non-oiling of working saturated steam engines

[james mitchell]

I Note that there was a webinar on this subject recently, which I managed to miss. The attention was focused on the returning to steam of some of the engines at MSI, Manchester. Maybe i’m a bit late but thought its worth adding a few thoughts here.

First I should mention that I came to engineering conservation as an engineer, so had a head start in some respect. One of the projects that gained me ACR status was the Trencherfield engine conservation in Wigan. The learning curve on that project was dizzying!  However where I first learned about non-lubrication of saturated steam engines was on historic ships. I hasten to add, we are talking about  internal cylinder lubrication here, not external operating systems such as valve gear or mechanical packing.

The reason for the practice on ships is quite simple. Fresh boiler water in a marine environment is a precious commodity and carrying “top-up” water, while necessary, is an expensive luxury. that meant that condensate being returned to the boiler had to be as clean as possible to prevent carbon build up on boiler tubes, leading to  fuel wastage and ultimately hot spots and tube or shell failure.

Most of the steam ships in conservation today do not use “cylinder oil” in their engines for the above reasons and this is exacerbated by the fact that replacement boilers depend much on the science of metallurgy and treated water, thus allowing a lighter more efficient build.

While this practice was and is for reasons of fuel and plant economy there are good reasons why we should pick up on it today in a museum environment – yes, for the above reasons but also for sound environmental reasons.

Many preserved engines happen to be horizontally opposed… Mostly winding engines or mill engines. these pose another challenge as many marine engines are vertical or diagonal, thus reducing the dead-weight effect of heavy pistons working on their sides in their cylinders. Also preserved engines often work at lower speeds, loads and pressures.  (ah, I hear you say, surely that protects the conserved engine?) I would argue the opposite can be true.  Mill engines were designed to “fly.” Not a very scientific expression, but they were designed to run at relatively high speeds and at the highest pressures the (often) Lancashire boiler(s) could provide. This meant that the pistons ran, centred in the cylinders with their deadweight largely negated. I would therefore contend that “gentle” running, while having some benefits, is largely negated by the other stresses arising.

So surely non-oiling will only make things worse? Well not really. As the age of reciprocating steam gradually faded, the science of tribology was coming to the fore and an increasingly forensic approach was being applied. Many Victorian and Edwardian engines were designed to run on organic oils which were challenging to say the least… oil galleries and entry points often “waxed up” and the foundations of historic engines, still in their original locations,  will testify to this effect. Latterly, many engines were running on much less oil than their tenters thought they were.

Today we use hydrocarbon-based oils which are more efficient, when correctly selected, (although is not always the case.) However we lubricate like crazy both in the cylinders and operating gear. (museums should look at their annual lub oil bill!)  So the first step would be to use less of the right oil.

In cylinders, if you are still hooked on liberal oiling, choose a thinner cylinder oil and add the finest graphite flake so the solution will still flow (not through sightglass oilers) when the oil is long gone the graphite remains, and is one of the best lubricants there is.

Ok, we come back to saturated steam oiling on horizontal engines running at low pressures and low speeds… yes this is a challenge, so I would argue as a conservator that to protect the engine while demonstrating its unique operation carries a duty of care and a well-reasoned approach – complicated further by our commitment to environmental protection.

We know that steam engines run well on saturated steam so lets address the particular problems identified above. First select a trial engine using a set of criteria too extensive to list here. Open the engine up and “benchmark” measure the wear in the cylinder, piston and piston rings, piston rod and rod packing. replace the “heritage” items such as piston rings and packing, with modern high temp plastics while setting aside or displaying the heritage items for long term preservation. Where necessary, “centre” the cylinder using the same material, thus protecting the liner, piston and packing box. Run the engine for a period agreed with the museum and then open up and measure again, observing wear both on the engine and introduced materials.  The decide on what you do next with this and your other engines.

Cylinder oiling can stop. packing and valve oiling carry-over reduce to a level that a plant skimming and filtering system can easily cope with

There are other measures to be taken in parallel with the above but you have the gist of it. I would contend that this is best conservation practice in every sense, going forward.

James Mitchell ACR FIES

 

[Alison]

Hi James,
Thanks for contributing this to the discussion. I am currently collating the material from the webinar as transcripts and a video to put on the Big Stuff website. Are you happy for me to add your message as a postscript? In particular I think your description of a suitable wear evaluation process would be very helpful for people.

Cheers – Alison

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