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Author Topic: Fine tuning a D10  (Read 1840 times)

jpdenver

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Fine tuning a D10
« on: September 08, 2017, 03:41:40 AM »

Greetings from this side of the pond.
One thing about being in Colorado is that we do not get hit by hurricanes!

I hope that those mayhemers located down in the islands are safe from Irene.

Now to business -

I built a D10 last year, and then this year I have been adding the reversing gear.
I read very carefully the thread from George, and used his flat linkage setup.
It worked out pretty well.

I have still to finish up the linkage, since it will be going in a boat, I may not use the
handle provided, instead I will be making up my own.

I have attached a picture.

The issue I am having is that I think I am getting "blow-by"

First, I followed the plans and put the three oil grooves on the pistons rather than a
ring.  I did not have any rings to use.  I am using air for the moment, and
only running for less than a minute.  I squirted in some oil, and I see a little
dripping from the exhaust, so I think I should have adequate  lubrication.

But I get a steady stream of air out the exhaust, on very low pressure,
once the engine starts, the stream continues but also puffs like I would
normally expect. 

So - I started looking at o-rings, and I am curious about what size
I should get.  I need to reverse engineer as the pistons and cylinders are
already done. 

I have found a good source I think - not the local DYI store but instead:

http://www.theoringstore.com/index.php?main_page=index 

Also what type is favored? PTFE? Silicone? other?
What size cross-section?  1/16", 1/8"

All advice is appreciated.

Thanks,
Jim Pope
Denver, Colorado





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derekwarner_decoy

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Re: Fine tuning a D10
« Reply #1 on: September 08, 2017, 05:07:33 AM »

Morning Jim......that reversing gear looks fine O0

With respect to O-Ring selection, both VITON and Silicone elastomer are technically rated by the manufactures to 200 degrees C, however above say 180 degrees C +, both suffer from greatly reduced mechanical strength and are really only suitable for static applications at these temperatures

Your 3 Bar boiler rating will provide steam at ~~ 143 degrees C, so either elastomer will be suitable in the dynamic piston application, they are also both fully compatible with steam and gear oils so there are no issues here

{burnt VITON elastomer carries the MSDS warning in the creation of hydrofluoric acid, however careful use should never create such a scenario}

Both VITON and Silicone elastomer O-Rings are usually available in 70 Duro and are easily stretched over a piston to the O-Ring groove. The O-Ring groove geometry and dimensions should be as per the manufacturers specification and relative to the bore dimension

A 1/8" section O-Ring when pressure energised and deformed will present a longer friction sealing lip that a 1/16" O-Ring

PTFE elastomer is certainly suitable for the above temperatures, however the elastomer has no memory so the piston requires to be a two piece construction to enable installation. The alternative to this is expanding and resizing cones & bushes ....more expense for a one [1] off build

Virgin PTFE has  a very low mechanical strength, so manufactures add fillers to improve or increase strength and resistance to extrusion. It can be difficult to understand or obtain a round bar of PTFE with a hardness in the range of 70 to 90 Duro

Come back with the actual cylinder bore diameter &  the piston diameters & height........from there we could look at an O-Ring nomination

Derek 
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rhavrane

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Re: Fine tuning a D10
« Reply #2 on: September 08, 2017, 07:20:35 AM »

Bonjour Jim,


Alternative 2 : Teflon sefment http://www.vapeuretmodelesavapeur.com/trucs/index.html#segment
Alternative 3 : Pston with Teflon cup http://www.vapeuretmodelesavapeur.com/piston/index.html
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pendlesteam

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Re: Fine tuning a D10
« Reply #3 on: September 08, 2017, 09:27:02 AM »

Ive built quite a few engines and dont favour O rings in pistons for the simple fact that they offer very little in the way of abrasive resistance to wear and simply are not designed for this application. For any piston under 1" dia I have always used graphite yarn, its easy to fit, cheap and gives a good seal, made all the better by hot steam. The width and depth of the 'ring' groove is not critical and I know of locos which have run every weekend for 30 years with the same packing in them. And yet no one seems to have mentioned it? My experience is from high speed engines fitted to model locos where a strip down can be a mammoth task (inside twin pistons for example) so reliability is paramount. Just a thought....
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aeronut

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Re: Fine tuning a D10
« Reply #4 on: September 08, 2017, 01:00:49 PM »

I would only add that it's probably worth getting the whole lot up to working temperature on steam before you do anything else.  You may well find that blowby is greatly reduced when all up to temp.
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IanJ

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Re: Fine tuning a D10
« Reply #5 on: September 08, 2017, 06:36:36 PM »

Hi' Interesting comment from 'Pendlesteam' regards graphite yarn to seal pistons. I saw this specified on a drawing for a small static steam engine only recently. My only experience of graphite yarn is as gland packing in stuffing boxes, so was about to ask for others opinions regards this application. How do you fit it? I assume it is simply wrapped around the groove then the piston inserted into the bore. How much needs to 'packed in'?


Ian
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pendlesteam

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Re: Fine tuning a D10
« Reply #6 on: September 08, 2017, 06:46:17 PM »

Hi Ian. To elaborate...Graphite yarn comes in different sizes ranging from a type of thin string right up to  1/2" square in cross section. If you were to buy 1/8" square you simply machine your ring groove a tad over 1/8" wide and a tad under 1/8" deep. You splice the cord at 45 degrees each end being sure it is a good overlap and simply squash it into the groove. Slightly Chamfer the piston bore end to help the packing into the bore and its done. It is easy and very long lasting.
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IanJ

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Re: Fine tuning a D10
« Reply #7 on: September 08, 2017, 06:58:09 PM »

Hi, Thanks for reply. Simple when it's explained. Are you able to suggest a supplier of square section packing that small. Many many years ago industry had experience of packing of I/4" and much greater for all sorts of applications such as valve stems, pump glands, etc. but never had the need to use any thing that small.
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jpdenver

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Re: Fine tuning a D10
« Reply #9 on: September 10, 2017, 03:30:33 AM »

Thanks for all the input.

I opened the heads and found they have dried out.
Obviously the cause of my blow-by.
Since the engine has never run on steam yet, and was sitting on the shelf
for a while, it does not really surprise me.  I added some steam oil and sealed it back up.

It started to act better, still under air, but ran well at low pressure - both directions.

Next I will finish up a steam plant - and see if heating it up increases the seals.

I made a movie:

https://youtu.be/-yALyraHIds 

There are a few points that bind, so a little some fine file work is in order.

I'll post some more when I get it hooked up to live steam.
Then I can evaluate if I need to go the o-ring, graphite route.

Thanks for reading.

Jim Pope
Denver, CO
USA

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pendlesteam

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Re: Fine tuning a D10
« Reply #10 on: September 10, 2017, 10:12:38 AM »

Hi Jim
Im afraid that when it all gets hot the blowby will get worse. Might be worth having a look at a little video I made yesterday with a D10 on one of my boilers https://www.youtube.com/watch?v=BzLDGuBCNN8
Might inspire you (not that you need inspiring!)
Nigel
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steamboatmodel

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Re: Fine tuning a D10
« Reply #11 on: September 10, 2017, 04:49:29 PM »


Hi Jim,
Just remember that when you run a steam engine on air, it is not a steam engine, but an air engine and needs Air Tool Oil. One of the fellows in the Toronto Model Engineer Society builds excellent model engine and mounts them on display cases that have a Filter Regulator Lubricator unit in the base. He plugs in the air and can set the speed with the regulator and knows that it is getting lubrication.
Regards,
Gerald.
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jpdenver

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Re: Fine tuning a D10
« Reply #12 on: September 11, 2017, 03:05:10 AM »

Thanks everyone.

So I am moving on to assembling a steam plant.

First, I smoothed out a couple of surfaces, making the shifting
smoother.

https://www.youtube.com/watch?v=B-Ntc8jviAU
This is the result.


Then I got out one of my hulls, which had an undersized twin
and pulled it's plant.

I will have to remove the soleplate and put together some new
mounting rails. But it may work pretty well.

More to come, I will fire it up later this week.

Regards,
Jim Pope
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rhavrane

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Re: Fine tuning a D10
« Reply #13 on: September 11, 2017, 08:32:55 PM »

Bonjour James,
Nice steam plant indeed, I hope the burner will be powerful enough to provide a 2 bars steam to your greedy blue D10.
Do you plan to install a water feed pump later ?
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jpdenver

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Re: Fine tuning a D10
« Reply #14 on: September 11, 2017, 09:12:58 PM »

Raphael,

The Boiler is a Maccsteam - a Full Liter capacity.  The Gas tank will run over an Hour.
At 40 PSI - I get about 35 Min to a tank - without any additional.

If you check the pics above - you will see the side tanks in the boat -
these are for feed-water, just not hooked in yet. I do not have room for
the Stuart pump, so I may have to sneak in an electric one.

I ran the engine on steam - and have some issues:
https://www.youtube.com/watch?v=S3fbX9VyQiA

1.  The Blow-By is very evident.  Time to look at Rings I guess.
2.  I have some sputters on the input and exhaust manifolds - so some gasket goop is called for.
3.  One of my glad nuts is coming loose.   When it runs itself back out, It jams against the piston rod and seizes the engine.
    I know why - I only had a pipe-thread tap and die, so it is tapered.  I think if I wind some teflon tape on it I should tighten up and not effect
   the way the graphite is packed.

Any good ideas are welcome.

Regards to all,
Jim Pope

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jpdenver

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Re: Fine tuning a D10
« Reply #15 on: September 12, 2017, 12:27:16 AM »

To Nigel at Pendlesteam,
About Graphite Cord.

I rummaged in my accumulation of crap, and found two types.

Type 1 -
Is very smooth, but does not have any long strands in it so there is no tensile strength.
Seems to be made for packing. 

Type 2 - is a bit left over from the D10 kit.  Is obviously a string, with graphite.
Lots of tug and pull - tensile strength.

So which to use?

Your thoughts?

Thanks,
Jim



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ooyah/2

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Re: Fine tuning a D10
« Reply #16 on: September 12, 2017, 12:26:30 PM »

To Nigel at Pendlesteam,
About Graphite Cord.

I rummaged in my accumulation of crap, and found two types.

Type 1 -
Is very smooth, but does not have any long strands in it so there is no tensile strength.
Seems to be made for packing. 

Type 2 - is a bit left over from the D10 kit.  Is obviously a string, with graphite.
Lots of tug and pull - tensile strength.

So which to use?

Your thoughts?

Thanks,
Jim


Hi Jim.


Just back from a 3- day trip to Yorkshire.


Use the graphite that came with the D10 kit.


Contrary to the general opinion about "O" rings I use nothing else but them and have done so for the past 20 odd years, fitting them to many engines for friends and club mates they work very well with a long life as long as you make the grooves to the "O" in manufacturers dimensions.
I believe that the Silicone "O" rings are hard to come by in the States  so Stuart's graphite packing will do fine.


Your engine looks great , I would check that the Slide valves are free floating it's the steam pressure that holds them down and you may have marked the faces which could caused the blow back by running the engine dry on air and they may need another  polish.
When you run on steam remember to use a good quality steam oil in the lubricator, the needle valve only needs to be opened a crack to get oil into the cylinders.
I see too many people opening the needle valve too far and using excess oil which isn't required.
  George.


George.
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Re: Fine tuning a D10
« Reply #17 on: September 12, 2017, 09:59:29 PM »

O rings on my PM research #8 engine, runs like a champ. Small length pistons with large O ring groove.
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jpdenver

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Re: Fine tuning a D10
« Reply #18 on: September 13, 2017, 03:14:07 AM »

So it looks like we have two (maybe three) camps.

1.  O-Rings

2.  Graphite

(3) - oil grooves


Well - I tried the oil grooves.  I am willing to bet that my inexperience as a machinist added to the
amount of error in the final alignment.

Result - Well, it ran, but leaked.

So - Since I had some Graphite cord, I decided to try that. 
The graphite cord I had was nominally 1/16 in diameter.
So I removed the pistons, quite a pain - so I think I will work up some type of "wrench" like I saw on another build.
Then I expanded one of the Oil grooves to 1/16 wide and just a little less than that deep.
Then I smashed the cord into it and I will see how that goes, once I remember how it all goes back together.
I could not get just the piston out, so I needed to just about take the whole thing apart.

I guess I will get more practice on timing a Twin Slide valve. - Have to put it back together.

In the event that the graphite does not do the task, I can widen the groove and put in an o-ring.

More to come,

Thanks for the input.

Jim Pope
Denver





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rhavrane

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Re: Fine tuning a D10
« Reply #19 on: September 13, 2017, 07:38:34 AM »

Bonjour James,
You have forgotten the Teflon option (done successfuly on one of my D10)  ok2









 :-))

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ooyah/2

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Re: Fine tuning a D10
« Reply #20 on: September 13, 2017, 12:36:31 PM »

Jim,
If you make a key to unscrew the piston and rod at the same time it saves so much time and the timing need not be altered.


Any time that I make an engine I always make a key to suit to unscrew the piston and rod, I also put some Loctite 603 on the end of the rod that goes into the piston to stop any chance of it unscrewing.


When you make the piston and thread it for the rod when assembling put some Loctite 243 on the screw as it goes into the Cross head slide, also the rod at the Cross head slide make a very small taper with a file to the 1/8" dia rod  which allows you to get the rod thro' the packing gland without disturbing it too much.


George.


Also have a look at this post on the Machining of a D!0 on this forum. 
[size=0px]« [/size][/size][size=0px]Reply #8 on:[/size][/size][size=0px] December 20, 2014, 08:47:29 PM »[/size]


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steamboatmodel

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Re: Fine tuning a D10
« Reply #21 on: September 13, 2017, 03:08:24 PM »


So it looks like we have two (maybe three) camps.

1.  O-Rings

2.  Graphite

(3) - oil grooves


Well - I tried the oil grooves.  I am willing to bet that my inexperience as a machinist added to the
amount of error in the final alignment.

Result - Well, it ran, but leaked.

So - Since I had some Graphite cord, I decided to try that. 
The graphite cord I had was nominally 1/16 in diameter.
So I removed the pistons, quite a pain - so I think I will work up some type of "wrench" like I saw on another build.
Then I expanded one of the Oil grooves to 1/16 wide and just a little less than that deep.
Then I smashed the cord into it and I will see how that goes, once I remember how it all goes back together.
I could not get just the piston out, so I needed to just about take the whole thing apart.

I guess I will get more practice on timing a Twin Slide valve. - Have to put it back together.

In the event that the graphite does not do the task, I can widen the groove and put in an o-ring.

More to come,

Thanks for the input.

Jim Pope
Denver
I would change the first category to Piston Rings, with sub category's of material;
Iron
Teflon
O-rings various materials.
All of which have pro and cons.
I have tried them all except Teflon O-rings. No favorite sometimes it is just what I have available, have even used Teflon plumbers string from the hardware store.
Regards,
Gerald.
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jpdenver

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Re: Fine tuning a D10
« Reply #22 on: September 13, 2017, 03:28:26 PM »

Raphael -
You commented on my youtube post - My definition of "BlowBy" is that the air/steam is escaping without doing it's work.
about 50% or more seems to be just coming out of the exhaust.  I thought it was getting by the piston, but as George said, it
might be that it is getting past the slide valve.

Oh- and I was putting the teflon option in the same category as the silicone.  I saw both as an o-ring.

George -
On your key the little studs look long - do the holes go all the way thru the piston? 
I would not think so - but just checking.

I will look at the slide valve to see if it needs any polishing, and I may adopt your
use of a grub screw as well, this will allow me to adjust the clearances and contact with the
faces.  More experimentation is needed. More knowledge to absorb.

Gerald - Right you are -
The Iron rings are certainly primary - again I was using the term o-ring loosely.
(Loose Lips Sink Ships?)

Anyway - I am attempting Graphite first. 

To All -

I am learning a lot about my sloppiness as a machinist! 
Building a one-off allows one to "make it fit right" but then you find out that the "fit" effects another
part, and you have to go back and fiddle again. 

More to come - I guess - I hope that others may learn from my minor mishaps.
I have no "fear of foolishness" any more -
not with 6 granddaughters wanting to have a "princess tea party" most of the time!

Cheers!,
Jim
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Re: Fine tuning a D10
« Reply #23 on: September 13, 2017, 04:04:20 PM »

Hi Jim,
No the pins don't go thro' the piston, I make them approx 3/16" long and the brass boss that they are fitted into is a clearance fit, with the holes in the piston about 1/8" deep.


Just enough to allow you to unscrew the piston and rod from the Cross head.


Another method is to mill a slot on the piston head to take a screw driver, I prefer the other method described as it doesn't interfere with the top of the piston rod.


I tell you Jim if I had granddaughters a Princes Tea party would take precedence to any machining, count yourself a Blest guy.


George.
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Re: Fine tuning a D10
« Reply #24 on: September 13, 2017, 04:36:39 PM »


Hi Jim,
"I am learning a lot about my sloppiness as a machinist! 
Building a one-off allows one to "make it fit right" but then you find out that the "fit" effects another
part, and you have to go back and fiddle again."
I think that comes under Fudge to fit, Paint to Match" category, I would hate to admit how many times we used that when I was working due to sloppy tolerances. Enjoy the Tea Parties, I am still waiting for my offspring to provide Grandchildren.
Regards,
Gerald.
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