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Post by johnharkness on Apr 5, 2006 19:37:15 GMT
Is there any advantage in using 'o' rings instead of packing on pistons any suggestions please.
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Post by havoc on Apr 5, 2006 20:52:26 GMT
I started with O-rings and went to teflon thread packing. The problem I had with O-rings is that if everything isn't dimentionaly correct, then you will have more friction because the ring tries to roll. With packing, you add a bit or take off a bit.
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JohnP
Hi-poster
Posts: 186
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Post by JohnP on Apr 5, 2006 20:53:58 GMT
From what I can gather, the surface finish of the bores must be good for o-rings not to wear out quickly. Having tried (and failed) to pack pistons, I've been looking at this and I'm wondering about a proper industrial PTFE seal, possibly with an o-ring underneath to provide some spring. I need to do some more digging on this though.
JohnP
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SteveW
Elder Statesman
Posts: 1,463
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Post by SteveW on Apr 5, 2006 21:24:37 GMT
Guys,
Re: "more friction because the ring tries to roll"
It is essential that the 'O' ring does roll, the groove must be a bit wider than the ring to allow this.
There was a long thread here on using these things a while back. I quoted a web site that provided a load of application data on the various parameters necessary.
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Post by chameleonrob on Apr 6, 2006 8:22:21 GMT
two other things to remember. pick your O ring material carefully, the most common type nitrile which is only good upto about 100oC and steam gets hotter the higher the pressure is, at 100psi water boils at 170oC. The other thing is to remember that at some point they will need replacing and with packing you don't have to take the piston rod off the crosshead to remove and fit the seals. I'm writing from experiance here as I've been spending quite some time recently repairing a friends loco that wasn't designed to be maintainance friendly, it took 2 1/2 hours to remove the grate.
Rob
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Post by burnettsj on Apr 6, 2006 10:04:23 GMT
For piston rod glands- cut the O ring at 45 degrees - to fit over the piston rod, the gland will then hold the ring together - and is steam tight - will easily last 2000+ miles.
Admittedly this is a "cheat" and not how O rings are designed - but it works.
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Post by ron on Apr 6, 2006 10:08:59 GMT
Hi
I've turned square O rings from PTFE and slit them at 45 degs to make piston rings, they need to be dimensionally quite accurate as they seem to swell slightly in use and jam if not spot on.
Ron
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Post by chris vine on Apr 6, 2006 14:22:58 GMT
Hi,
What are your cylinders made of and what size?
If you are just considering pistons and the cylinders are cast iron, it is difficult to beat iron piston rings. They wear in rather than wear out.
A lot of people seem to think they will rust into the bores if left for a day or so. In my experience, as long as the cylinder is lubricated, they do not tend to stick at all. Even after leaving all winter the locomotive rolls freely.
What do other people find?
Chris.
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Post by havoc on Apr 6, 2006 17:08:43 GMT
Can you explain a bit further? I tried this, but it leaked like mad. I made them to have a bit of play with respect to the piston and a bit oversize with respect to the bore.
Could this be done in gauge 1?
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Post by chris vine on Apr 7, 2006 1:19:32 GMT
Hi Paul, I think cast iron rings in gauge 1 is probably a bit too small. Also, usually gauge 1 cylinders are made of bronze / gunmetal......
Chris
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Post by havoc on Apr 7, 2006 17:00:55 GMT
Who said everything has to be usual?  |
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Post by steammadman on Apr 7, 2006 21:23:40 GMT
I have tried " o" rings, graphite string,and ptfe, with brass based cylinders and i think i favour
"ptfe", if wound in very tight , providing you get good lubrication they seem to last for ages,
for me anyhow.
For cast iron i find that all the above three types of packing "tear" far too easily,and always seem to let you down at the most in-opertune moment.
So for cast iron cylinders , i say "rings only" , as already stated they wear in rather than wear
out. So good and well fitting rings will last a lifetime with good lubrication.
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Post by steamjohn248 on Apr 11, 2006 19:15:09 GMT
I agree with steamadman, cast iron really works best with proper rings.
Clupet Piston Ring and Gauge Co will make them to order in any size and send them with info on groove clearance etc. Tel / Fax 01900 818361. Usual disclaimer except as a satified customer
Steamjohn
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Post by burnettsj on Apr 12, 2006 8:51:15 GMT
I agree with steamadman, cast iron really works best with proper rings. Clupet Piston Ring and Gauge Co will make them to order in any size and send them with info on groove clearance etc. Tel / Fax 01900 818361. Usual disclaimer except as a satified customer Steamjohn Their Clupet rings are superb (double piston ring - like a key ring in form). I have moved a 7.25 engine with approx 0 psi on the clock, which has Clupets of both valves and piston under its own steam! (again usual disclaimer) |
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dscott
Elder Statesman
Posts: 2,440
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Post by dscott on Apr 13, 2006 10:02:29 GMT
Dear All,
On my Gemma, and again on my Terrier, I used Gunmetal cylinders and O rings, I dont remember how long I spent polishing the bores, (boring job) but worth every moment as both engines run very freely and have had no maintainance for about 20 years. Iwas also a lot younger then and not married.
PS. I must finish the terrier water tanks one day which are of brass with a steel cover for the paint. Just by luck, precision paints are bringing out the proper transfers next year so at last Earlswood will have a proper name.
David Scott.
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