Hi green twin
In my engines case
How is the d valve attached to rhe rod?
On the pic you got threads and nuts
I got a blank round.
Regards chris
Mystery steam engine
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In my engines case
How is the d valve attached to rhe rod?
On the pic you got threads and nuts
I got a blank round.
Regards chris
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The diameter are maybe 5 mm
I try to get a better print
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Thats about all i get
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Or possibly an oiler? - Or more likely an independent steam feed - which can be used for starting if the HP cylinder is at TDC/BDC? - using a steam valve akin to a Whistle valve (Normally closed, open only when operated momentarily)?
Yes I was thinking a Simpling valve, it's on the right side to tee off the incoming main steam feed.
Too high to be used to drain the valve chest
I'll have alook at those holes in the side of the piston valve chest.
I think I said earlier that it looked like the engine may not have been finished and that is wht the rods are not threded though some people do use grub screws to set the valve nut positions. The other thing that needs to be taken into account is that you can't get to the bottom of the valve so won't have access to any nuts to adjust the valve position, it will all need to be done from the top. That is why I have not spent time detailing the outer face of the valve.
Charles or K2 what do you think of the suggested slide valve designs, The main difference is Greentwin's has a smaller cavity so will open to exhaust a lot later than mine
Too high to be used to drain the valve chest
I'll have alook at those holes in the side of the piston valve chest.
I think I said earlier that it looked like the engine may not have been finished and that is wht the rods are not threded though some people do use grub screws to set the valve nut positions. The other thing that needs to be taken into account is that you can't get to the bottom of the valve so won't have access to any nuts to adjust the valve position, it will all need to be done from the top. That is why I have not spent time detailing the outer face of the valve.
Charles or K2 what do you think of the suggested slide valve designs, The main difference is Greentwin's has a smaller cavity so will open to exhaust a lot later than mine
Opening to exhaust late normally means back-pressure, loss of performance, etc. but on a compound... I don't know?? - If the piston has nearly reached the end of stroke, or even 10~or so degrees after BDC,,, then it is probably OK? Compounds do benefit from condensers and condenser condensate pumps that develop a vacuum on the exhaust. If the HP cylinder gets (say) 15psi, the LP cylinder may be getting 5psi or less. So may be more sensitive to back-pressure?
On the compound I regularly run, it starts "cold" - but warmed as the boiler pressure is rising, being barred until the engine decides there has been enough venting of condensate that it can start running safely (2 bottom drain s open, and top auto-drains working!). When it starts to kick, the boiler has usually reached around 10psi, but the engine really only develops a secure idle when it gets between 15 & 20psi... and it isn't venting much condensate. Then after a few more (5~10?) minutes of idling, it suddenly picks-up speed as the secondary cylinder clears its throat and starts to do some real work. At that point the steam supply can be turned down (usually boiler around 20psi, but throttled by the supply valve), or burner turned down so the supply is less than 15psi. 10 psi is adequate when the engine is off-load and well oiled, hot and running sweetly. Personally, I try and run at a turned-down burner, reduced boiler pressure and wide throttle. But a colleague runs the engine "on the throttle" (He is an OO-gauge electric motor powered train driver), when he maintains maybe 5psi over the required pressure. This (he says) means he doesn't lose pressure when he has to pump cold water into the boiler, which he does less frequently than I do. Or rather he tolerates the 5 psi drop of pressure and opens the throttle to keep the engine idling. I tend to give a single stroke of the feed pump every few minutes, rather than waiting for the boiler to be nearly empty, then pumping like Billy-O to fill the boiler!.
(N.B. Thanks for teaching that it is a "simpling" valve... I.E. it makes the engine a "simple-expansion" engine on the LP cylinder for starting, rather than being a compound!).
K2
On the compound I regularly run, it starts "cold" - but warmed as the boiler pressure is rising, being barred until the engine decides there has been enough venting of condensate that it can start running safely (2 bottom drain s open, and top auto-drains working!). When it starts to kick, the boiler has usually reached around 10psi, but the engine really only develops a secure idle when it gets between 15 & 20psi... and it isn't venting much condensate. Then after a few more (5~10?) minutes of idling, it suddenly picks-up speed as the secondary cylinder clears its throat and starts to do some real work. At that point the steam supply can be turned down (usually boiler around 20psi, but throttled by the supply valve), or burner turned down so the supply is less than 15psi. 10 psi is adequate when the engine is off-load and well oiled, hot and running sweetly. Personally, I try and run at a turned-down burner, reduced boiler pressure and wide throttle. But a colleague runs the engine "on the throttle" (He is an OO-gauge electric motor powered train driver), when he maintains maybe 5psi over the required pressure. This (he says) means he doesn't lose pressure when he has to pump cold water into the boiler, which he does less frequently than I do. Or rather he tolerates the 5 psi drop of pressure and opens the throttle to keep the engine idling. I tend to give a single stroke of the feed pump every few minutes, rather than waiting for the boiler to be nearly empty, then pumping like Billy-O to fill the boiler!.
(N.B. Thanks for teaching that it is a "simpling" valve... I.E. it makes the engine a "simple-expansion" engine on the LP cylinder for starting, rather than being a compound!).
K2
Given that the port locations and sizes are somewhat approximate, I think the best that can be done right now is to make an approximately sized valve that will function relatively well with the ports that are on the engine.
It is impossible to make exact statements about event timing with such inexact port information.
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It is impossible to make exact statements about event timing with such inexact port information.
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They make some couplings that are used to attach pulleys and flywheels to shafts, and they are slit several times, with an allen screw that pulls the pieces together and jams the coupling to the shaft.
I forget the name of them, but I have seen them.
Perhaps not exactly like this video, but you get the idea.
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I forget the name of them, but I have seen them.
Perhaps not exactly like this video, but you get the idea.
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Why would you want a Huco when there is no axial rotation?
Your valve cavity is very short and as K2 says will see a lot of back pressure. Infact on the scaled port face the inlet is opening before the exhaust.
Your valve cavity is very short and as K2 says will see a lot of back pressure. Infact on the scaled port face the inlet is opening before the exhaust.
Your valve is designed around asymmetrical ports and bridges.
I am not aware of a steam engine that had assymetrical ports.
Asymmetrical valves were common on large vertical engines, but the ports where symmetrical.
Using asymmetrical ports and bridges throws all the normal timing events out the window.
I did not plot out the valve travel vs the ports, since we don't know exactly what the port dimensions are.
The port dimensions should definitely not be asymmetrical, as far as anything I have ever seen in the old books.
You can't discuss exact inlet and exhaust events correctly if you don't know exactly where the port edges are.
Here is a plot for a Stanley 20hp engine.
I use displacement diagrams, as did many in the old days, and find them much easier to visualize than polar diagrams.
This displacement diagram was generated using a spreadsheet.
If we had exact port dimensions, we could punch that into a spreadsheet and get an exact idea of events.
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And this diagram from "Verbal Notes" gives a lot of information about events for a steam engine, which are admission, cutoff, release, and compression.
Unfortunately with a polar plot instead of a displacement diagram.
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Unfortunately with a polar plot instead of a displacement diagram.
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This is the Stanley design scaled down to give 0.2" steam ports, like on the OP's engine.
It should be noted that in order to achieve the typical events, the valve travel must be a certain minimum distance.
If the OP's engine does not have the correct valve travel, then there can be no logical discussion of typical steam engine events.
I guess the OP's low pressure cylinder could be set up for late or no cutoff, since it is a compound, which would change things a bit.
The Stanley cutoff appears to be at about 66% of the piston travel, as read from the displacement diagram.
This is a fairly late cutoff, but the Stanley had a Stephenson's link, which could be used to vary cutoff.
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It should be noted that in order to achieve the typical events, the valve travel must be a certain minimum distance.
If the OP's engine does not have the correct valve travel, then there can be no logical discussion of typical steam engine events.
I guess the OP's low pressure cylinder could be set up for late or no cutoff, since it is a compound, which would change things a bit.
The Stanley cutoff appears to be at about 66% of the piston travel, as read from the displacement diagram.
This is a fairly late cutoff, but the Stanley had a Stephenson's link, which could be used to vary cutoff.
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So it just occurred to me, if OP took measured the valve travel without his Stephenson's link being in the full gear position, then it all goes out the window.
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This is the problem with looking at old books of full size vs having actually made a few model engines engines.
You may not have seen asymmetric ports on a drawing as it is unlikely the drawings show that. As I said cored ports are seldom in exactly the position the theoretical design shows.
In some cases where you can get to the cast passages they can be evened out by milling but may not then be to drawing sizes. On this engine although it would be possible to tidy up the port faces I'm not sure if the OP has the experiance to do it so best to work with what we have so far.
If you want to look at some old plans or books then I'll post some in a while which shows how much shorter your internal cavity is to what is normal on models (and to some extent full size)
With luck full gear will give the 12mm of movement, could give a bit less in which case it will be even further from your assumed 1/2"
You may not have seen asymmetric ports on a drawing as it is unlikely the drawings show that. As I said cored ports are seldom in exactly the position the theoretical design shows.
In some cases where you can get to the cast passages they can be evened out by milling but may not then be to drawing sizes. On this engine although it would be possible to tidy up the port faces I'm not sure if the OP has the experiance to do it so best to work with what we have so far.
If you want to look at some old plans or books then I'll post some in a while which shows how much shorter your internal cavity is to what is normal on models (and to some extent full size)
With luck full gear will give the 12mm of movement, could give a bit less in which case it will be even further from your assumed 1/2"
It is hard to say if the original designer/builder adhered to typical steam engine norms, or did their own thing.
Could be either.
We are playing a bit of a guessing game, hopefully educated guessing.
Perhaps one approach would be to try and run the engine on the low pressure cylinder only with a proposed D-valve of some sort.
Anyone ever done that?
I did that on the green twin to make sure each cylinder worked well independently.
It the engine won't run on the LP cylinder, then the valve design needs to be tweeked, or else the ports are too abnormal to function properly.
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Could be either.
We are playing a bit of a guessing game, hopefully educated guessing.
Perhaps one approach would be to try and run the engine on the low pressure cylinder only with a proposed D-valve of some sort.
Anyone ever done that?
I did that on the green twin to make sure each cylinder worked well independently.
It the engine won't run on the LP cylinder, then the valve design needs to be tweeked, or else the ports are too abnormal to function properly.
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So here is a comparrison between the height of the cavity in the valve and the ports for a number of model compound engines. Note in most cases the cavity is equal to or just less than the sum of the central exhaust port plus the two "bridges" as Greentwin calls them. Quite usual model engine practice and even the Stanley is only a little under the total.
However the one by GT has a proportionally much smaller cavity which will mean the exhaust is open for far less time. Pat if you want to replot that Stanley indicator with points C & D moved to suit your valve you will get a very different plot
All have been scaled with the same proportions to suit the size of Chris's engine. From Left To Right
GreenTwin
JasonB
John Haining's ploughing engine LP valve
Stuart Turner Compound LP
Model Engineer 1924 LP Valve
However the one by GT has a proportionally much smaller cavity which will mean the exhaust is open for far less time. Pat if you want to replot that Stanley indicator with points C & D moved to suit your valve you will get a very different plot
All have been scaled with the same proportions to suit the size of Chris's engine. From Left To Right
GreenTwin
JasonB
John Haining's ploughing engine LP valve
Stuart Turner Compound LP
Model Engineer 1924 LP Valve
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