Oil in Boilers

Can anyone explain the effects of when oil or grease gets into a loco boiler and the reasons why it happens?

 

My experience of oil in loco boilers is that they tend to prime badly. New boilers are especially prone to this as there is all the oil from the manufacturing process, such as ithat used in drilling and tapping the stay holes. A couple of steamings and water changes seems to get rid of it, though.

 

Correct, the contamination causes them to foam and lift the water in that manor, rather than from having over filled the boiler

 

I'm sure I read somewhere in one of the fireman memoirs (might have been Harold Gasson's firing days series), that old school drivers would drop a lump of grease or pour steam oil into the water tanks to try and generally free up the engine and make the regulator easier to pull - particularly on shunting turns where the regulator is opening and shutting all the time.

I've not yet tried this myself 'cos of my perceived risk of priming...

 

Yes I remeber reading it too, but can't remember where!

I think you're right; this was on shunting engines to free up the regulator, which would be in constant use while shunting, until it bedded in. I doubt that it was done on a main line loco: the regulator wouldn't be used as much and priming would be much more of a problem than in the short bursts of having steam on in the yard.

Terry Essery also did an article for Steam World entitled, I think, 'Frothy'. The gist is that a gallon or so of degreaser was dropped accidentally into a Black Five's tank with spectacular results when it next went out!

 

On GWR locos, the hydrostatic lubricator does have a sight feed for the regulator. This runs at a much slower rate than the ones for the cylinders.
"Two drops a fortnight," as one of our inspectors put it.

 

The oil breaks down the surface tension of the water making it boil furiously. When the regulator is opened a localised low pressure is created around the end of the main steam pipe. This low pressure makes the water boil even more energetically, making it much more likely to be carried over to the valve chests and cylinders than if no oil was present.

 

I have heard of another technique used which would need balls to use...

Shut the gauge glasses off (assuming they DO seal) and open the drain... most gauge glass fittings have a threaded plug for rodding the internal passages. Apparently, a method used to be to take this plug out and dribble a small amount of steam oil in then replace the plug.

As soon as you re-open the gauge glass cock, you open the regulator and this should suck the oil straight off the surface and upto the regulator head without contaminating the water... I've never tried it, but it's supposed to work!!!!!

I'd want to be pretty damn sure the shut off cocks worked though!!!!

 

I did see a driver do something similar a many years ago to cure a stiff regulator. What he actually did was shut off and drain the gauge glass, take off the cap nut and remove the valve, then filled the gaage glass with oil and replaced the valve and cap nut. The idea was that by only opening the steam cock the oil stayed in the steam space and found it's way to the regulator without causing priming. I think it worked but I wouldn't think maintenence staff would be very happy if they knew he'd done it. If oil is carried around in the steam it would obviously find it's way into other components such as injectors and brake ejectors as well which may not be such a good idea.

 

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The presence of oil in the boiler can be to the detriment of the life of the engine. On GW engines with a hydrostatic lubricator, if the boiler pressure drops below that of the lubricator then a trace of oil can pass back. This can lead to the priming and foaming etc. This can just be annoying if handled well but it can cause big overheating in the firebox, causing a serious pain in the cheque book.

 

The pressure in the lubricator is always slightly more than the boiler due to the condensate head produced by the Chinamans hat. It is, however, only about 2 psi.

 

But as boiler pressure drops off it can back feed. You look at the valve on GWR lubricator coils, there's often a trace of oil there.

 

So, if some of what has been said is true how come there are numerous patents from pretty serious companies, technical papers and articles by railwaymen at the sharp end detailing the use of various forms of mineral and non-mineral oils as antifoams? Prior to the 1940s oild based antifoams were about the only ones available.

 

An extract from BS2486 water treatment in boilers I think this explains the problems of oil in your boiler water.
Regards
Keith

6.2 Condensate contamination by oil
Every effort should be made to avoid contamination of
feed water by oil. Condensates containing oils should
be rejected for the following reasons:
a) vegetable oils introduced into alkaline boiler
water are usually converted into soaps which can
rapidly form a stable foam on the surface of the
boiler water and can lead to severe contamination of
the steam. Where this risk exists, continuous
addition of an anti-foam is prudent even when
contamination is not apparent;
b) mineral oil introduced into the boiler can form
non-wettable films on heat-transfer surfaces and
interfere with the detachment of steam bubbles so
that the surfaces are inadequately cooled by the
boiler water. As a consequence severe corrosion or
overheating failure of such surfaces can occur. This
may be a particular problem when steam is used to
drive prime movers. Lubricating oil can be
introduced and remain in the returned condensate,
leading to build-up on the heat-transfer surfaces and
consequent overheating;
c) if sludge in a boiler absorbs oil it can become less
mobile and obstruct circulation. Similar obstruction
can occur in condensate lines and steam traps owing
to the presence of oil which is carried forward with
the steam.
Vegetable and mineral oils cannot usually be removed
by plant commonly employed for treatment of the
make-up water.