Blow back problem with some Mamod SL/MSS loco meths burners

[Chris Cairns]

We have briefly touched on this subject recently, so whilst I'm building an MSS loco kit I took the opportunity to take some photos to try and illustrate this potential problem.



The Mamod SL/MSS locos are supplied with a solid fuel burner tray. To allow this to slide into the chassis the rear face of the combustion chamber has a wing bent horizontally at 90 degrees. When the burner tray is fitted the vertical plate on the back of the tray covers that gap between the chassis and the combustion chamber so no chance of any flames reaching the cab.



I recently obtained a copy of an article from 1981 which proved that the solid fuel would actually perform better than liquid meths, and concluded that the problem with the SL1 lies with the design of the burner tray and the combustion chamber. As this would mean a major redesign of the SL1 loco the after market introduced replacement meths burners instead. The design which has lasted until now is the 3 wick burner available commercially from Dream Steam & Chasteam. As I understand it these are a copy of the original 3 wick burner produced by Mike Chaney (unfortunately I've never seen one of these for a comparision), and were produced by IP Eng (out of which Dream Steam developed) and latterly PPS Steam Models as well.

When fitted to the Mamod SL/MSS loco the rear vertical plate on this burner mates with the horizontal face of the combustion chamber. So no risk of a blow back from the burner into the cab.



This is an IP Eng burner fitted to the MSS loco.

The Chasteam burner is slightly different to the IP Eng/PPS/Dream Steam burners. It has a block fitted at the rear of the burner so this burner mounts lower than the other burners (thus it is less efficient). The vertical plates fitted forward of the fuel tank are also smaller.


Chasteam burner on left, IP Eng burner on right.

I've modified my Chasteam burner by removing that block at the rear so that the burner tubes are the same distance from the boiler as the other burners.



Even with this modification those vertical plates do not provide enough protection to the cab so a blow back with these burners is possible.


My modified Chasteam burner fitted to the MSS loco - you can see daylight through the gaps between the chassis and the combustion chamber.

I'm not sure why these burners are fitted with 2 vertical plates but the forward one does not mate up with the curved surface of the boiler.



Whilst future burners could be modified to correct this problem there is a solution to adapt current burners.


(I assume the cut-out in the top curved part is for a regulator steam pipe to/from the cab)

These chassis guides were provided with the MGM Engineering meths burners. Whilst not a perfect fit they are designed to slide between the chassis frames to mate up with the boiler surface.



The combustion chamber fitted to the IP Jane/PPS Janet is a different design. With no solid fuel burner tray to fit the rear face of the combustion chamber is vertical and fits between the chassis frames.



When the burner is fitted to the IP Jane (PPS Janet) the vertical plates on these burners are forward of the rear face of the combustion chamber.



So if you want to reduce your risk of melted plastic sight 'glass' when using a meths burner with a Mamod SL/MSS combustion chamber and standard boiler check that you have no gap between the chassis and combustion chamber. Otherwise a protective plate like the MGM Engineering one above could seal that gap to prevent a blow back.

Chris Cairns.

[Spule 4]

Good info as always Chris.

There was some discussion years ago regarding flashback on burners.

The Sidestreet Bannerworks burner did not have any plates on the fuel suppy to the burner tubes, but its mounting bracket was a bit of brass angle that closed the hole and held up the burner.

http://www.sidestreetbannerworks.com/locos/loco36.html

Other features included the tangs on the back of the tank that held on at the screws from the frames to the rear drag beam, the overflow on the tank and the rearward filler neck.

With this design, any addition of plates (going by memory) was to prevent the actual flashback of fuel "wicking" down the outside of the tube. One suggested solution was even soldering a brass washer on the tube to serve as a stop of any wicking down the tube.

The two plates? Proably (guess) A) prevent the wicking and B) serve as a flashback and thermal shield, but lacking full protection as you point out.

[Chris Cairns]

Garrett,

Where is the overflow on the Sidestreet Bannerworks burner - just forward of the mounting bracket stud?

The wicking you mention is now dealt with by using the ceramic wick material. After some use this tends to seal around the top of the burner tubes which reduces any spill of meths when a loco derails and turns on its side. Certainly works very well in my Bowman locos which can get away from you (no regulators).

This ceramic wick material can be expensive from traders but I've got a supply of wood burning stove rope which is basically the same.

Did the Shirley meths burner come with any protecting plates?

Chris Cairns.

[Spule 4]

Chris et al-

The overflow is just before the rear drag beam on the opposite side at the bottom of the side. Imagine a soldered tube inside the tank shaped like a letter "J", with the top near the top of the tank, and the bottom out the rear side.

So when you fill it up, when it overflows, it shoots out the back-rear.

My Shirley burner came with nothing but the burner, for about $8 US, I can get a UK magainze from 1980-ish that has a review on the burner.

I have, however, modified and raised my tubes with some spent .22 250 shells....