Continuing on I have made the 3 Guide bars all straight forward as I have a surface grinder very easy to get them looking very nice.
Stuart Triple new build
- Thread starter Emers
- Start date
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It has been a while I have been working slowly and making some progress. I have had some paying work plus also, as I have had it said by others, you lose some enthusiasm for the project. I am back.
My last post was the making of the transfer pipes they are finished.
My last post was the making of the transfer pipes they are finished.
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Next came a real problem for me getting the model to run on air on all 3 cylinders looking at some other posts I was vey confused on what to do to get them all working on air. I noticed on some videos of others they would feed air to both the HP and LP cylinders and get the model to run OK. I could not achieve this I tried many things including making different eccentrics for the HP cylinder all to no avail, in the end I tried checking the timing after reading an article from John from johnmachines YT channel and ended up with a better understanding of how things work, not fully grasping what happens in a triple expansion engine but enough to try a few different things.
This allowed me to see that the HP cylinder was nowhere near correct and the fix for me was to set it 180 degrees from where I had it, I thought I had done enough research to have this correct but not so. The timing disc and bits were made using my laser engraver which can cut 3mm MDF easily that is how I make all my gaskets as well just draw in cad save as a DXF file and all done.
This allowed me to see that the HP cylinder was nowhere near correct and the fix for me was to set it 180 degrees from where I had it, I thought I had done enough research to have this correct but not so. The timing disc and bits were made using my laser engraver which can cut 3mm MDF easily that is how I make all my gaskets as well just draw in cad save as a DXF file and all done.
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I feel in writing mood now so on with my build progress I next made the Air pump & Water pump. Reasonably straight forward machining operations. Some pictures will show results.
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Next was the lagging of the cylinders the kit is supplied with some aluminium sheet I felt that keeping the cylinders insulated as best possible was important so I packed the space behind the lagging with bits of timber & glue before fitting the lagging. I made cardboard templates for each side then transferred to the aluminium sheet, it was very fiddly but came out well.
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Looking very good!
Please can you tell us your final settings for the valve timing? - Sounds like a bit of technical stuff I would not have expected you to struggle with, as it is just a matter of opening the next lower pressure cylinder at - or very slightly delayed (due to the 120 degree delay of the crank spacing?) - from the higher pressure cylinder that feeds it. - But I have never had to work-it-out, so it may be more complicated than I expect?
( I feel an excel spreadsheet of gas pressure analysis numerical modelling may be in order here? - something to tease the brain cells?).
I can see it is a 120degree crank, and can get suitable sizes of the Stuart model, so will have a go if I find the time.
Now to read all about it:
https://www.homemodelenginemachinist.com/threads/effective-valve-timing-for-triple-expansion.27624/
Carry on Sir! - A good thread.
K2
Please can you tell us your final settings for the valve timing? - Sounds like a bit of technical stuff I would not have expected you to struggle with, as it is just a matter of opening the next lower pressure cylinder at - or very slightly delayed (due to the 120 degree delay of the crank spacing?) - from the higher pressure cylinder that feeds it. - But I have never had to work-it-out, so it may be more complicated than I expect?
( I feel an excel spreadsheet of gas pressure analysis numerical modelling may be in order here? - something to tease the brain cells?).
I can see it is a 120degree crank, and can get suitable sizes of the Stuart model, so will have a go if I find the time.
Now to read all about it:
https://www.homemodelenginemachinist.com/threads/effective-valve-timing-for-triple-expansion.27624/
Carry on Sir! - A good thread.
K2
I found this - that doesn't explain much!
But this one says a bit more?
K2
But this one says a bit more?
K2
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Mechanicboy
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To running test for each cylinder: Remove the two connecting rod to other cylinder who is not in use (due less load caused by friction), the cylinder who is under test/adjusting timing must have connecting rod to run the steam engine. Also you are adjusting/running the triple steam engine as if it were "one cylinder steam engine". For each cylinder, it must be able to run both forward and backward when the timing is properly adjusted.
After each cylinder has correct timing and running test for each cylinder is done, mount all connecting rod and the two manifolds on place and the triple steam engine is ready to run.
Here is my triple expansion steam engine running at airpressure.
Testing the Edwards vacuumpump..
Steamingandy
Active Member
This is the method I used on the three I have done and they all ran first time, hopefully it makes sense.
Assumptions: The cams are machined to the correct throw and angles, check HP 30deg IP, LP 15deg and the cylinder ports are machined to the drawing and if not possible compensated in the valve.
set the cams to sit equally to the appropriate crank (pictures)
HP cylinder, with the exhaust/transfer pipes removed and drain cocks open feed a few pounds of air to the inlet of the valve chest.
Determine what direction the engine is turning with the expansion link in current position by turning to TDC and find the direction the valve rod drops (direction of rotation)
Turning in that direction only listen when the air just starts to enter the cylinder and make a note of the position of the crank compared to TDC now continue to turn (in direction of rotation) and note the position at BDC, these positions need to be equal, set by adjusting the length of the valve rod, just the one driving the valve.
Now move the expansion link to use the other cam, turning in the OPPOSITE direction repeat the process.
IP cylinder, attach air to chest inlet without moving the expansion link turning in the direction of rotation at TDC check the valve is DROPPING if not swap the valve rods at the link end, now equalise as before move the expansion link and repeat equalisation.
LP cylinder, attach air to chest inlet as before but remember you have now turned the engine round and last direction of rotation is reversed.
Hopefully this makes sense if not maybe I can take more pictures
HP cam setting
Assumptions: The cams are machined to the correct throw and angles, check HP 30deg IP, LP 15deg and the cylinder ports are machined to the drawing and if not possible compensated in the valve.
set the cams to sit equally to the appropriate crank (pictures)
HP cylinder, with the exhaust/transfer pipes removed and drain cocks open feed a few pounds of air to the inlet of the valve chest.
Determine what direction the engine is turning with the expansion link in current position by turning to TDC and find the direction the valve rod drops (direction of rotation)
Turning in that direction only listen when the air just starts to enter the cylinder and make a note of the position of the crank compared to TDC now continue to turn (in direction of rotation) and note the position at BDC, these positions need to be equal, set by adjusting the length of the valve rod, just the one driving the valve.
Now move the expansion link to use the other cam, turning in the OPPOSITE direction repeat the process.
IP cylinder, attach air to chest inlet without moving the expansion link turning in the direction of rotation at TDC check the valve is DROPPING if not swap the valve rods at the link end, now equalise as before move the expansion link and repeat equalisation.
LP cylinder, attach air to chest inlet as before but remember you have now turned the engine round and last direction of rotation is reversed.
Hopefully this makes sense if not maybe I can take more pictures
HP cam setting
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Hi Everyone
Thanks for the comments I ended up with the eccentrics as per the Stewart drawings, where I made a mistake was I had the HP eccentric 180 degrees out. I could get the engine to run with only the HP connected on air and turn in one direction but when I connected the IP cylinder it would not run in the same direction it was reversed and I could not work out what I had done wrong. I was following everyone's suggestions but no success, when I finally realised my mistake it was as simple as turning the HP eccentric 180 degrees and it worked.
I have made a simpling valve using the inspection plug in the intermediate valve chest to momentarily put some steam onto the intermediate cylinder to get it started when the HP cylinder is on TDC or BDC at startup. Some pictures will explain my approach. I have attached a displacement lubricator and that is the Stewart kit completed but I am going to add a condenser to utilise the air pump and water pump on the model and then I will run it on steam, have only used air to this point will post my progress on the condenser as it is being made as I speak and is coming along nicely.
Cheers
Thanks for the comments I ended up with the eccentrics as per the Stewart drawings, where I made a mistake was I had the HP eccentric 180 degrees out. I could get the engine to run with only the HP connected on air and turn in one direction but when I connected the IP cylinder it would not run in the same direction it was reversed and I could not work out what I had done wrong. I was following everyone's suggestions but no success, when I finally realised my mistake it was as simple as turning the HP eccentric 180 degrees and it worked.
I have made a simpling valve using the inspection plug in the intermediate valve chest to momentarily put some steam onto the intermediate cylinder to get it started when the HP cylinder is on TDC or BDC at startup. Some pictures will explain my approach. I have attached a displacement lubricator and that is the Stewart kit completed but I am going to add a condenser to utilise the air pump and water pump on the model and then I will run it on steam, have only used air to this point will post my progress on the condenser as it is being made as I speak and is coming along nicely.
Cheers
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Great build can you tell me where you got the drain cocks from or how you made them
many thanks
Hi
The draincocks of the side of each cylinder are standard from Stewart models.
Let me know if more information is needed
Cheers
emers
T.S. True sportsman
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Bob Sorenson
Active Member
Super nice work. From your descriptions and photos I think I could take this project on. The method you used for the crank answered a lot of questions.
thanks for that andy
i am looking to make the ip eccentrics and crankshaft out of solid bar using 2 separate throw pieces which i will align each end and help with jacking the crank to support it through making it. would you know the co-ordinances from the 120 degrees throw as i will center drill on the mill the 6 centers (each clamp) out of round bar and clamp both ends to the crank and turn between centers. hope this makes sence!!!
Regards
Andrew
Hi Andrew,
I can imagine your process. Sounds good! Aligning the throw pieces to get the centres truly in line may be "a bit of fun" - but that is what it is all about!
K2
I can imagine your process. Sounds good! Aligning the throw pieces to get the centres truly in line may be "a bit of fun" - but that is what it is all about!
K2
