seen a drawing for it. And finally the news came through that the two springs I'd taken for professional attention were ready. The old springs had been stripped, cleaned, and finally put back together with traditional hot buckling, and now look better than the two already on!


Which about brings me around to Saturday. Andrew was not available which meant that I had a day to myself. When Charlie was being craned on to the lorry to come home from Longcross, they accidentally caught one of the sandboxes, breaking the pipe and mountings, though fortunately not damaging the ejector. Fox had treated me very well so we decided we would deal with this at our leisure, but it really should have been attended to sooner. So, I dropped off the air feed pipe, removed the ejector from the bottom of the box to get the sand out, and then unbolted those bolts that still held anything. Currently it's inside waiting attention – I was for warming it up and straightening it, but Andrew, when he got to look at it, favours cutting off the bent parts and replacing with new material.


While the weather was still dry I decided to remove some more of the rotten timber that still adorns the RRA chassis – Andrew's plan is that when we re-bogie the PCV (planned for sometime soon) we lift this off its wheelsets and prep it for sand-blast, so cleaning off superfluous material is worth a few minutes. At the end of last week we had put the new pigeon hole units into place but had displaced a cupboard which Andrew wanted to reposition somewhere on the north wall. Given that I had squeezed my way past it repeatedly this week I decided that I would single-handedly see if I could at least get it somewhere near. So with brute force and a sack truck, and after moving various obstructions (clutter), it migrated over to the north wall by the matterson control panel. And as I was whistling to myself and enjoying my own company, who should walk in by Toby K sand Stephen M, who had been entertained by Andy H to a tour of a nearby old mine, and had dropped in to see me, or rather, I suspected, in the hope of getting a cup of tea.


 We didn't get down until nearly lunchtime on Sunday and my first task was to do a quick set-up and test a Lang control valve which will in due course become part of RS8, but Andrew's self-appointed task was to crack on with priming some of the bits Paul M sandblasted the other week. The pressure-pot spraying needed something mightier than the little hobby compressor which we have had a decade or more now, and the recently acquired industrial one proved to be well on top of the job. The loose cab doors and lift off's for Adolf were primed, together with the cab top and bottom and the casing grille.



Only the main casing section was left (for today) as it was too close to 1382 to be sprayed without risk of carry over. Along with Wickham wheels and trailer bracketry, he applied about 5 litres in the course of the afternoon and pronounced himself well satisfied, though we did start talking about a fume extractor! I spent some of my time in the container, going through stocks of valves and sorting out ones to fit the new control system for RS8. Hunting through years of acquisitions (there's stuff in there with YEC labels on going back to the 90s) I found a tank filler cap which gave me some ideas, so that too is in the van to introduce to RS8's fuel tanks and see if there's a marriage to be made.

So all in all a week of quiet progress. And what's due this week? Well, it's back to Tunstead tomorrow – the fabricator should be back with us and I'm hoping that Pete C has found us a portable MIG for the day so that one or two welding jobs on the loco can be carried through, but I also want to set him on cleaning off the old and manufacturing hinges for the new battery box lid. Then on Tuesday there's yet more parts for RS8 due in, including the new clutch cylinder which if the brackets get made tomorrow should be ready for it. So another fun-filled week. See you next time?


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