Work continues above the windscreens and the scabby metal has now been cut away and the metal below cleaned up to see what can remain and what needs to be removed, right to the base of the small section of angled steel above the centre windscreen, the screen itself covered to protect it from metal fragments during the cutting. The dome is pretty beaten up from years of pigeon and bird strikes but also previous repairs, you are looking at the original surface of the dome as evidenced by the br green paint towards the centre, the textured surface is from the glass cloth scot rail applied which has now been removed, the dome will need considerable sanding and and fibreglass filler before the metal work can be tended to. The angled clean steel is part of the base of the dome steel supports which is in fair condition.

 

 

the cut continues above the drivers windscreen, you can just about see the weld lines for the original (pre HGO) windscreen the two large holes are for the wiper control arms, these will be filled with fibreglass cloth and re-drilled, the drivers windscreen will be removed to inspect the condition of the seal edges, and any wasted metal replaced, as water that can get into the seal will damage the windscreen and cause delamination.

 

 

On the drivers corner pillar after the paint and relatively thin layer of filler has been removed, we see as expected significant corrosion and we will need to establish the cause...if we just put fresh metal in the corrosion will re-occur, also note the bulge above the side window...this too, is abnormal and indicates issues behind the steel in this area....It would appear this is an old repair from impact damage.

 

 

with that corner removed considerable corrosion is present behind it.....its more than likely this has been caused by a leak in the horn box area likely due to a poorly sealing lid and the water is finding its way down the front corners of the dome....and then running down the crash pillars previous repair attempts to the dome can be seen with the metal removed you can now also see the extent of the bulge. part of the dome will be cut away down the side to determine the condition of the roof supports which also hold 3 very heavy air tanks inside the cab, its possible that they have corroded weakened and started to sag, so if that is the case they will be jacked up and repaired. The dome requires considerable attention also.

 

 

A rough paper template has been made to start cutting the new steel.

 

 

No1 end second-mans door has had its hinge recess strip ( a posh name for a 6mm thick bit of steel....well it was 6mm) removed, there was considerable signs that all wasn't well in this area.....and after removing the door....(which will go back to Scotland to live on another loco) and the strip as evidenced by the paint outline....you can see considerable issues...after a good attack from the needle gun....

 

 

 

The corrosion goes all the way to the base...

 

 

And up to the top...….this is why you make sure not only does the door fit properly.....but its also sealed....if you don't, this happens this isn't structural steel its just a skin, directly behind this is the grab handle recess, this will be replaced with 6mm plate to give the doors something to bolt into

 

 

Work continues in No2 cab refit Drivers side heater conduit painted the regulation orange and the heater permanently wired up.

 

 

The second-mans side is a slightly more complicated affair with the heater light switch and DSD holdover switch (allows the second-man to operate the DSD if the driver leaves his seat) The switch box hasn't been fitted, the wiring (about 7 wires in all) has been mostly threaded there are some crimps that need renewing, the heater has been wired up, the light switch box has been fitted it just needs some modification to the lower conduit to accommodate the DSD holdover switch box the white panel at the side of the desk is brand new and the wooden window surround is being renewed where required and refitted.

 

 

On the drivers side the Fv4 valve has been removed to renew the crimps to the wires going to the valve (more on that later) and to put more screws in to the drivers side panel to stop it rattling, at this point the opportunity was taken to renew the O rings that seal the valve body to the base plate, the thick pipe is actually the locomotives vacuum brake pipe...

 

 

This is the Fv4 valve itself (otherwise known as the train brake valve) its the largest valve in the cab of an D+M (davies and metcalfe) equipped locomotive for which 20s 25s 26s 45s and 47s were so equipped (56s have a similar valve but its looks it only shares with this valve) this, although it looks a little beaten up is a recently professionally overhauled valve. There are types of valve (non banded...yellow banded and green banded) as you can see this is a yellow banded one.....whats the difference?

 

Non banded Overcharges and speeds up the vacuum exhauster the brake pipe when when release is selected

Yellow banded speeds up the exhauster but does NOT overcharge the brake pipe when release is selected

Green banded (quite rare) has no exhauster speedup facility

 

The reason 26s have a yellow banded Fv4 is because they have a brake overcharge plunger in the form of a big brass plunger on the drivers desk. The brake overcharge facility is used when you have a long air braked formation and it ensures that the brakes at the rear are released. Overcharge does not affect vacuum operation.

 

The two terminals are shorted when then release position is selected, and this is used to place a resistor in series with the vacuum exhauster motor field, this as a result weakens the field speeding up the motor and creating vacuum faster, which...saves your embarrassment when you have bled off too much vacuum during braking and you don't want to stop....or...it allows a quicker brake release pulling away from a station...

 

a side affect on a non banded Fv4 is you will also overcharge the brake pipe but more on this later....

 

 

Another view of the vacuum brake pipe, this bolts to the Fv4 and is operated by that little nipple....

 

 

the Fv4 valve now installed and bolted down without the vacuum brake pipe attached, the handle is in the full service position note the notches on the ring and score mark, these give driver a tactile feel in dark conditions about the position of the handle at the right of the white handle there is a small pointed plunger which drops into these notches and allows the driver to feel where the handle is in the dark. The notches correspond to the the following...

 

Running (basically brakes released)

initial - brakes rubbing...with a little pressure used to control your speed descending an incline rather than actual braking)

from here the brake is stepless to full service

full service (maximum brake pressure but applied in a controlled manner)

Emergency considerable force is required to put the valve into this position (you cant do it accidently) you don't get any more braking than full service you just get it a lot quicker.

shutdown used to seal the vacuum pipe in order to change cabs.

 

NO DIESEL and that includes VAC ONLY diesels (apart from the twins 10000 and 10001) has a vacuum brake...what I hear you all cry...yes you heard me...a diesel does not have a vacuum brake, the only physical influence the driver has is on the emergency portion of the vacuum brake, a conventional diesel locomotive does not have a vacuum cylinder. In simple terms The Fv4 valve simply reduces the ATP (automatic train pipe) which the locomotives air vac relay valve senses and operates a diaphragm to allow air into the vacuum brake pipe, this causes the air to be emitted to the rear of the vacuum brake cylinders on the coaches or wagons on operates them which through linkage operates the brakes on the vehicle....on the locomotive the triple valve compares the value of the vac chamber (a small tank that always has 21" of vacuum as a reference) to the value of the vacuum pipe and applies the locomotive air brakes in proportion.  A locomotive with an empty chamber will not apply its locomotive brakes in proportion. 

 

This also means that the train (with a higher brake force) will do most of the braking effort...but also means that the carriages (because they are braking more and therefore the locomotive always releases its brakes first will not slam into the back of the loco allowing for smoother braking.

 

 

When emergency selected the valve mechanically forces this little arm out....which operates the nipple.

 

 

And here is the vacuum pipe attached with its trapdoor valve in the closed position which seals the vacuum pipe and relies on several valves on the brake frame to ensure that the vacuum pipe operation is within the correct pressures according to demand from the driver, this why the train brake is also sometimes known as the automatic brake, and its governed entirely by the automatic train pipe, which is air, and governs the operation of the train brake.

 

 

here we have the brake valve in emergency the trapdoor valve has been opened by the arm actuating the little nipple on the trapdoor valve which opens it and instantly vents the vacuum pipe....which drops the vacuum to zero causing the brakes to fully apply on the train.....the locomotive compares the zero vacuum pipe to the chamber and as a result now knows to apply its locomotive brakes fully...ensuring maximum braking effort is available to the locomotive and the train.

 

The Fv4 is probably the most complex valve on the locomotive, its extremely intolerant of wear and as result internally contains a lot of hardened corrosion resistant material, they are also one of the most expensive valves to overhaul (which has to be done by a specialist contractor) and cost close to £1k to overhaul, and that's just one of about 40 different valves on a dual braked locomotive. They also have lot of rubber seats and diaphragms which degrade over time.

 

The operation of the brakes is tested and carefully compared to the BR specification every year, but in addition the driver has to complete and sign a brake test every time the locomotive is used, which consists of a test to ensure that the brakes react as expected before the locomotive enter service every time.

 

 

 

finally with the drivers screen removed considerable repairs have been made to the dome ready for welding.