Tuesday, 7 April 2015

Vacuum Braking (8) Implementation (2)

In Implementation (1), I showed some of the vacuum braking system pipework. Below is the fuller picture including the safety valves, manifold and feed to the vacuum system.

From the safety valve manifold (with the flange), there is an isolating valve, a blue pressure reducing valve, a 'cross' for feeding the ejector (jet pump), a condensate drain and pressure gauge and then the ejector itself and its up-standing, tall exhaust pipe.

Off to the right of the ejector is a Gun Metal Lift Check Valve, a 'T' to the train pipe, a 'T' for a vacuum gauge, a 'T' with the vacuum relief valve in place and finally the brake operating ball valve with a Sintered Bronze Pneumatic Air Muffler (silencer).
A bit more of the beginning!
The train pipe is a challenge in itself for reasons which will become apparent later.

Originally, I'd conceived the train pipe to be made from 2" nominal inside diameter pipe as used on 'big' locos. However, a discussion with Michael Patterson, who is restoring Sentinel 9366 at Quainton Road, made me appreciate that we will not be attempting to evacuate rapidly a train load of 14 Mk1 carriages. Instead we might have 2-4 carriages which will be a much less demanding task. Add to this that the ejector itself only has a 1" diameter suction pipe and it calls into question the need for 2" pipe. Add also that I have ready access to pipe threading tools that can handle up to 1.25" pipe and the case for 2" get even slimmer still.

I thus decided to use 1.25" galvanised pipe and malleable iron fittings for the vacuum system with adapters to the 2" standard fittings on other vehicles.

The basis for one such adapter is shown below. The classic steam loco's 'Swan Neck' is constructed as below. The 1.25" pipe is adapted to 1.5" fittings which can be turned down to make the correct diameter to fit the rubberised vacuum hose. A short length of support pipe may be needed to keep the pipe from slipping off (unlikely when a vacuum is present but safe if it did happen since it would break the train pipe and put the brakes on).
Swan Neck
On 7109, the rear one looks like this after turning down the 1.5" 45 degree fitting.
Rear Vacuum Pipe and Swan Neck
The vacuum pipe routing is not going to be easy but is made less challenging using the smaller pipe diameter. One possibility was to route the pipe under the RHS running board. However, this space also has to accommodate the sanding box operating mechanism, the extent of which is currently unknown. To wait for the sand boxes to be sorted would bring this activity to a halt so I decided to do it the hard way!

This is the plan:
The rear pipe has to tuck under the buffer beam and across it.
Inside the rear buffer beam
Then it will pass in front of the handbrake mechanism and round the large bracket...
Hand-brake mechanism
...and along the inside of the off-side loco frame.
Inside the frame below the footplate looking rearwards
The curved pipe in the above photo has been removed.

The pipe then has to come forward to where it will 'T' off upwards to the vacuum ejector suction port and brake operating lever.
Forwards through a restricted space
Then things gets tortuous. The pipe has to cross from the right to the left between the lagged exhaust pipes and the water tank...
Between the upward exhaust pipes and the rear of the water tank on the left.
... and along underneath the water tank to the left of the three insulated pipes.
Space to the left of the three insulated pipes
Finally it will cross beneath the engines and connect to the front vacuum pipe and its Swan Neck.

The first few steps are shown below.
First it tucks under the buffer beam via a right angle union connection to allow the Swan Neck to be aligned rearwards.
Tucking under the buffer beam
Then it crosses to the right under the footplate...
Under the footplate
...and to the front of the handbrake screw mechanism...
Avoiding the handbrake
...and round the bend via another right angled union to enable the next section to be attached from the front.
Right angled union
The pipe is held to the footplate above by Aluminium Stauff clamps which grip the pipe tightly and provide a strong mounting. M6 Allen-headed bolts of 70mm length are used to attach the clamps to a threaded hole. Flat and spring washers are also needed to spread the load and prevent the bolt shaking loose respectively.

The pipe advances forwards through he gap at the top of a supporting bracket.
Handy gap for a pipe
It needs a dog-leg to avoid the rear RHS wheel.
Section of plank supporting the pipe
Now it gets to the tortuous part but that's for another article as I haven't got there yet!

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