Turn 112 - Firing the 7F

 Well, I've not used the torch yet (apart from in the firebox) but the sun is rising as I drive to Weybourne now, as we near the end of the summer holidays and start to roster for the yellow Autumn service; the volunteer newsletter, Poppylines, is talking about plans for the Santa's and the Norfolk Lights Express.

Today is a new challenge - a firing turn on the old bogey, the 7F upon which I have occasionally come to a sticky end. Regular readers will know what I'm talking about!

The old 7F has a drop grate, and the previous crew had left a very thin fire, so it didn't take me long to get rid of the remaining ash. I'd scooped a barrow full of ash out of the smokebox before I started on the fire, and I'd got myself a bucket of rags and paraffin to try to avoid climbing on and off the loco more often than I had to.

The tender had mostly dust and ovoids, so with Driver Paul's words ringing in my ears I shovelled a few scoops under the arch, followed by a lot of wood to get it hot really quickly. in this way, you can light the fire without making much smoke.

During prep, I have to admit that I had forgotten to check the injector isolation valves fitted to this loco (and the B12) - you must make sure these are fully open and wound back to seat the valve at the 'open' end of the travel. When I spotted them, they were already open from the previous day.

Prep went very smoothly that day and Driver Henry and I managed to clean the boiler barrel, smokebox, cab, running boards and tender between us by the time we went off shed.

The day was pretty uneventful really - I fired the first three trips quite successfully, though the first trip up to Weybourne was a bit cold, as it often is - I think we were around 150 psi when we arrived at Weybourne, but with some coal and a bit of blower it was soon up to pressure - I had plenty of water though. You need a decently thick horseshoe in the back of the firebox. 

I drove the fourth trip with Driver Henry on the shovel, and we had a spirited run on the way up which brought a smile to a few faces when we stopped at Holt, and a cautionary look from Driver Henry when he thought I shouldn't give it any more - he was still grinning though!

The 7F is fitted with the Midland pattern brake valve, which operates both the train brake and the loco brake: 

It's described in the LMS 'Black Book' or "Questions for Enginemen &c." to give it it's proper title, and it shows this nice cutaway diagram below.

It's a bit unusual in that the operation of the steam brake, even light engine, needs the ejector to create vacuum in the train pipe 1. The operation of the vacuum brake is fairly obvious from all the holes in lever 7 - operate the lever to 'on' and air is admitted to the train pipe. Now, the steam to the loco brake cylinders controlled by the steam brake valve 4 - it moves to the right to admit steam to operate the brake to on. 

You'll see that the steam brake valve 4 is operated by the lever 5. Lever 5 is operated 'off', to the left, by a piston 3 - in normal running this has vacuum at 2, and ambient air pressure at 8 (see the holes drilled in the 'piston rod'). When the vacuum brake lever is operated 'on', in addition to allowing air into the train pipe (which lessens the force on piston 3, holding the steam brake off) the ramp part of the brake lever pushes the steam brake lever 5 to the right, opening the steam brake valve and applying the steam brake - the steam brake will come off again as the lever is moved to off, increasing vacuum and the force on piston 3.

Now, if the loco is standing with the tender brake on, steam can be saved by switching the ejector off. If this happens, lever 5 can move to the right since it is not restrained by piston 3, which in the absence of vacuum is free to move to the right - which would allow the steam brake to come on, wasting steam. To prevent this, there is a hook at 6 which holds the steam brake off in the event of there being no vacuum.

This hook is specially shaped to hold the steam brake on when you want the vacuum off, but don't want to use the handbrake - perhaps at a signal, when the guard is testing his brake, or when you are about to move off. It's got a notch in the top of the hook which holds the lever 5 in the 'steam brake on' position, as shown in the picture above, and you can easily flick the lever out of this notch to let the brake off when you are pulling away.

This braking system is quite different to the other locos, which all have separate vacuum brake and steam brake levers, and takes a bit of getting used to. My first stop at Weybourne was a bit more sudden than I would have liked, but the stop at Holt was as smooth as you like and in the right place - I overdid it on run around though and managed to stop the loco halfway into the headshunt, so that I had to get it moving again. The rest of the trip was fine, and I'd got used to it by the time we got back down to Sheringham.

We had a bit of shunting to do before home time - our train needed to be moved to the loop, so that we could pull the dining train out for the fish and chip service. Driver Henry handled that, as my experience is really not up to that kind of precision driving!

Disposal was pretty straightforward - there was a bit of clinker at the back, probably caused by all the ovoids we'd used. 

I finished the day by clearing out the pit and left with a lot more confidence in this old girl than I arrived with - I had let it blow off once, had no water level problems and certainly hadn't stopped in section!