Steam & Excursion > High Temperature Steam Cylinder Oils

Hi Everyone:

I would like to respond to the thread about superheat temperatures and steam cylinder lubricants. We are Lubrication Specialties Corporation of Stearns, Kentucky and we are exclusive manufacturers of Green Velvet Steam Engine Lubricants. We manufacture four different grades of steam cylinder lubricants, including our Sapon-A-Non1500 Formula 1. This lubricant contains no compounding and is rated "for superheated steam over 200 psi, 700ºF maximum temperature and with superheat in the exhaust".

The query about superheat temperatures and adequate lubrication in steam locomotives is a complex question. But, a response can be built around three primary issues. First, the superheat temperatures generated are a function of boiler's flue gas temperatures and the area of superheat surface presented to these high velocity, turbulent flue gases. Modern steam locomotives with convection type E superheaters generated total steam temperatures around 700 deg. F as noted in some of the other threads. This average temperature is corroborated by the late Ralph Johnson, Chief Engineer of Baldwin in his book "The Steam Locomotive" published by Simmons Boardman in 1942.

Second, lubrication of locomotive valve and piston packing rings and rod packings is a function of materials of construction, tribology (surface finishes and treatments) the feed arrangements (steam atomizers, quills, lubricators, etc.) and the quality and quantity of steam cylinder lubricant applied to the valve chests and cylinders. Even if all the above conditions are optimized with the best practices using the best cylinder oils, the resulting lubrication is marginal boundary type lubrication that can only minimize wear, not eliminate it. When a premium cylinder oil like our Sapon-A-Non1500 Formula 1 is applied to this type of application it will significantly extend the mileage between ring replacements, but valve ring life (in miles), especially admission rings exposed to the highest temperature steam in the steam circuit will still establish the mileage limits between ring replacements.

Steam locomotives utilize a counterlfow principle where relatively cool exhaust steam washes the cylinders and ports on its way out to the exhaust nozzle and stack. This means many surfaces requiring lubrication are at an average temperature significantly lower than the steam temperature at the superheater header. Therefore, 700 deg. F superheater engines can be adequately lubricated with mineral based cylinder oils that flash at 600 deg. F. Also, it is important to remember steam cylinders are filled with steam - not air. The lack of oxygen in steam cylinders prevents rapid oxidation in such a high temperature environment. However, the mineral base oils must remain stable at these high temperatures to avoid thermal decomposition. Green Velvet base oils come from cylinder stocks that nearly reach 700 deg. F when they hit the bottom of the atomospheric pressure distillation tower at our supplier's refinery. Green Velvet Steam Cylinder Oils, unlike competitive gear oils are formulated especially for severe high temperature applications and are not compromised by gear oil requirements for low flash additives. They are quite simply traditional cylinder oils made specifically for traditional high temperature locomotive applications.

Third, the thermodynamic realties of the rankine cycle (steam engines) suggest the battle that raged around thermal efficiency some 60 years ago is over! While theoretical calculations show improvements in efficiency can be gained with higher superheat temperatures, in practice these improvements cannot be easily achieved in a simple expansion steam locomotive. Why? Because steam locomotives must put out huge tractive efforts that limit how short the cutoff can be set while under way. This means a lot of the energy available in high temperature superheated steam is wasted up the stack because it is not completely expanded to atmospheric pressure in the cylinders. In America high work output at the expense of low fuel efficiency always governed the construction of steam locomotives because labor was (and is) expensive and coal was cheap.

Furthermore, examination of the huge temperature differential between the 2800 deg. F firebox and the 750 deg. F superheater outlet suggests an enormous loss of opportunity to convert high quality heat energy to equally high quality mechanical work. The diesel engine does not have this problem because it combusts it fuel at roughly the same temperature directly in the work output cylinders. So we can see from this comparison (called a Carnot cycle comparison) that the steam locomotive has already lost the thermal efficiency battle before the steam even gets to the cylinders!

What does all this have to do with the current threads? The current discussions about high superheat are irrelevant and counter productive because high superheat and inadequate lubrication drive today's steam locomotives off the road (where they make money) into the shop (where they cost money). At Lubrication Specialties we always recommend reasonable superheat temperatures that allow efficient lubrication with mineral based cylinder lubricants. Or we recommend saturated steam on low load factor operations so compounded oils can provide even better lubrication. The primary objective is to generate maximum mileages between overhauls and replacements. This is the area that can drive today's steam locomotive costs down significantly. The miniscule fuel savings possible with increased superheat will quickly be swallowed up by the corresponding huge increase in maintenance costs.

William Petitjean, P.E.

Thank you for that excellent tutorial on superheated steam and the lubrication challenges it poses. I can vouch for everything you have said based on our real life experience with C&O614. When we return her to service we will certainly seek you out and give your high quality oil a try.
We also intend to shorten the length of the superheater tubes so as to lower the steam temps from a current 750-800 to 650-700 for the very reasons you explained so well.
Thanks again for sharing your knowledge.
Ross Rowland

Thanks for the information. I proves again that when I need to know something that is railroad related I can always count on Trainorders.com.

I believe modern steam power plants run their turbines at much higher pressures and temps. Does their bearing design not put the same stress on lubricants? How about throttles? Are they also designed to avoid the same lubrication problems?

Hi Doug:

You are correct. Large central generating station steam turbines utilize inlet steam at much higher pressures and temperatures than simple expansion steam locomotives. However, the thermodynamic key to their success is multiple pressure and velocity staging that allows them to expand the inlet steam to very low absolute exhaust pressures. These machines convert the maximum amount of heat energy in the steam into useful work (electricity generation).

Many of these turbines are, in effect two turbines side by side - called cross compound turbines. These machines expand their steam through something like 28 or more stages, whereas the typical two cylinder steam locomotive only expands its steam through one simple expansion stage. Locomotives are unique because they produce enormous work outputs in a relatively small package that can fit the railroad's loading gauge. The turbines you reference are housed in enormous buildings.

Steam turbine bearings are outside the steam environment and are not subject to the severe turbulence and washing action such as found in steam locomotive cylinders. Furthermore, the operating temperatures of large turbine shaft bearings are controlled by constant re-circulation of low viscosity turbine lubricating oils that are run through cooling systems to maintain the bearings at a reasonable temperature. These bearings are designed to operate in the dynamic lubrication mode where the lubricants generate a "wedge" that completely separates the journal from the bearing. This is far superior to the boundary lubrication mode found in steam locomotive cylinders.

Throttles and linkages are low speed, oscillating mechanisms that require little lubrication of any kind and generally are not a lubrication problem unless they become sticky and hard to move. However, most governor throttles on large steam turbines are actuated by servos motors that usually have plenty of power to control the throttles.

Thank you for your repsonse. I hope this clarifies these issues for you.

William Petitjean, P.E.

Thank you, Mr. Pettijean for your concise, clear explanations on cylinder lubrication. All of your info has really set the (square) wheels in my mind turning and I have a few questions and ruminations. First, it sounded as if Green Velvet is now producing only the 4 mineral based grades and not the synthetics. Is this true? Also I noticed from your specs that the synthetic base stock has a flash point at least 45 degrees F lower than your top mineral grades. Is this not a problem simply because the carbon residues of the syns. are "negligeble"? I must say I agree with your analysis that higher superheats in a simple expansion engine are a red herring. To my thinking, any great amount of superheat left in the steam as it exits the exhaust nozzle is simply wasted energy. But I now want to turn to the subject of compound locomotives. In France, Chapelon found he had to raise superheat temps at the header to 400 degrees C (and I assume he was talking 400 over the saturation temp at boiler pressure) in order to have 100 C of superheat left over at the LP steam chests. I believe that tranlates into something north of 900 F. Is ther any oil, natural or synthetic that will stand up to that? I believe Chapelon may have had an answer, but one that presents another problem. It is found in his experimental loco 160A1, a 2-12-0. The type A superheater flues were split between regular elements for HP steam and dual "single pass" elements in the circuit between the HP and LP cylinders. This double the cross sectional area for LP steam flow, necessary as steam volume had been at least doubled from the HP side. Also, all cylinders were jacketed I believe with with boiler pressure saturated steam. On test he found that fuel economy only dropped 1% when the HP cylinders were fed saturated steam, but only if the steam jacket were maintained, avoiding cylinder wall condensation. Constructed this way steam would be at sat. temp in the HP cylinders and would only need to be raised to 550-600 F in the intermediate superheater. Lubrication problem solved...except for one thing. A 10% compounded oil would have to be used in the HP cylinders and this would carry over into the intermediate superheater. There the Saponified oil would undoubtedly stick to the interior walls of the elements, which would be much hotter than the steam within. That heat would simply vaporize the water in emulsion and the compounding elements of the oil. The problemis the surface temp of the inner tube walls would also be high enough to carbonize the remaining oil, particularly since the oil sticking to the surface would act as an insulator, slowing down heat tranfer to the steam and thereby raising the wall temp even higher. It seems to me the tubes would become coked up and inoperable in relatively short order, especially at high outputs. Yet there is no mention of a problem by Chapelon or anyone else commenting on his 160A1. Perhaps he had a solution I'm unaware of. If someone knows, please enlighten me.

Now, a short note to Mr. Ross Rowland:
Many thanks, sir, for your efforts at keeping the Magic Dragons out and about over these many years. It's good to hear 614 may be seen and heard at full warcry again soon. But after reading the previous posts, may I offer a possibility. To lower the steam temps consider converting the type E to single pass elements, cutting the E tandems into singles and reconnecting the ends to the header tubes. At their present length this should give temps around 625-650 F, but would double the cross sectional area of the steam circuit through the elements with proportionally greater steam flow at lower pressure drops than as built. The header tubes would also have to be resized to match that area. I believe this would result in a noticeably livelier loco that would be just as efficient as "as built", even with the lower degree of superheat.

Thank you for your time
I'll get off the soapbox now.....NEXT!

Groucho