Mamod Ceramic Gas Burner

Chris Cairns · Post by **Chris Cairns** » Mon Mar 04, 2013 8:03 pm

I'm not going to remove my Mark II burner again (trying to paint over the aluminium rivets) but I have a smaller Mamod burner that is mounted in a scuttle for the traction engine/steam roller. As the air/gas pipe goes into the body of the burner it does have a slight venturi going into a smaller diameter tube which seems to have a further restriction at the far end.

In the circular ceramic burner I got from RWM for my De Winton prototype the air/gas tube is straight to the edge of the burner box where there is a piece of stainless steel mesh across the mouth of the tube. There does not appear to be anything else under the ceramic (torch shines through to the bottom) and this burner glowed very red in my recent trials.

In the small ceramic burner for an internal flue Cheddar Models boiler the air/gas tube is straight but extends almost to the far side of the burner. Again there does not appear to be anything under the ceramic, and this ceramic has much larger holes than the other 2 above.

I do have a Bix burner but that requires dismantling my De Winton which I do not wish to do until I'm ready for that project to start again.

Hope this helps your enquiry.

Chris Cairns.

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Mon Mar 04, 2013 8:23 pm

Thanks for the info Chris. Like you, I'm put off taking the burner out of the Mk11 unless I have to, its too much trouble and anyway it seems to work well as it is.

However I am tempted to have a tinker with my Brunel as currently turning the gas up beyond a tiny amount results in the flame lifting off the ceramic and then going out only to re-ignited with a bang a second or so later. Not really an issue but it means you have no fine control of the burner. Could this be caused by a venturi effect speeding up the gas/air mix?

Perhaps I'll wait a couple of weeks first though and then bother Mamod again and ask them about the Brunel burner and if it too has a venturi. I don't want to distract them now from anything other than the Thomas Telford.

At the same time I'll try to get some more details of what exactly they've enlarged in the burner. You never know, it might simply be a case of drilling a larger hole of a specified size.

Mamod are going to be at The Telford Garden railway Market this coming Saturday which I would normally attend but unfortunately I'll be in London visiting family. If anybody else is going perhaps they could do a bit of asking.

Mike

Chris Cairns · Post by **Chris Cairns** » Thu Mar 07, 2013 4:04 pm

Mike,

Here is the ceramic burner air/gas tube on my Diamond Jubilee Saddle tank loco.

You can see the venturi effect at the bottom of the tube. Previous owner had an interesting leak on this burner which I'll reveal in a new Diamond Jubilee Topic soon.

Chris Cairns.

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Thu Mar 07, 2013 6:13 pm

I've been doing a bit of reading up on venturi gas burners and all the information I've found so far points to them having a design something like the diagram below:

As you can see, the venturi accelerates the gas which mixes with air at the other side. The Mamod burner mixes the air and gas before the venturi so all it does is accelerate the whole mixture for no purpose as far as I can tell.

Mike

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Mon Mar 11, 2013 4:50 pm

I spoke with Peter Johnson at Mamod today. He says they are drilling out the venturi in the ceramic burner with a 6mm drill. You have to be very careful as behind it is part of the ceramic of the burner.

Its Peter's view that the venturi is speeding up the air and gas to such an extent that they don't have time to mix properly. By removing the venturi the gases are slowed down, mix correctly, and result in more efficient combustion.

He also said the Brunel burner doesn't have a venturi.

Mike

Chris Cairns · Post by **Chris Cairns** » Mon Mar 11, 2013 6:49 pm

Mike, Thank You for the continued interaction with Mamod.

So who is going to be the first one to try drilling out their gas burner venturi? Due to other projects backing up this will be a low priority for me at present.

What I hate with the Mark I, Mark II & Saddle Tank is the burner has had to be mounted using 8 washers due to the chassis spacing. And I've yet to find an effective method of keeping those washers attached to the burner (Loctite gives up after the burner heats up, and there is very little metal on the back mounts to get an effective solder joint).

Chris Cairns.

Lner fan Sam · Post by **Lner fan Sam** » Mon Mar 11, 2013 7:21 pm

Would solder paste do you any good chris.

steamie1 · Post by **steamie1** » Mon Mar 11, 2013 8:58 pm

Reading with interest I today, looked hard, at my Mk2 burner.

Turned up too much and an erratic flame starts leaping about. It assures me that rich is erratic. The setting which causes erratic burn, is so much more than is healthy, but with such a course thread I can see the novice could make this mistake.

It is more than powerful enough perhaps overkill performance wise. I think set low to medium, the air/gas ratio is right for the MK2. I think william was too rich with less slots and somehow looses steam causing customers to turn it up further making things worse. I'll shut up now as I have no info to add only Mk2 ratios are right just keep em set on the low side. I have run mine in 40mph gusts, all was as good as it could be, the cold air providing the facility to turn the gas up a tad without the above problems as the air was denser. I wonder on a hot thin air day if the gas will have to be set to low, maybe I'm using my peanut brain too much, I'll read with interest what you guys come up with.

Chris Cairns · Post by **Chris Cairns** » Tue Mar 12, 2013 12:29 pm

Lloyd,

The problem with the Mamod ceramic burners is that they do not burn as well as other manufacturer ceramic burners do.

They should have a nice strong pattern of blue cones just on top of the ceramic, and the ceramic should glow a nice radiant red.

If the theory about the wrong use of a venturi is correct then the gas/air mix is not mixing properly and actually burning mostly above the ceramic - hence the requirement for large air slots and air holes in the combustion chamber side walls.

The original Mamod SL/MSS/IP Jane/PPS or RWM Janet only have two small air holes in the side of the chassis frames with the combustion chamber resting over the side of those chassis frames, yet the Cheddar Models, PPS Steam & Bix ceramic burners are very effective.

I'm sure we will see an improvement in the erratic flames of a Mamod burner if that venturi is opened out.

But my Mamods have been getting too much attention in my 'workshop' recently and other projects are screaming out to be finished first.

Chris Cairns.

Chris Cairns · Post by **Chris Cairns** » Fri Mar 15, 2013 6:54 pm

Having put my Mark II & Saddle Tank back into temporary storage, my William II was now sat on its own in my workshop.

Given that the burner is easier to get in & out of the chassis (no extra washers for spacing), I decided to try drilling out that venturi.

The venturi is 4mm wide so using a mini vice and a power drill I opened the venturi out to 6mm, but not to its full depth. Initially I had problems lighting the burner but that was due to some swarf being stuck below the ceramic material. Having blown/shaken that swarf out the burner lit up OK.

Pressure was raised quicker but whilst running around my test loop the burner was suffering from the occasional pop-back to the jet.

So today I continued drilling out that venturi to the end of the tube without hitting the ceramic material behind. The burner now works great with no pop-backs.

Whilst the William II still needs to stop during a run to raise pressure again, it now comes back quicker and by slowing opening the regulator more as it slows down I have increased the time between stops for more steam pressure. A candidate for a proper lubricator with a bigger capacity. It also no longer suffers from those sudden speed bursts!.

Chris Cairns.

Chris Cairns · Post by **Chris Cairns** » Sat Mar 16, 2013 12:29 am

Another result.

I decided to take my William out of storage (last ran about 4 years ago and that was on a butane/propane gas mix) to replace the nylon gas pipe with a copper one, and to drill out the burner venturi.

With the loco partly disassembled I managed to push out the combustion chamber side walls a bit. Re-assembled the loco and off it went on my test track actually running reasonably slowly. When the standard Mamod safety valve went off it affected the burner pattern so the flames came out the chassis air slots, and whilst struggling to fit a 3 link chain to my multi-height coupling the burner started to pop-back to the jet as it was getting too hot.

However after coupling up some rolling stock off it went around my test loop with no more burner pop-backs and interestingly no more random speed bursts that it used to suffer from occasionally. The loco continued to happily run with slight adjustments to the gas & regulator until the water reached the minimum level (gas tank is too big on these locos).

So on the William II they put reheat tubes in the boiler, lowered the ceramic material in the burner and opened out the hot air/burnt gas slots on the top of the side tanks which would all improve steam production compared to the William. But adding an 'O' ring to the piston with the same small capacity lubricator seems to have added a stiffness to the William II which the steam production cannot keep up with.

Chris Cairns.

dougrail · Post by **dougrail** » Sat Mar 16, 2013 10:13 am

It would seem with the W2 the o-ring might have been the wrong type required for the job? It's interesting though just how these small-seeming modifications can greatly affect the burner and in turn the locomotives.

steamie1 · Post by **steamie1** » Sat Mar 16, 2013 10:28 am

If you modify the Mk2 and it works well let me know I'll do mine.cheers!

Chris Cairns · Post by **Chris Cairns** » Sat Mar 16, 2013 10:42 pm

It would seem with the William 2 the 'O' ring might have been the wrong type required for the job?

With all the other design problems (burner venturi, combustion chamber shape and mounting, etc.) I do wonder if this is the case as well.

On all other 'O' ring pistons I've seen (Mike Chaney, IP Eng, Dream Steam, PPS Steam, RWM Models & Roundhouse) they use a red or green coloured 'O' ring. With the William II & Brunel locos Mamod are using a black 'O' ring.

However once the piston gland housing has been pressed into the cylinder block it is not easy to remove again. I wonder if Mamod have any unassembled cylinders available so we could try using a different 'O' ring?

Chris Cairns.

dougrail · Post by **dougrail** » Sat Mar 16, 2013 11:19 pm

I can confirm that a set of supercylinders from Dream Steam manufactured July-Oct 2010 [rough guess on date = I'm dealing with Swordbreaker v1.0 here] [we're now on v2.1] had red o-rings. They were smooth rubber, easy to flex.

A second set of cylinders - a standard set, with upgrade kit pistons [suspect DS manufacture again; date unknown; source being...my spares] had the same type of o-ring, ie, red and smooth but different size.

What are new Mamod like? Easy to flex? Hard to flex? You say black, I'm getting a feeling [correct here with the facts] they're stiffer to say, squeeze or flex?

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Sun Mar 17, 2013 1:20 pm

Mamod O rings are made of nitrile which is ideal as it is resistant to petroleum substances as well as a high range of temperatures. Nitrile O rings are usually black although I have seen them in other colours so I don't think the colour is particularly significant.

On the other hand silicon O rings are usually red, but again can be other colours as well. Silicon wouldn't be as suitable for loco cylinders as it can be attacked by some petroleum substances.

Mike

dougrail · Post by **dougrail** » Sun Mar 17, 2013 1:46 pm

I'm using the colour only as a means to identify them. I'm just wondering whether the o-rings in the slide-valves are the right type/too stiff?

Chris Cairns · Post by **Chris Cairns** » Sun Mar 17, 2013 4:27 pm

Unfortunately most types of 'O' rings are available in most of the colours, so colour alone is no way of identifying the type of 'O' ring used.

It is not the Shore Hardness (Doug's flexing, but most are of a standard Hardness) but the type of material used that is important.

Silicone is not suitable for wet steam, all but one source I reviewed on-line say that Nitrile is also not suitable for wet steam, with Viton or EPDM being the choice for wet steam. So if Mamod are indeed using Nitrile then that might be causing the stiffness problem which is being hidden by the 'lack of steam' theory.

Over on Hornby OO Live Steam we are experiencing a similar stiff running locomotive problem (but it does not affect every locomotive, as they are all very individual in their performance), and the Supporters Club are doing a trial with red Viton 'O' rings. Unfortunately I've still not fashioned the oddly sized spanner to remove the piston gland housing so have not joined in on that trial yet.

Chris Cairns.

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Sun Mar 17, 2013 4:41 pm

A good few weeks back, when Mamod first said they were having problems sourcing O rings of exactly 11mm OD (apparently the only ones they could get measured 11.2mm OD) I had a dig through my spares box and came across an unopened packet of rings which measured exactly 11.0mm OD. I offered them to David Terry to try and he said they would be fine so long as they were made of Nitrile, which they were.

From that conversation I presume Mamod O rings are made of Nitrile.

(It turned out that the O rings I sent had an internal diameter of 7mm while Mamod needed 7.5mm, so I don't believe they were ever used).

Mike

spooner · Post by **spooner** » Sun Mar 17, 2013 5:53 pm

One thing with O rings that they have to have another room to roll in thee slot.

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