|
Post by chris vine on Dec 8, 2023 17:07:48 GMT
A cunning plan, but I still wonder if there isn't something like insufficient gap or a bottom corner in a piston groove which is holding them out a little. Some experimenting and observation is called for.
IE, can a straight edge push the rings right down into the groove etc..
C
|
|
|
Post by jinks82 on Dec 21, 2023 9:52:44 GMT
I make these and other piston rings for a living. Sounds to me like the bore size you gave to Alan may not of been so accurate. If they are finished to a diameter even a thou over your actual bore size, the rings will be too compressed meaning there is less than no ring gap, causing excess wall pressure. Clupet rings are difficult to gap if your not practised in manipulating them. I usually stress the importance of giving a accurate bore diameters for this very reason. A 0.001" difference in bore is equal to over 0.003" at the ring gap, or a difference of pie. I usually machine the final diameter of rings to give a small ring gap, depending on how confident I am of the customers measurement! Hi Tim, would you be interested in making new rings for me were I to provide you with accurate details of my pistons and bore? Thanks
|
|
weary
Part of the e-furniture
Posts: 290
|
Post by weary on Dec 21, 2023 19:16:54 GMT
Tim made some clupet rings for me ( Rufford Steam Works) for a 5" gauge steam loco and they are excellent. Can recommend as a satisfied customer (& with no other link whatsoever, commercial or otherwise). Phil.
|
|
|
Post by Oily Rag on Dec 22, 2023 21:18:35 GMT
Interesting and thank you Chris for this video. I am sure to give this ago in the years to come with the Foden lorry and 5" build
|
|
|
Post by jinks82 on Jan 22, 2024 10:40:11 GMT
I am having trouble contacting Rufford Steam Works. I've left messages and sent an enquiry but to no avail Does anyone know if this is still a going concern?
|
|
weary
Part of the e-furniture
Posts: 290
|
Post by weary on Jan 22, 2024 19:12:06 GMT
timjenkins31 was last on this forum 19 hours ago at time of writing; i.e. 11 hours prior to your last posting. Maybe PM him on here as well as hoping that he spots this thread and responds directly to you.
Phil
|
|
|
Post by jinks82 on Feb 8, 2024 10:28:23 GMT
What do you chaps think about using PTFE for piston rings?
|
|
stevep
Elder Statesman
Posts: 1,070
|
Post by stevep on Feb 8, 2024 16:57:13 GMT
I've had them for years on my Rob Roy.
|
|
JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,909
|
Post by JonL on Feb 8, 2024 19:53:47 GMT
I've used Fluroscint after being kindly given some by a generous member here, fantastic stuff. Lower rate of expansion than PTFE so still seals well when cold.
|
|
|
Post by Rex Hanman on Feb 9, 2024 8:20:37 GMT
I've had them for years on my Rob Roy. Ditto
|
|
|
Post by Boadicea on Feb 9, 2024 14:07:29 GMT
What do you chaps think about using PTFE for piston rings? Are we talking of making rings in PTFE or using square profile PTFE gland material?
|
|
stevep
Elder Statesman
Posts: 1,070
|
Post by stevep on Feb 10, 2024 10:21:42 GMT
I made my rings out of PTFE. Turned them to size, inside (with clearance) and outside (smooth fit), then parted off a ring. Split it by cutting at an angle with a scalpel.
|
|
|
Post by Rex Hanman on Feb 10, 2024 15:09:11 GMT
I made my rings out of PTFE. Turned them to size, inside (with clearance) and outside (smooth fit), then parted off a ring. Split it by cutting at an angle with a scalpel. Ditto again.
|
|
|
Post by jinks82 on Feb 15, 2024 10:59:30 GMT
Thanks. I have purchased a 50mm round bar of PTFE. I wonder if anyone could give me some advice on clearances? Bore is 1.685" and the piston groove is 1.532". The current groove width is 0.163". These groove dims were dictated by the clupet manufacturers. I'd be very grateful for any advice
|
|
oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
|
Post by oldnorton on Feb 15, 2024 15:12:33 GMT
The PTFE rings are best sitting on a pair of fine o-rings; the o-rings help maintain a slight pressure on the PTFE (or just one o-ring if the PTFE ring is thin enough). There have been published designs, or work out your dimensions using 1mm or 1.5mm diameter. o-rings. About 3-6 thou of radial compression for the o-rings and allow 2 thou free at the side. Those are my numbers and others are welcome to give their versions. There is an argument that if you have o-rings it is better to have no side clearance as once the steam gets in and underneath there is substantial wall pressure - this is quickly proven by an air test when the piston can grip firmly in the bore. Without the o-rings it will be essential to have ring side clearance so that the steam (or air) can push the rings out and effect a seal.
There is virgin PTFE, and filled versions with 25% glass or 25% carbon (graphite). Some think the filled versions do not suffer the sudden expansion of PTFE between 15-25 degC, but the reduction is only in proportion to the inert fill. Virgin PTFE will work fine, but the filled versions are more dimensionally stable and better to machine accurately. The graphite filled is preferred. The thermal expansion of PTFE is not an issue for split rings where the gap is adequate.
Norm
|
|
|
Post by jinks82 on Feb 16, 2024 9:41:48 GMT
Many thanks Norm. Carbon filled is way too expensive for me due to minimum order and postage costs. Is there some information regarding piston ring sizing? I.e. if my bore is 1.687", my current piston groove dia is 1.532" and groove width is 0.163", how do I calculate the PTFE ring dims? Hopefully I may see you at the Northampton track one day!
|
|