Saturday, 9 April 2016

The learning curve continues - Alfred's lubricators

Last Sunday while running 'Alfred' at Urmston we noticed a problem with his cylinder lubricators.

Steam locomotives have to supply oil (heavy grade thick steam oil) to their cylinders to provide lubrication for the piston in the bore. These lubricators can either be mechanical (effectively a pump driven off the locomotive's motion) or 'displacement'. 'Alfred' has displacement lubricators with the added refinement of sight glasses. This combination is sometimes known as a 'hydrostatic' lubricator. But how do they work?

Under 'Alfred's footplate is a brass vessel we keep topped up with steam oil. A fine capillary copper tube supplies boiler pressure steam via a condenser (turning it to water) to the vessel. The water pressurises the vessel, and the oil floats on the water. A second pipe allows the pressurised steam oil to leave the vessel and feed two glycerine-filled sight glasses mounted on the inside front wall of the loco cab. The sight glasses have an adjuster each to regulate the incoming oil to one drop every several seconds, which one should be able to see travelling through the clear glycerine from the bottom of the glass to the top. From the sight glasses, the oil is fed by two copper pipes, one to each of the two cylinders.

What we have noticed recently is the sight glasses have become discoloured with oil, especially the left hand one. This may be because until we did some extensive research we didn't really understand how these lubricators work, that the sight glasses contain glycerine, or that there is a definite procedure to follow for the lubricators when lighting up or disposing the locomotive.

We'll be following that procedure in future!

So I decided to remove the sight glass assembly, clean it thoroughly, and refill the glasses with fresh glycerine.

The sight glasses, discoloured with oil, can be seen next to the boiler pressure gauge on 'Alfred's cab front wall

The footplate with the sight glass assembly and the pressure gauge removed. I removed the latter to allow enough room to gain access to the gland nuts securing the oil feed pipes to the back of the sight glass assembly. 

The other side of the cab wall, showing the two oil feed pipes to the cylinders and the empty holes where the connections to the externally-mounted elbow piece for the oil pipes pass through, and for the fixing screws for the removed components 

The condenser coil for the steam supply from the boiler to the steam-oil vessel. Air blowing in through the open window will help with the condensation process. 

On the right is the now cleaned sight glass assembly, while to the left is the 90 degree elbow piece which sits externally on the front face of the cab and connects each sight glass to its cylinder lubrication pipe. The threaded caps have been removed from the top of each sight glass to aid cleaning and I'll use a syringe to fill the sight glasses with glycerine before replacing them.

Removing the footplate floor reveals the steam-oil vessel (bottom right) with its hex-headed filler plug on top   

 Job done! Everything back in place, with fresh clean glycerine in the sight glasses.

We'll find out if the lubricators now work correctly tomorrow at Urmston. Once steam pressure is up I'll open the steam feed to the oil vessel, and adjust the adjustors on each gauge glass for one drop of oil every 30 seconds to pass through the glycerine, bottom to top.

Fingers crossed!


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