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[Underpressure]

Why is it that manufacturers and retailers insist on posting videos of their engines working on compressed air?

I used to have quite a lot to do with the Cheddar Models factory and in all the years I visited, I never saw them test a single engine or run an engine on air. I know it is convenient at shows and demos, and I have seen some big impressive locos demonstrated that way, but there is a clue in the name of the products, they are steam engines, they run on STEAM!

When I visit a manufacturers or retailers web site, if there is a video, I want to see the product in steam and preferably in a model and being worked, yet another video of yet another engine being bench run, with no load, on air does NOT inspire me to buy.

Last rant, then I'll get off this soap box: You can not, not NOT bed an engine in on air. You certainly can bed in reciprocating parts of the engine lower down, but unless the engine is at working temperature, then you are not getting either the forces or the friction you would get under normal circumstances. This does not come just from my involvement with steam, but from many years of engine building and development work on motorcycles and cars, including racing machines.

Whew! And breathe, count 1,2...3...4...think happy thoughts think happy thoughts......

[gondolier88]

Can't agree more- however air is a convenient way of showing engines working, and to test timing etc it's cheaper than firing the boiler up. As for running in I always run in on steam- however many don't and seem to get away with it- perhaps it doesn't matter too much at model sizes- especially as a lot of pistons are O-ring sealed too.

Greg

[kno3]

I agree that running the engines on steam shows the prospective customer much more then running on air. For instance, air doesn't show if the engine leaks or not.

By the way, could you please elaborate on running an engine in on steam? For how long, what rpm etc.

[Underpressure]

Running in is al about getting frictional surfaces to bed together. I don't own any slide or piston valve steam engines, so I can only tell you what I was told some time ago. I run any engine reasonable gently until it gets to full working temperature, I make sure that the cylinder to standard mating surfaces are well lubricated and run the engine across a range of speeds, both forwards and backwards. What I don't do is try to run at high or very low speeds, just gently vary between medium slow to medium fast for about 20 minutes, dripping a little steam oil on the mating faces. I then let the engine get stone cold before I repeat the process. The very slow running of the engine will tell you when things are settling in.

After I have bench run the engine two or three times, I start to use it, conscious of the fact that it is a new engine.

This method is not definitive, I'm sure others do it differently, but the Puffin I built and bedded in using this method in 1992 is still as good as new and producing as much power as it ever did.

Neil

[HS93 (RIP)]

cheddar would advise two or three boiler fills keeping at low speed with occasional up to half and back again  letting it cool between runs and loads of STEAM OIL over all moving parts as I have said before if it is new or never run after paint don't touch the paint till it bakes on and cools, I have never heard them recommend a steam engine to be run on air .  but that would be a air engine and never driven by an out side source if it where to hydraulic through oil it would be toast.

peter

[Bunkerbarge]

Interesting points Neil and I agree it does seem to be getting more and more common nowadays to see steam engines running on air for such things as display purposes and shows, which is obviously driven by convenience.  I have an assembly of four different types of engine on a base that we demonstrate at shows using a compressor. 

Use of gas and boilers not only being a pain to maintain at pressure all day until such point as someone wants to see the engines turn but it also gets you into the areas of boiler testing and certification and gas tank testing that seems to all too often cause show organisers to throw up thier hands in horror.

As for running in, as you say it is a convenient way of running in the running gear of the engine without having to keep a boiler up to pressure throughout the entire process but as to whether it is or isn't effective at running in the cylinder faces is probably debatable.  I agree with older vehicle engines running aluminium pistons in cast iron liners and cast piston rings the process was considerably more critical than it is nowadays with the more commonly used magnesium alloys having considerably lower coefficients of expansion and therefor less sensitive to the differences in temperature.  It is also, of course, critical with vehicle engines to run normally to ensure that the firing pressures maintain the correct force on the piston ring face, thereby ensuring correct pressure of the mating faces for bedding in the parts.

As to whether this relates to the brass components of the model steam engine piston which is invariable sealed by an 'O' I'm not so sure.  I wouldn't like to comment on just how much the difference in temperatures affects the fit of these parts or just how much that change in fit will be absorbed by the piston 'O' ring but I suspect it may have very little effect on the running clearance.  I also don't know if there would be any difference in the behaviour of the 'O' ring under steam or air so whether that would play a part in the pressure on the cylinder wall but it would certainly be interesting to see just what information there may be around somewhere to demonstrate this.

I really don't think there is a right or a wrong with a lot of this and whether an engine should be run in on air or steam is perhaps not as significant as making people realise that some method of running in is required.  I always use air to start the process but do not consider the engine as ready until it has had a couple of runs on steam as well but to me it is a convenient way of bedding in the running gear and starting the process of flattening the face of the 'O' ring.  Running on steam takes it to the next step.  So to me saying you can not bed an engine in on air perhaps isn't looking at the whole picture.

It would be an idea though to advocate an increase in the use of boilers in demonstrations and certainly in on-line videos.  Surely part of the attraction is watching the whole plant, including the steam emmitting from the funnel, rather than just the engine turning over.

I also know of others who have started the running in process of a Puffin on air, again now running for many years, so I think the main message to get across is how important it is to do an initial running in process.  I actually know of many stories from a number of model steam engine manufacturers which have arisen out of discussions with them over the years of people who have returned badly damaged engines demanding money back but when it is investigated fully it turns out they have flashed up the boiler and instantly started to thrash the engine around the pond at full speed.  There is the more worrying one of the modeller who did not realise that the lubricator was for putting oil in as well but that's getting off the point.

Maybe we should all do some videos of our engines under steam and get them on You Tube to redress the balance a bit!

[Underpressure]

Bunkerbarge, I agree that at shows and demonstrations compressed air is both more convenient and arguably slightly safer, it certainly requires a lot less attention and allow the exhibitor to concentrate on talking to the 'punters'. That said Cheddar used to have a demo plant which had the propeller turning in a fish tank, connected to whichever plant it was they were promoting, more usually the Proteus after it's release. The plant would happily tick tock away all day long, using the ABC system to reduce the gas when not needed. My complaint is not about these situations, but more about the growing trend on retailer / manufacturers web sites of showing video's of the plant in action. A few do use steam, but many don't and as for showing the plant actually installed in a boat, on the water...that one is a real rarity.

As for running in, piston to cylinder clearance is only one point of bedding, and on a steam engine I would agree that it is one of the least critical areas. However, on an oscillator the more crucial area is the face between the cylinder and the standard, as well as the regulator valve. On a valved engine there are all the moving parts of the valve gear. All these areas get to steam temperature and obviously clearances change, especially if there are different materials involved, a bronze slide valve moving in an iron chest for instance.

There are of course many ways of getting the job done, but the trend towards air and away from steam is, in my opinion, a bad one, IF (and it's a big if) the engine is ever to be used under load.

Neil

[kno3]

...

Maybe we should all do some videos of our engines under steam and get them on You Tube to redress the balance a bit!

Here's my attempt: the second run of my Graham TVR1A, the boiler used is a Cheddar Puffin return-flue.
http://www.youtube.com/watch?v=Gv05K6qeTkk

[Underpressure]

STEEEEEEEEEEEEM 

[Bee]

Make the most of it. In a few years it will just be a 3D CAD animated rendering. Some places already just use that for the stills. And they do look good, no scratches or machining marks, but I bet someone is working on simulating a 'used' look to perfect the illusion.

[Underpressure]

Make the most of it. In a few years it will just be a 3D CAD animated rendering. Some places already just use that for the stills. And they do look good, no scratches or machining marks, but I bet someone is working on simulating a 'used' look to perfect the illusion.

Miniature Steam in Australia already have 3D CAD Video, which is even worse than compressed air 

[gondolier88]

Can I just point a couple of things out that may be a little contraversial to a few on here-

1- ANY CNC made machine at any scale should not need running in for correctional purposes- ie 'taking up' bearings/ surfaces etc- only gentle running for the first few ten thousand revs- a CNC machine will machine to a tolerence far more accurate than any engineer could hope to do again and again- when assembled a good oil with LIGHT oil for the bearings and cylinders changing to STEAM oil in the CYLINDERS only  when upto temperature and after 10,000 revs or so- about 5-6 mins running.

2- Regarding cylinder oil- at 50psi, running at 800rpm a twin cylinder oscillater with O-rings will NOT produce enough friction to sieze if you ran it without oil for hours- saturated steam at that pressure will self lubricate the cylinder as it is a good 15% or so moisture- steam oil only adds to this lubrication- most displacement lubricators feed far too much far to quick anyway. Before any of you say 'codswallop' or something similar I know of two full size engines that run at under 80psi and have NO cylinder lubrication whatsoever!

The bearings are the most important things to keep lubricated at any size.

Greg

[steamboatmodel]

I prefer running the engines on steam, but at some shows it is ether not allowed or very impractical. If you must run on air remember to lubricate the engine as the steam oil is not working at that low a temperature, Air tool oil works well.
Regards,
Gerald.