5" Hunslet Progress

[ron]

Here is a photo of the work so far on the frames and running gear


and a picture of the cylinder casting beside Simplex for size comparison


and the boiler courtesy of Western Steam

[baggo]

Good progress Ron, keep the pics coming

John

[jgb7573]

Nice one Ron. And if it pulls anything like the one I have (built by a friend), you'll be very pleased with it.

Thanks for the pics.

[Shawki Shlemon]

I like the neat silver soldering particularly the stays . Well done .

[AndrewP]

Looking good Ron, that chassis is a huge lump isn't it?
I notice you have done the cutouts for exhaust ports, are you not going with the balanced slide valves or just hedging your bets at this stage

Andy

[ron]

Hi Andy
I don't really know what balanced valves are and I'm not really any the wiser after studying the drawing, I'll cross that bridge when I come to it, my only experience is of standard slide valves in Simplex and a couple of Stuart Turner engines which seem to work fine, but if the balanced valves are better then I'll go for them.
Ron

[baggo]

Hi Ron,

I'm trying to work out a design to convert my Simplex cylinders to balanced valves. The idea is to isolate part of the back of the slide valve from the steam chest pressure so the force pressing the valve onto the port face is greatly reduced. The load on the valve gear and wear of the port face is thus reduced as well.

In the Hunslet, the spring loaded 'balance piston' does this job but there other ways. It seems normal to make the area of the balance piston etc. about 90% of the area of the exhaust cavity in the valve. This reduces the pressure on the valve by 90%, the remaining 10% makes sure the valve still seats properly at all times, although it can be lifted at the end of the stroke if the compression is high.

Also in the Hunslet, the exhaust exits through the valve itself rather than through the normal exhaust port in the cylinder block giving a freer escape route for the exhaust steam although I think that is probably of secondary importance.

John

[AndrewP]

Are they better? no idea, haven't got that far and you'll be there long before me.
The Hunslet balanced slide valve works by having a spring loaded piston on the back of the normal slide valve, said piston seals to the steam chest cover which has a port in it for the exhaust steam which therefore goes through the valve rather than the normal convoluted route.
I have a copy set of the build articles from Reeves if they would be of use, the photo reproduction is useless but the text still works. I've got the originals if I ever get a round tuit

Cheers, Andy

[ron]

Hi Andy and John
Thanks for that, it's a lot clearer now, I may as well make it as per the drawings, the balanced valve does seem like a better method. I've got the original articles, they aren't really all that great but better than nothing.
Ron

[Steamgramps]

You will get a lot of fun out of running your Hunslet as I have from Terry B Aspin's model of Holy War. Keep up the good work.

Steamgramps

[havoc]

Baggo posted a scan of the drawing of the balanced valves here: modeleng.proboards.com/index.cgi?board=general&action=display&thread=4660

[ron]

Here's a photo of the cylinder steam passages getting drilled and milled, luckily I had a long series 4mm carbide mill or it would have been a bit of a struggle, the 8 ports are 3/16"X 5/16" and 1.25" long, I managed to make them slightly larger than the design as they look like a bit of a bottleneck compared to size of the steam inlet pipe etc.
That's both cylinders done and just the slide valve part of the balance valve to make to complete them.
Ron