MaccSteam boiler tests with Graham engines "Scotch yoke" SC1A, and "Twin" TVR1A.

[Brooks]

I've posted some bench test results over on rcgroups.com:

http://www.rcgroups.com/forums/showthread.php?t=1216529

[kiwimodeller]

Interesting work. What length is the Maccsteam boiler? I have a locally made 6" x 3" horizontal boiler with a flue that has a 90 degree bend to exit through the top of the boiler drum rather than going out the end. This is driving a Graham VR1A single cylinder engine in a 3' long river launch (picture attached). I am using a 1" diameter ceramic burner with a Number 5 jet and this gives me at least 25 mins of run time. I believe that running on the bench with no load uses more steam than running under load on the water. I have experimented a bit with different primary and secondary air holes and jet sizes in the burner. A number 8 jet and larger air holes does give more heat but produces more steam than I need and the relief valve (set at 40psi) goes off during the run even with the flame turned down a little but it does show that the boiler is capable of producing plenty of steam and I intend to try the same size boiler when I build a TVR1A. I do not concern myself too much about the water level dropping below the top of the flue. I have cross tubes in the vertical part of the flue and they survive being above the water level half the time. I do not believe the burner produces enough heat to melt silver solder as long as the boiler is not completely dry. Maccsteam vertical boilers seem to be built the same way as the horizontal ones but with the 90 degree bend in the flue at the bottom end and if they have cross tubes most of the way up then some of these must be out of the water a lot of the time. I intend to have my boiler man build me a vertical in this style sometime in the future so will post the results when it is going. Hope this gets some others sharing their experiences. Cheers, Ian.

[Brooks]

Hi Kiwimodeler, thanks for the jet data. You have a nice setup on your launch.

The Maccsteam site says the 2 1/2" dia. horizontal marine boiler is 5" long, 6.5" with the burner. The 3 1/2" dia. boiler dimensions are listed as 6" and 7.5". His boilers, like yours, have the exhaust stack running out the top of the boiler, not the end - there is a copper plate soldered over the far end of the flue.

http://www.maccsteam.com/Horizontal_Marine_boilers/Marine_boilers.html

I, too, have wondered about the danger of melting solder holding dryed-out crosstubes that are always present in a vertical boiler; or, if not the cross tubes, the uppermost flue joint..... and how this relates to the dictum to always keep the flue and crosstubes wet in a horizontal boiler. My only thought on the difference between vertical and horizontal flue boilers is that at least the part of the vertical flue next to hottest part of the fire is always bathed in water, right up until you run the boiler dry (for vertical boilers with the burner located at the bottom of the boiler, not the case with Mike's vertical boilers, see his photos). Whereas, the hottest part of the horizontal flue is not protected once the water drops below the level of the flue on a horizontal boiler. I endeavour to keep the horizontal flue always covered, but don't worry about a vertical flue drying out at the upper end.

I notice on Maccsteam's vertical boilers that the water gauge stops short of the  the horizontal, burner-entry flue, though (see his photos to clarify). This implies that Mike does not want one running the water too low in his vertical boilers. It appears he wants more water protection of his burner flue in his vertical boilers than the flue in his horizontal boilers. On his  horizontal boilers, the water gauge ends just above the flue; thus, as long as you can see water (provided the gauge is accurately recording), you have horizontal flue protection.

I suspect that Mike designed his vertical flue boiler burner location to keep the overall boiler height lower; he saves 1.5" that way. It's always nice to keep the c.g. low.