Title

While the main focus of the Strathspey Railway is running steam trains for the paying public, a small but dedicated group of volunteers has been restoring other items of heritage interest in spare moments between working on the loco fleet and improving locoshed infrastructure and facilities.

The current project is a Ruston Hornsby 48DS diesel shunter of 1948 which worked at Longmorn distillery until 1980 (even though Dr Beeching had closed the adjacent main line in 1967). Because it was presented to the Strathspey Railway repainted with advertisements for Queen Anne blended scotch whisky, it is known to most people as “Queen Anne”.

To find out more about our aims, follow this link or click the [About] button above.

This Blog was started over 5 years after the project began, so most of the initial blog entries are retrospective.

Friday, 16 June 2017

Injectors

The Achilles Heels of earlier Ruston engines are the injectors.  These were of Ruston’s own design and made in-house.  Although they worked perfectly well, they were difficult to service and because they were only used on Ruston engines, there are now very few spare parts left.  Later Ruston engines used CAV injectors, as did most small and medium-sized British-made diesel engines, and hence replacement CAV injector parts are more readily available.

The Ruston Mark 37 Injector

A Ruston Mark 37 Injector from a VPH Engine
The picture shows the components of a Mark 37 Injector :-
A    Plug (overflow pipe connects here)
B    Sealing washer
C    Needle Valve Stop
D    Injector Spring
E    Spring Washer
F    Spring Housing
G    Nozzle Assembly
H    Injector Body with inlet filter
 
The injector nozzle is the most stressed part as it is in direct contact with the hot combustion gases.  It is also very critical as it must produce a spray of very fine droplets of diesel to obtain correct combustion without excessive smoke.  It contains very small holes, which can become blocked, is subject to erosion, and the needle valve and seat become pitted leading to dribbling and poor combustion.  The nozzles are designed to be serviced at intervals and replaced when necessary whereas the rest of the injector will normally last the life of the engine.

The earliest Mark 37’s had a nozzle that was separate to the needle valve and guide and was difficult to line up correctly.  Subsequent injectors, including those on Queen Anne, had a combined nozzle, needle valve and guide which is a much more satisfactory arrangement.  The nozzles are machined to very high tolerances and must be kept scrupulously clean.

The injector pressure is important, and for the Mark 37 should be 3000 psi.  Other makes of injector have a screw device to vary the pressure on the injector spring, but with Mark 37s shims have to be placed alongside the spring washer (E), and this involves repeated assembling, testing and dismantling until the correct pressure is reached.
The Water-damaged Nozzle

The picture shows a nozzle that was badly pitted due to water entering the cylinders when the loco was abandoned.  It is obviously a write-off.  Unfortunately there seems to be no replacement nozzles to be found anywhere, in spite of contacting various specialist companies and Ruston experts.

The Wrong Nozzles

When the injectors were dismantled, it was found that the wrong nozzles had been fitted at some time in the past, presumably at Longmorn.  There was one of the correct type (VRH) and three for a VPH engine, which has double the cylinder volume.  The VRH nozzles have 3 x 13 thou holes and the VPH nozzles have 4 x 16 thou holes – quite a difference!!!
You can see the wording FVPH on the left and FVRH on the right.  Also showing the needle valve.

The engine obviously ran with VPH nozzles, and as VRH nozzles are unobtainable it was decided to use VPH nozzles in all injectors.  This meant replacing the VRH nozzle and badly pitted VPH nozzle.  Of course, VPH nozzles are unobtainable too, so it was decided to “borrow” nozzles (also in poor condition) from the out-of-use Ruston 0-4-0 DM shunter, which has a 6VPH engine.

Reconditioning

Two tools were made to aid in dismantling the injectors.  A simple removal tool screws into the Needle Valve Stop (C) and pulls it and the washer (B) out.
Simple Dismantling Tool

The orientation of the injector sprays is important, and an inscribed line on the nozzle must line up with a similar line on the injector body.  A special tool was made to allow all the injector internals to be lined up before sliding the injector body over.
The Assembly Jig

Injector Internals Mounted on the Assembly Jig

The injectors were reconditioned by Rayner Diesels in Newbury.  While they normally service modern diesel fuel injection equipment, they have many years expertise and still have the equipment and knowledge to service older injectors.  For injectors in such a poor state, renewal of the nozzles would be the normal solution, but in the absence of spare parts the nozzles had to be brought back to life.  The needles were seized in the nozzles and needed to be warmed up gently to soften the congealed diesel oil.  The valve seats were badly pitted and needed carefully lapping in with very fine grinding paste.  Most of the nozzle holes were blocked up.

The sealing washer (B) is a special shape as it needs to seal both the needle valve stop (C) and the injector body (H) against the full injection pressure.  These washers can only be used a limited number of times, so some new ones were machined out of copper bar.  Rayners were short of one good washer, so one of the injectors suffers from back-leakage until we have made and fitted a new one.  This should cure the white smoke which is currently being generated by No. 1 cylinder.


If anyone knows of a source of Ruston Injector Nozzles, please let us know.

No comments:

Post a comment