Newbie

[gjmcleod]

Further to my intro....probably in wrong forum....

I have a Saito V4 steam engine desperately in need of new "O" rings (boiler and other fittings need new seals too).

Any ideas for supply of these rings?

Graeme

[gjmcleod]

I forgot

I've a partly completed triple expansion engine model, VERY much top-heavy. Have these triples ever been used to drive paddles, or were they confined to (hush my mouth) screws?
Graeme

[derekwarner_decoy]

Hi PD's ....& welcome Graeme.....

As nice as the beautiful Saito V4 piston valve engine is, she would need a substantial speed reducer to get from say 4000 PRM down to a model paddler shaft axis of approx. 150 RPM

I think Saito ceased manufacture of these V4's in the early 90's...[so it is a valuable engine  in more ways than one]

Three cylinder [triple expansion] steam engines were used in full sized older paddlers, however specifically designed as horizontal engines with longer stroke to bore ratios to reduce the crankshaft speed & maximise torque......I am not aware of any triple expansion verticals adapted for marine paddle work

My 20 year & going build has a Saito horizontal twin.....

With respect to replacement O-rings, you will need to size them accurately, plus also measure the bore [* see note below] and the cavity ID plus height on the pistons and compare these dimensions, as the outoing O-rings will have deformed and stretched during use

Another point is the replacement O-rings must be Viton elastomer or silicone.....the latter is more expensive and less readily available.........In Australia we use the term Viton, in Europe and the USA, the same elastomer is commonly referred to as FPM
Nitrile O-rings are only suitable for temperatures bordering 100 degrees C....the steam form a model boiler at 3 Bar is approximately 150 degrees C

O rings by designation are measured by the ID x the cross section.......if you are able to accurately measure the dimensions as noted [vernier caliper or digital veriners will suffice].......the ID of the piston seal cavity x the height of that cavity, plus the OD of the piston, as the flats on the caliper will provide a false reading when measuring the bore....the actual selection of the o-ring also considers the required compression crush .........

Confirm these dimension's & I will relate these back to standard o-ring codings [you will see the FPM designation as this is a European publication] that you can obtain from any bearing supply company, or a hydraulic supply co...............

Below are images of the o-ring publication ...followed by my Saito horizontal paddle engine......

Derek 

[steamboatmodel]

Just a word of caution when useîng Vinton O rings, if exposed to high temperatures it degrades into hydrofluoric acid. I am talking about much higher temperatures then what we operate at, but if you had   a bad fire and found the O ring had turned sticky brown black and do not touch it with bare skin.
Gerald.

[derekwarner_decoy]

Graeme......with the V4 being taken from production many years ago, I have never seen the engine personally, however just Google Saito V4 & you can spend hours watching them in operation

Saito engines are universally known for the ability of rotate on very low steam or air pressures

I have read a number of years ago where a second hand Saito engine was purchased from ebay and assumed as needing piston seals as the force required to rotate the crankshaft flywheel was considered LOW

Have you stripped the engine?....are the piston seals actually O-rings or could they be square section Teflon rings?

Have you done a piston seal bypass test by holding the output shaft then applying steam/air?...this test should also be performed in both directions and at TDC, mid stroke and again at BDC...again the tests should be conducted with low pressure [say 0.5 Bar] as a reference basis then at the boiler relief valve pressure.........

If you check, most Saito WEB sites are vague in their recommended WP, an American translation talks about maximum power being archived at 2 Bar.......yet many Saito engines appear to run happily at 3 Bar......

Both o-ring sealing and Teflon square section ring sealing is accomplished as the seal elements are pressure energised & hence expand with pressure to create the sealing function between the piston seal cavity OD and the cylinder bore

O-rings are readily available, Teflon square section rings are not commercially available without great expense and also the need for expansion and re-sizing taper tools

 Derek