Weekend Rails

what we do for our kids

Of  sensors and skips

29th March 2015

Obviously one of my regular readers decided to follow up on my plug for Fascinating Aida as he wrote to me during the week to say that if I ever bought a Smart car he would never be able to look me in the face again. While it is a proud boast of mine that I have never owned a car with a “boot” (the nearest I got was buying my former company car – a Ford Escort hatchback – from Thomas Hills in the 80s) I think that would be going too far. I did once tell someone that I thought my next car would be electric – that was about three or four vehicles back – but the technology hasn't quite made it. Well, not in my price range.

Incidentally, Fascinating Aida, were, as ever, hilarious on Friday night. Steph and I have now seen the “Charm Offensive” four times, I think, in Sheffield, Chesterfield, Bradford and Darlington, but the tour finished tonight in Belfast and the new show won't launch until August 2016 so we shall have to live on the memories until then.

I predicted last week that the man delivering the skip from Mr Booth would not think to ring me until he'd arrived and found the gate locked (and in a more cynical moment wondered whether he'd think “Briddon” and head to Rowsley without checking) and mid-way through the morning had a call to the effect he was sat outside the station. I leapt into Steph's car (a Micra, not a Smart) and hurried down, and there he was, and within ten minutes he was unloaded and on his way, apologising for having read – and then largely forgotten -  his instructions. No matter, it will help keep the site tidy as we prepare to bring our materials down from Rowsley.

What with month end and year end fast approaching it has been a week when work on Andrew's locos has been on a bit of a low. Granted, I did order up the pulley and bush for the 03's vac exhauster drive along with some other bits, and they were due Thursday. But half-way through Thursday a phone call revealed that they were only leaving the supplier that day, so expect them Friday. As it was I had a call Friday morning to say that some profiles were ready for collection, so took with me the spare fuel pump for a Rolls C6N which will be overhauled ready to go into Charlie shortly.

Anyway, while I was away Steph and our grandson listened out for the carrier. I was back after lunch and by quarter-past four came to the conclusion that unless it was UPS (who come past on their return to Afreton) it wasn't coming today. The supplier was still open and gladly gave me a tracking number – for TNT. A sick feeling in the pit of my stomach ensued and yes, the TNT website revealed it had been returned to Nottingham branch “for verification of the address”. I phoned TNT and expressed my disappointment.. They promised to put it out for re-delivery with my simple instructions of how to find the Briddon Country Pile plus my contact number (though TNT won't provide their vehicles with mobiles, they say, so unless the driver uses his own  - which the last one did -  this is no use to them). On Saturday morning I checked again and found it down for delivery on Monday. I wrote a strongly worded e-mail to my supplier to demand a refund from TNT.

So on Saturday, after the rain had stopped, Andrew and I headed down to Darley and had a quiet afternoon as the railway was not operating. While I got on with “some other jobs”, Andrew disappeared into the container and started assembling some new racking he'd bought during the week. It was surprising how some of our “secure” racking had crumpled when the container had been slewed,  pushed down the line and slewed again. This time he's adding stiffeners across the top to brace the bays on opposite sides, and we can hang some strip-lights to them as well.

Today Steph, Andrew and grandson were socialising, leaving me to get on with some boring stuff like invoicing, etc, but I did get around to trialling the LED card in the prototype codelight box for 03 901. And here it is.  


If you look very closely you can actually see the pin-pricks of each LED refracted through the bulls-eye lens, but it is a vast improvement than the disco-ball effect of the original, which card you can see propped up at the side. The card mounts to a "cartridge" that slides in to the body from underneath and the changeover switch is located there.  I also made time to test out a revised plan for the direction sensors on the 03. And with that, it is time for a little tale of yesteryear.

Back in my days at Hills, we needed to know whether the locomotive was set to move forwards or backwards, and although this might be assumed from the position of the direction control, we were conscientious enough to desire to know whether the box was in fact fully engaged, not merely  “ought to be”.  

In  fact, it probably gores back to the Sentinel control system. Back when Sentinel designed the pneumatics, they talked to steam loco drivers who seemed to think that the ability to put the reverser into the opposite direction, and thus move off again as soon as the loco came to rest, was an essential feature of a shunter.  You could do this with a  Sentinel steamer, but the new diesels would have this SCG RF11 gearbox, and reversing that required things to be stationary. So they hit upon the idea of making the system “pre-selective” which sounds grand but essentially means that once you've moved off, the forward/reverse control valve is de-pressured and you can set it anywhere you like. It was therefore a 50/50 chance whether the control matched up with the selected direction in the 'box, and Sentinel fitted limit switches operating through the ends of the gearbox  air cylinder covers to detect which way it was actually set, and illuminate panel lights accordingly. Yet somehow drivers would cope when the bulbs in them failed.

Hills never liked the limit switches, they were prone to getting bunged up, and as there was no gland around the operating shaft, it actually became an air leak, getting worse as the loco got older. The RF11 had a manual handle on the back, provided to enable you to put it into a mid position for towing. It worked off the selector shaft via a brass block, lever and shaft to the outside. So Hills put much bigger limit switches or air valves either side of the handle to determine which way it was set.

But the RF11 had one weakness which gave us problems.  Occasionally, the lever would snap off the shaft, allowing it and the brass block to fall down inside the box.  If the loco then went in one direction, these not-insignificant lumps fell to the bottom – you drained off the oil, removed a cover and felt around inside to get them out. You knew it had happened because the direction lights stopped working, or if it was all pneumatic, the whole loco wouldn't change direction any more. If however the loco moved the other way, the lever and brass block became trapped on the final gear stage: it had nowhere to go and usually it took out two or three gear teeth. Not enough to stop the loco – the RF11 was nothing if not rugged – but enough to make a noticable clunk every rotation of the wheels.

By the 80s you'd think we'd know all this, but we were still capable of dropping fresh clangers. In this case a couple of radio control conversions of Sentinels for BSC Ravenscraig and the first two “Valiants” for Blue Circle had a new system, whereby a 1” thick profile shaped like a  spanner was bolted directly to the RF11 manual handle, and a single limit switch was  toggled by its jaws. I got very much involved with the Blue Circle pair, and was aghast to discover that the direction detection system had failed on one – indeed, I had a large segment of one its final drive gear teeth on my desk for months.

I realised on investigation that we had created our own downfall. The original RF11 manual handle was in cast-iron, but SCG had changed it to aluminium, I deduced, to reduce the inertia as the air cylinders banged the lever and brass block to and fro. Our spanner-shaped profile had put back all that mass, and more, and the weld had failed as a result.

Somehow this was an opportunity for one Johnny Otter, Hills' Electrical Design engineer, to put forward a proposal to use what were then relatively new “perception head” sensors. (I say “new” - probably some electronics whizz out there will assure me that they'd been out for years, but, given the innate conservatism of the railway industry,  “new” ideas and components needed to have been proven for 15-20 years before we'd adopt them). These are 3-wire devices, whose electronics are set into a threaded tube. The wires come out one end, and a suitable piece of ferrous, coming close to the other end, switches the output on. Put one into each cylinder cover, rather like Sentinel's original limit switches, but forming a reasonably air-tight seal, and you can detect the piston at each end of the travel.

We installed the first conversion on a Saturday afternoon and it worked a treat, becoming Hills standard thereafter, with “upgrades” taking place at Ravenscraig too (and yes, one of theirs had snapped), and I have used it subsequently on all manner of locos, though usually smaller sensors than those we first fitted to the Valiant. They have one limitation though, and that is the current they can switch. Try to put too much load on them, and they shut down as if it is a short circuit. On the 03 I had made up a card using solid-state relays, but located this in a box where the sensors would join to the multi-core cable.

This was my mistake, as when the lads were ripping up the floorboards last year they managed to clobber the enclosure. For that matter, relays have come on a lot in recent years and whereas my old standard was the 8 or 11 pin plug-in relays from Hills days, I have in stock now  relays that I use on my dynamo regulators that are rated at 10amps but barely bigger than a sugar cube and operate on a current of milliamps.  I set one up today and sure enough, it operates happily off the sensors, and  so I will put together a new little board to go up in the dry of the instrument panel where it can finally light up the forward and reverse LEDs. And then I can turn my attention to a working speedo for it.


More in this category: « Of LEDs, tachos and squiggly bits

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