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Post by suctionhose on Nov 27, 2019 2:26:04 GMT
there needs to be a space above the oil outlet for steam to enter the tank and sit there until it condenses. condensate stays in the tank displacing oil which finds its way out. there's no 'flow velocity' per se, so the two different substances can move in opposite directions. Pressure pulsations undoubtly help. The important thing is the space for steam above the oil. A full size hydrostatic has this chamber separate and above so the weight of condensate pushes oil out the nozzle. it's all at the same pressure inside...
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,909
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Post by JonL on Nov 27, 2019 20:19:41 GMT
Interesting stuff.
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mbrown
Elder Statesman
Posts: 1,720
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Post by mbrown on Nov 27, 2019 22:09:52 GMT
I like the new avatar photo Nobby! Is your middle name Barry?
(Sorry, couldn't resist it!)
Malcolm
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Post by David on Nov 28, 2019 0:16:21 GMT
My red loco has what I guess is a dead leg displacement lubricator - it has one steam pipe going in but not through it. It also has a needle valve. It is probably the same as Jason is describing. There is an air gap at the top so it cannot be filled completely with oil - the filler bush projects down into the tank to ensure this.
The 'straight through' design seems more obvious in operation but mine works well.
The lubricator steam pipe is connected to the main steam pipe where it forms a T from the regluator to branch to each side. The lubricator pipe is pointing downwards at an angle (so not directly at the ground) and has many bends along to way to get to the top of the lubricator on the running boards. So it is twisty and has a fairly sharp curve to get from the inlet T - a large trough.
Despite that torturous route the oil does get from the lubricator to both cylinders. It doesn't look like there is a need to worry about the length or orientation of the pipe(s).
The only problem mine has is the filler bush looks to be 1/4x40 thread, the steam pipe is right below it, and there is nowhere for air to escape except out the same hole. Filling it with steam oil is a real challenge and takes forever. I've just bought some syringes to see if that helps but they probably need some tubing on the end to get the outlet below the steam pipe. So be sure you can fill and drain it easily or it's a real annoyance. I have another one about 3/4 of the way finished just to solve this filling problem (I was making it once the new workshop had a roof but no walls yet!) but once the workshop was done I went back to the mogul and the parts are in a drawer awaiting the next major overhaul of the red loco.
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Midland
Elder Statesman
Posts: 1,870
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Post by Midland on Nov 29, 2019 11:41:30 GMT
there needs to be a space above the oil outlet for steam to enter the tank and sit there until it condenses. condensate stays in the tank displacing oil which finds its way out. there's no 'flow velocity' per se, so the two different substances can move in opposite directions. Pressure pulsations undoubtly help. The important thing is the space for steam above the oil. A full size hydrostatic has this chamber separate and above so the weight of condensate pushes oil out the nozzle. it's all at the same pressure inside... You have taught me something here. I had been told that the steam goes in the bottom of the tank and condenses and the oil comes out of the top of the tank under pressure. So the condensed steam falls through the oil to the bottom. But if one takes the oil from the bottom of the tank surely all there is there is water. D
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Nov 29, 2019 21:07:29 GMT
there needs to be a space above the oil outlet for steam to enter the tank and sit there until it condenses. condensate stays in the tank displacing oil which finds its way out. there's no 'flow velocity' per se, so the two different substances can move in opposite directions. Pressure pulsations undoubtly help. The important thing is the space for steam above the oil. A full size hydrostatic has this chamber separate and above so the weight of condensate pushes oil out the nozzle. it's all at the same pressure inside... Unfortunately this is a myth that seems to be perpetuated on these threads. No space above the oil is needed and the steam does not enter the tank. Instead it condenses at the entrance to, or just inside, the dead-leg pipe where the temperature becomes lower than the boiling point. Capillary action in the pipe then makes the heavier condensed water flow along the pipe to the lowest point which is the bottom of the oil tank, displacing the lighter oil. No pulsating of steam pressure is needed either.
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Nov 29, 2019 21:13:41 GMT
My red loco has what I guess is a dead leg displacement lubricator - it has one steam pipe going in but not through it. It also has a needle valve. It is probably the same as Jason is describing. There is an air gap at the top so it cannot be filled completely with oil - the filler bush projects down into the tank to ensure this. The 'straight through' design seems more obvious in operation but mine works well. The lubricator steam pipe is connected to the main steam pipe where it forms a T from the regluator to branch to each side. The lubricator pipe is pointing downwards at an angle (so not directly at the ground) and has many bends along to way to get to the top of the lubricator on the running boards. So it is twisty and has a fairly sharp curve to get from the inlet T - a large trough. Despite that torturous route the oil does get from the lubricator to both cylinders. It doesn't look like there is a need to worry about the length or orientation of the pipe(s)... David, Thanks, that's an interesting confirmation of the robustness of the simple dead-leg design and how un-fussy the pipe layout can be.
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Post by suctionhose on Nov 30, 2019 9:50:00 GMT
there needs to be a space above the oil outlet for steam to enter the tank and sit there until it condenses. condensate stays in the tank displacing oil which finds its way out. there's no 'flow velocity' per se, so the two different substances can move in opposite directions. Pressure pulsations undoubtly help. The important thing is the space for steam above the oil. A full size hydrostatic has this chamber separate and above so the weight of condensate pushes oil out the nozzle. it's all at the same pressure inside... Unfortunately this is a myth that seems to be perpetuated on these threads. No space above the oil is needed and the steam does not enter the tank. Instead it condenses at the entrance to, or just inside, the dead-leg pipe where the temperature becomes lower than the boiling point. Capillary action in the pipe then makes the heavier condensed water flow along the pipe to the lowest point which is the bottom of the oil tank, displacing the lighter oil. No pulsating of steam pressure is needed either. Well there you go... I guess Detroit had it wrong all these years.
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Post by David on Dec 1, 2019 2:36:00 GMT
Instead it condenses at the entrance to, or just inside, the dead-leg pipe where the temperature becomes lower than the boiling point. Capillary action in the pipe then makes the heavier condensed water flow along the pipe to the lowest point which is the bottom of the oil tank, displacing the lighter oil. In my case the lowest point of the pipe is a trough below the level where the lubricator pipe joins the steam chest inlet T and the rest of the lubricator pipe travels a long way upwards to the top of the lubricator mounted on the running boards - probably an 80mm different in level. Are you saying capillary action makes the water travel all that way? That trough in my lubricator pipe must be filled with water though like the loop below a pressure gauge. That would happen at least every time I shut off steam and any nearby steam condenses. So it makes sense the entire pipe is filled with water aside from the first short downwards run from the T and maybe even that is too. So how does the steam oil make its way along this water filled pipe? I've often wondered that about the ones where a drop of oil goes through a sightglass too.
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Dec 14, 2019 23:27:56 GMT
In my case the lowest point of the pipe is a trough below the level where the lubricator pipe joins the steam chest inlet T and the rest of the lubricator pipe travels a long way upwards to the top of the lubricator mounted on the running boards - probably an 80mm different in level. Are you saying capillary action makes the water travel all that way? That trough in my lubricator pipe must be filled with water though like the loop below a pressure gauge. That would happen at least every time I shut off steam and any nearby steam condenses. So it makes sense the entire pipe is filled with water aside from the first short downwards run from the T and maybe even that is too. So how does the steam oil make its way along this water filled pipe? I've often wondered that about the ones where a drop of oil goes through a sightglass too. David, That's an interesting example and a diagram would help to understand your case. But yes, capillary action will help to make the oil and water travel each way by ensuring that the liquids flow along the walls of the thin pipe, and that is how these dead-leg lubricators work, as has been shown by several examples on this forum and elsewhere. The length of the pipework and the relative heights of oil tank and feed pipe seem to make little difference as capillary forces are strong enough to overcome the resistance effects in models. Your 80mm height difference is quite large and shows that this need not have any adverse effect. The steam oil makes its way along the water-filled pipe helped by capillary action, but mainly because water also makes its way by capillary action in the opposite direction to the oil tank where it displaces the oil, due to its greater density, and forces the oil out. This is a siphon effect so the relative positions of oil tank and end-feed are not critical.
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Post by suctionhose on Dec 15, 2019 21:06:45 GMT
Your 80mm height difference is quite large and shows that this need not have any adverse effect. The steam oil makes its way along the water-filled pipe helped by capillary action, but mainly because water also makes its way by capillary action in the opposite direction to the oil tank where it displaces the oil, due to its greater density, and forces the oil out. This is a siphon effect so the relative positions of oil tank and end-feed are not critical. This may come down to a difference in understanding of the word "capillary". Capillary appears to mean the drawing of liquid along a path due to interaction between the liquid an the tube, bristle, wick etc. The displacement lubricator works on the well known effect of density i.e. oil floats on water. If you put water into the oil tank in a way that it can't escape, the oil will be floated out. The water from condensed steam can come from a long pipe, a short pipe, condensation in the oil tank itself, a condenser above the tank a la Detriot, Nathan, etc and likely many other ways... The key is that the water has to end up in the oil tank with no means to get back out again. What can the oil do but be floated out along the same path? This is simply displacement due to a difference in density. No doubt capillary and surface tension can be observed at play somewhere but I don't believe they are the fundamental principles of operation. Oil feed rate is controlled by throttling the oil's escape with a valve or orifice to frustrate the process. But nothing is more certain that the water will win over the oil. Even if the pipe was 10 ft tall, once it fills with water, the oil will be on top and be the first to spill over... (BTW a locally made displacement lubricator was governed for feed rate by drilling a #80 hole (0.013") and putting a 0.012" dia wire in the hole.)
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Post by David on Feb 22, 2020 9:59:30 GMT
While the red loco was on the bench I remembered this thread and took some photos to show what sort of pipe run you can get away with. The lubricator is reliable as long as you let enough steam into it via the needle valve (or enough of an opening for oil to get out?)
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