Displacement lubricator design

[JonL]

Old hat for some maybe...

I'm about to start making a displacement lubricator for my Stuart 10H / Stuart 500 Boiler combination. I was just going to knock up a fairly conventional one, but having done some reading I found out they work better when kept cool to enable the steam to condense in the housing and displace the oil. 

If thats the case, why don't they have fins or similar to keep the whole thing cooler? I don't like hanging anything off unsupported pipework so was planning to put it on a pedestal, so why not use this as a way of diverting the heat away from the main oil tank?

I figured I would also use a drain tap a bit like a cylinder drain cock to drain off the condensed water after use; if anyone has a good reason why I shouldn't then please let me know. 

[builder01]

You don't want the lubricator to cool the steam. After all, the lubricator is in the steam line before the steam gets to the engine. If the steam is completely cooled, you will be sending water to the engine. The steam that passes by a typical displacement lubricator, is just cool enough so that a very small amount of the steam turns into water and sinks to the bottom of the reservoir, displacing the oil into the steam line. If this happened very fast, the reservoir would soon be emptied. A displacement lubricator, because it is usually only supported by the steam pipe connected to it, stays at about the right temperature for it to operate correctly. Don't overthink this, displacement lubricators have been used for a very long time quite successfully, built exactly as you see them in catalogs and articles. No need for cooling fins.

David

[JonL]

Ah bum, guess what I've virtually finished this evening, a lubricator complete with modest fins....

[racinjason]

A displacement lubricator is tee'd into the steam delivery pipe and works by the steam pushing into the oil tank and then condenses and sink's in the oil so when the steam delivery is closed the oil is forced out by the small air pocket at the top of the tank. Then when the steam is applied again it forces the oil to the cylinders and also puts more steam in the tank to condense again.
Cheers Jason

[builder01]

Actually, a displacement lubricator works by the steam condensing into water and sinking to the bottom of the reservoir. The water in the reservoir displaces the oil. This is why it is called a "displacement lubricator". There is no air pocket. Any air in the reservoir will be removed by the steam.

David

[racinjason]

if there is no air at the to then the steam can't get in to condense.

[mbrown]

I think it is a combination of both processes. Some full size displacement lubricators have an internal chamber connected to the oil reservoir by a small hole so that the air in the chamber continues to push oil out when the steam is off (loco coasting) and no condensing is taking place.

Cheers

Malcolm

[Deleted]

Is the angle of the pipework not important? I know from my research on 4472 that the drawings (works) give the angle in degrees from lubricator to delivery, the info is given in detail in the RCTS tome. It's not something that I've needed to look into any further as displacement lubricators, although fitted to Great Northern when launched were very soon changed to Wakefield mechanical lubricators, I don't think 4472 ever had them when launched a year later, IIRC the reasons for the change are given in the book.

Pete

[oldnorton]

The argument centres on whether it is a cyclic system, with the inevitable rise and fall in pressure of the steam line, or a continuous one in which the steam is drawn into the oil chamber by condensation, while oil simultaneously exits.

I am completely with Jason on this! Perhaps a small amount of continuous bleed if the pipe is large - that is why an in-line jet is helpful.

Norm

[JonL]

I don't imagine my finned design has compromised anything, just keeps the oil cooler for longer, encouraging the condensing process. Or doing naff all. Either way, I'll see how this goes. My plan for the delivery pipe is to send a copper pipe through the top of the housing then use the smallest drill I have in the tailstock to prick a hole in it.

[Donald G]

May 14, 2019 11:40:10 GMT JonL said:

I don't imagine my finned design has compromised anything, just keeps the oil cooler for longer, encouraging the condensing process. Or doing naff all. Either way, I'll see how this goes. My plan for the delivery pipe is to send a copper pipe through the top of the housing then use the smallest drill I have in the tailstock to prick a hole in it.

You will definitely need a small needle valve between the displacement tank and the feed into the steam pipe. Also, you need a shutdown valve on the steam feed. Generally you leave open the shutdown valve before you start running, once on the go, a check should be made at the top of the chimney to make sure you are getting oil through into the steam. If the exhaust is very wet, then throttle down the needle valve until you just get the hint of dampness at the rim of the chimney. If you stop the loco for very long, it is best to close the feed valve to the lubricator. This will stop the flow of displaced oil to the steam pipe. Failure to do that does mean you can have oily smuts will cover you once you drive off.

All this learnt from others and my own getting a fair covering of oil when I forgot.

Donald

[JonL]

I should maybe qualify this by saying its a lubricator for a Stuart 10H stationary engine, sorry if I missed that detail out.

Here is what I'd made up until this thread started to take off. 


The pedestal base in on the right, the threaded hole for the cap on the left. The small threaded hole is the drain for the condensate.

I based it on this design; used for roundhouse locomotives.

[JonL]

It seemed a shame to waste what I had done so far so I finished it with a couple of threaded bungs and a bit of pipe. I'll make the connectors easily swapped and then I can experiment with a few variations of the design. I enjoy this sort of stuff. Next one to try will have a metering needle, I just hope it's within my current skill set. Don't know until you try...

[Jim Scott]

Hi Nobby

If you have used dimensions close to those of the 'Roundhouse' displacement lubricator yours will be perfectly adequate for your purposes without further refinement. Typically, my grandson when operating a Roundhouse 'Lady Anne' loco will drain and refill the lubricator every second gas tank refill. This is in effect 50 minutes run time which I would think would be adequate for a small stationary engines. There are no special operating, instructions, just fill the lubricator with steam oil and screw the cap on.

Just a thought - presumably the diameter of the small hole in the steam pipe is fairly critical as regards the oil delivery rate..?

I love the photo - very artistic. However, my grandson's little brother wants to know why the man has a funny 'thingy'....!

Jim S

[JonL]

As an interesting follow up... (well, I think so...)

I was recently given a Mamod SL1 by a friend; after a very brief bit of investigation I have found it to be heavily modified, including a custom regulator, water top-up valve, meths burner and a dead leg lubricator. The dead leg pipework is very long indeed; the steam pipework is under the boiler and the lubricator tank is by the smokebox. On a trial run I filled it with the correct steam oil and lo and behold, after a long run the lubricator was filled with water, and a little emulsified oil. I'm surprised this worked as well as it did; is the oil travelling along the inner walls of the pipe whilst the steam travels the centre? Does the steam pulse back and forth or just gently cycle?

Just when I think I'm starting to understand things I begin to realise how little I know...

[Roger]

Jun 9, 2019 12:58:21 GMT JonL said:

As an interesting follow up... (well, I think so...)

I was recently given a Mamod SL1 by a friend; after a very brief bit of investigation I have found it to be heavily modified, including a custom regulator, water top-up valve, meths burner and a dead leg lubricator. The dead leg pipework is very long indeed; the steam pipework is under the boiler and the lubricator tank is by the smokebox. On a trial run I filled it with the correct steam oil and lo and behold, after a long run the lubricator was filled with water, and a little emulsified oil. I'm surprised this worked as well as it did; is the oil travelling along the inner walls of the pipe whilst the steam travels the centre? Does the steam pulse back and forth or just gently cycle?

Just when I think I'm starting to understand things I begin to realise how little I know...

Just a personal opinion, but I don't think there are many facts based on proper tests to say what happens to Steam oil when it's introduced into a steam pipe. There's a lot of talk about 'atomising' the oil a long way upstream of the cylinders, but I very much doubt if true atomising occurs or whether it even matters. I suspect the oil mostly tracks along the walls and is occasionally carried along in droplets as they are drawn or thrown off at corners for example.

To my mind, the bottom line is that Steam oil is going to get thrown around and smeared everywhere as it slides, pours and drips on its way through the system. If you ask the question the other way round, and ask how you could introduce Steam oil into the system and stop it from getting everywhere, I think you'd agree that you probably couldn't do it.

I've taken this view when deciding to feed the oil into the steam chest such that it falls out of a hole in the top or smears along the wall. Time will tell whether I'm right or not, but I can't say I'm in the least bit worried about it.

[robmort]

Jun 9, 2019 12:58:21 GMT JonL said:

As an interesting follow up... (well, I think so...)

.... The dead leg pipework is very long indeed; the steam pipework is under the boiler and the lubricator tank is by the smokebox. On a trial run I filled it with the correct steam oil and lo and behold, after a long run the lubricator was filled with water, and a little emulsified oil. I'm surprised this worked as well as it did; is the oil travelling along the inner walls of the pipe whilst the steam travels the centre? Does the steam pulse back and forth or just gently cycle?

Just when I think I'm starting to understand things I begin to realise how little I know...

Just found this thread as I'm thinking of fitting a dead-leg type, and you gave some very useful information there about the length of the pipework. After a lot of research, I can find very little clear design information or experience concerning the layout and length of the pipe between the steam connection and the oil tank.

Usually these lubricators are close-coupled and the pipe is horizontal so it is assumed that the oil and steam can flow between them easily, but there is litte experience of how long the pipe can be and how much it can rise or fall. Presumably rising away from the tank is better so that the heavier water can fall into it. I suspect it will still work well with a very long pipe as you say, so how long is it in your case, and does it rise or fall or both?

Nobody knows exactly how the oil and condensed steam flow in opposite directions but it is likely the water tends to flow along the botton of the pipe and the oil above. No pulsing of stean back and forth is necessary, just the condensed stean (water) entering the pipe, being denser than oil, gradually falls into the tank.

[chris vine]

My understanding of displacement lubricators is that (if there are no valves fitted) the rate of feeding oil is determined by the rate at which the steam condenses into water and sinks to the bottom - "displacing" the oil.
How it flows along the pipe is another matter!

The point is that the rate of using of the oil is determined by the rate at which the steam condenses in the lubricator. This depends on how hot or cold the lubricator is.
In my very old Stuart Turner catalogue (1971 and read and re-read constantly as a schoolboy) it states that the lubricator must be close to the steamchest and, if I remember correctly, that it should be mounted with a copper washer so that it stays quite hot. If a fibre washer is used (again if my memory is correct) they asserted that the lubricator would be too cold and the oil would all be used up much too quickly.

Chris.

[simplyloco]

Nov 26, 2019 22:52:33 GMT chris vine said:

SNIP
In my very old Stuart Turner catalogue (1971 and read and re-read constantly as a schoolboy) it states that the lubricator must be close to the steamchest and, if I remember correctly, that it should be mounted with a copper washer so that it stays quite hot. If a fibre washer is used (again if my memory is correct) they asserted that the lubricator would be too cold and the oil would all be used up much too quickly.

Chris.

I have the same publication. You are quite correct!
John

[robmort]

Chris,

you are partly right that the "rate of using of the oil is determined by the rate at which the steam condenses in the lubricator", but it is also determined by the flow rate if a needle valve is used to limit the oil and water flows.

But where exactly does the steam condense? It does so where the temperature (of the pipe) goes below the boiling point and that, in a dead-leg type, is close to the the steam pipe junction. In any case it will occur somewhere along the pipe to the lubricator no matter how long or where it is. It then does not matter whether the oil tank is cold or not as the condensation does not happen there.

The rate at which it condenses is probably determined mainly by the size of the pipe, so a narrow pipe is preferred; in any case a needle valve is best used to regulate the flow.

Rob