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Oil inside the condenser

Posted: Tue Jul 16, 2019 2:26 pm
by Ramón
Hey everyone,

I've always wondered about the effects of oil inside the condenser. As far as I've read, all condensing steam launches use the hotwell to separate the oil from the condensate. So, the oil is only removed after the condenser.

But I've been wondering if it wasn't better to remove the oil before it enters the condenser since it effectively works like a strong insulator as you know if you read about boilers.

I've read an interesting article about oil separators in condensing steam cars using different systems like using centrifugal forces, baffle plates and a reduction of steam speed to keep the oil drops inside the separating element.

So, my questions would be to what extend oil inside the condenser reduces its effectiveness and how big the differences are separating the oil before and after the condenser.

Re: Oil inside the condenser

Posted: Wed Jul 17, 2019 1:56 pm
by fredrosse
Oil separation in exhaust steam can be very effective, assuming the design of the separating device is correct. However these devices also separate water (exhaust steam wetness) from the exhaust stream, which is significant in our steam launches. IFF the exhaust steam is superheated, then effective oil separation could theoretically be achieved without capture of exhaust wetness, but I have never seen dry exhaust steam for our applications.

In any case, some oil would get through the exhaust separator, and oil/sludge will build up on the condensing surfaces. So it is just a case of longer running times before oil fouling begins to seriously deteriorate condenser performance. Quantification of how oil fouling effects performance involves many other parameters, such as condenser heat transfer design, cooling water flows, air inleakage to the condenser, and vacuum pump performance. One condenser could have degraded performance in a few hours running time, while another would run for hundreds of hours before the same performance degradation would be noticed, each condenser getting the same amount of oil contamination.

Re: Oil inside the condenser

Posted: Tue Jul 23, 2019 10:18 am
by Ramón
Interesting. I intend to try out different oil separation methods with my engine on a kind of test series.

So what you are saying implies the condenser regularily gets washed out to get the pipes clean again? I am asking because I've never read anything adressing this issue anywhere.

Re: Oil inside the condenser

Posted: Tue Jul 30, 2019 11:04 pm
by steamdon-jr
are you running a superheater or dryer? does your engine have a typical D slide valve? Reason I ask is general practice on marine steam even on large ships was no oil in the cylinders and let the steam create an isolator if you will between the cylinder and piston. We did not run any oil on our first steamboat Adelaide which had a "single cylinder 2-1/4 X 3-1/2 antique unknown maker" for 20+ years, The new boat Phoebe Snow has a Pearle "Twin" and has piston valves so we do use oil. Do you need to run oil ? I would prefer to run saturated steam and no oil if condensing, just easier and obviously safer for the boiler.

Re: Oil inside the condenser

Posted: Wed Jul 31, 2019 2:26 am
by Lopez Mike
Explain please the reason to use oil with piston valves. I have a piston valve with no oil. Is disaster impending? Joking.

Re: Oil inside the condenser

Posted: Wed Jul 31, 2019 11:15 pm
by fredrosse
"Explain please the reason to use oil with piston valves. I have a piston valve with no oil. Is disaster impending?"

Solid piston valve spools, operating in valve cylinders having port passages symmetrical around their entire circumference, produce no side thrust, and can therefore need virtually no oil lubrication. Without this symmetry, piston valves will have some small side thrust, but still far less than a typical unbalanced slide valve. For these conditions, a piston valve can get away with no oil lubrication. However there is a tendency to have piston valve leakage unless the piston valve fit clearance is very small.

Piston valves can be fitted with small piston rings (snap rings the same as typical main cylinder piston rings), and this eliminates the leakage associated with solid piston valve spools, but then steam pressure can get behind the rings, forcing them outward hard against their cylindrical seat, and thus require oil lubrication, or scoring of the valve cylinder surface may result. The same may be stated for the main power piston, generally at least twice the diameter of the piston valve.

On large engine practice there have been cleaver features to limit the ring expansion here, and the result can be a nearly perfect piston valve seal, (or main piston seal) without the ring/cylinder scoring problem, even without oil lubrication. However this type of solution is very difficult on our small launch engines, so we are generally required to accept somewhat leaky solid piston valve spools with no oil lubrication, or ringed piston valve spools that will require oil lubrication.

All of the above paragraphs are in reference to an operating engine, but now look at the piston/cylinder conditions with the engine NOT operating. If oil is present during layup, then the oil provides corrosion protection coating for the idle parts, if not, un-lubricated surfaces, or surfaces just lubricated with water, will corrode if made of iron, or, worse yet, ordinary steel. So even if you have an engine setup to work without oil lubrication for the steam wetted parts, you need to be sure to have some oil injected on the rubbing surfaces when shutdown, and this oil should be cleared from the engine before it would wash into the condensate system and boiler on startup.

Ideally we should use fully corrosion resisting parts that accept sliding contact with the minimal lubrication as provided by wetness in steam. This material is "Un-obtainum", is very expensive, and is only found on the planet "Pandora".