Piston rings or graphite packing ?

[david newman 9Participant @davidnewman9]

I have recently completed a Stuart number 9 and I fitted the piston rings supplied

the engine runs superbly except I can hear a slight knock very slight, this appears to be coming from the piston and rings. I fitted the rings to what I considered a good slide fit in the groove, well I set up a DTI on the end of the piston rod and have a 2 thou movement between rings and piston groove, found this by gently rocking the flywheel ( no play anywhere else). It’s bugging me because with my ear to the engine I can hear this slight tapping noise coming from within the cylinder, thinking about taking the rings out and using graphite packing instead. Am I being super critical ??? David

Edited By david newman 9 on 25/10/2011 19:40:21

[david newman 9Participant @davidnewman9]

[Sub MandrelParticipant @submandrel]

Probably

 

Well, you did ask…

 

Neil

[Ramon WilsonParticipant @ramonwilson3]

David,

 

I haven’t fitted piston rings to any stationary steam engine made so far but have always used PTFE impregnated yarn. This comes in square section, the size I have is 1/8. I ran my twin Victoria fitted with this for many years on steam (dried) without any problems -not doing any work of course just turning over for display purposes. The engine had good compression but could be turned over easily and smoothly by hand. Likewise the Double Diagonal. Only run on air the seal on this is such that if I close the inlet valve and turn the engine over by hand it will compress the air within the cylinders sufficient to turn itself about 3 revs.

 

There is very little drag on the piston using this material which makes for some easy slow running. I think I bought mine from Reeves many years ago – I guess they will still have it

 

Depends on what you want to do with the engine of course but if it is just to tick over on the bench – as well as a good fast run too of course – yarn will the job nicely

 

Regards – Ramon

[WolfieParticipant @wolfie]

I’m planning to use an O ring in mine, report later.

 

[Ian S CParticipant @iansc]

With the piston rings think .002″ is a bit much clearance, but should be OK. I woyuld use Teflon tape instead of graphited hemp, it will do better than an O-ring and easyer to fit. Ian S C Do’nt know where the italics came from

[Ramon WilsonParticipant @ramonwilson3]

Hi David,

I don’t know if you have managed to improve your set up on your Number Nine or whether any suggestions were useful, however I thought you might like to see the piston made for the Waller engine today which is fitted with PTFE loaded yarn.

 

 

It is very easy to fit – The piston is 0.05mm down on diameter and the groove is made just slightly wider than the stock material to allow it to spread as it becomes compressed in the bore with the depth about .05 less than the nominal thickness.

I tapered the top of the bore very slightly with a hand scraper to help it’s entry and pushed it in using the drill press to apply very slight up and down ‘bouncing’ movements to get it to enter. As you can see the material was cut at about a 30 degree angle such that it was in the groove rather than across it.

 

It has provided a good seal but without a great deal of drag – I can move the piston up and down freely enough by hand but there is very good compression.

Don’t be too put off by the apparent grubiness – it begins quite white but soon picks up the slightest dirt on your hands!

 

I see Reeves do list  it on their website but it’s a bit dearer than when I bought mine but then again what isn’t

 

Hope this is useful to you

 

Regards – Ramon

 

 

 

Edited By Ramon Wilson on 01/11/2011 22:38:21

[charles oliverParticipant @charlesoliver21638]

Does anyone know a source of data on small o-rings and the sizes of their grooves? This is for cylinders 11mm diameter.

Thankyou

Harry

[mgjParticipant @mgj]

Model Engineers Hand book. Tubal Cain. Absolutely all the info on Imperial and Metric o rings you will ever need.

 

And on piston rings!

 

And on just about any other bit of useful Workshop Data an ME will need.

[Brian JohnParticipant @brianjohn93961]

1. Is it possible to make your own piston rings ?

2. How necessary are they ? What if you did not use any rings or Teflon packing at all ?

[JasonBModerator @jasonb]

1. Yes done it quite a few times

2. For a display engine thats just ticking over it will more than likely work OK without rings, maybe a bit of wasted air/steam so not as efficient. Once you start putting a load on the engine and making it work then you start to get more air/steam getting past the rings and also have to start thinking about rates of expansion of the various metals as the rings take up some of the slack. For example when cold an aluminium piston in a CI liner will nee a few thou clearance per inch dia but once its upto running temp there will be littel gap as the aluminium will expand more than teh iron.

J

[Brian JohnParticipant @brianjohn93961]

What do you make piston rings out of ?

[JasonBModerator @jasonb]

Usually cast iron bar though some people use teflon or bronze for use on steam engines. For the smaller engines you are working with at the moment I would stay with Graphite yarn or the PTFE equivalent as they are a bit more forgiving of fit.

 

"O" rings are another option, the Minnie in my avitar uses Silicon piston rings and also has O rings as gland packing.

 

J

Edited By JasonB on 11/09/2014 18:29:51

[Mark P.Participant @markp]

Silicone "O" rings every time.

Mark P.

[John BaguleyParticipant @johnbaguley78655]

For steam use Viton seems to be the prefered material for O rings. I gave up on O rings for piston seals a long time ago and now use rings made from PTFE for gunmetal cylinders.

John

[Ian S CParticipant @iansc]

For PTFE rings you can plat together Teflon plumbers tape, seems to work ok, and it holds it together. I used the plumbers tape for the glands on the Stuart Turner S9, The engine has only run on air so I don't know how it goes on steam, but should be just as good.

Ian S C

[Howard LewisParticipant @howardlewis46836]

Another source of data on O rings and the grooves for them should be Simrit, who manufacture O rings of all types and sizes. Have a look at their website to see where it leads you.

Howard

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