More on those Mamod speed bursts

[Chris Cairns]

A phenomenon which seems to have affected most Mamod locomotives made since 2003 is seemingly random speed bursts for a set regulator position. To different levels it has affected my William, William II, Mark I (one of the original Mamod Train's), Mark II & Diamond Jubilee locomotives.

The commonalities -

1. A horizontal externally fired pot boiler, with the steam pipe routing through the burner output. No functional steam dome like previous Mamod SL/MSS's.

2. Gas fired.

3. Steam take-off on top of boiler at the rear.

4. All lubricated using Mamod 460 steam oil (Mamod Train/Mark 1 not fitted with a lubricator, I have retro-fitted a Dream Steam dead leg lubricator).

The differences -

1. Not all fitted with 'O' ring pistons.

2, Different design and position of lubricators (Mark II & Saddle Tank total displacement lubricator in cab, dead leg type lubricator fitted at front of William & William II).

3. Not all fitted with boiler reheat tubes (none on William).

Results from Lloyd (steamie1) on his Mark II 'Charles' -

I found out that the Roundhouse ISO 220 seems to give less fast spurts.

Results from Mike Wakefield's Mark II -

On both occasions, using the ISO 220 I didn't observe any speed bursts, using ISO 460 I experienced 2 - 3 speed bursts, and using ISO 680 there was one slight speed burst on the first run and none on the second.

My results -

William - Since drilling out the burner venturi it no longer suffers from speed bursts.

William II - Again no speed bursts since drilling out the burner venturi.

Mark I - Burner venturi drilled out but still suffers from speed bursts. Using Roundhouse ISO 220 steam oil it suffers from less speed bursts and runs freer - just waiting for the dead leg lubricator to cool down to check the level of oil used.

So using Roundhouse ISO 220 steam oil seems to give the best results.

One theory posted on these Forums is the speed bursts are being caused by water 'flash boiling' in the 'superheater'. So why are the Mamod SL/MSS/IP Jane's not affected by these speed bursts?

Another advantage of the Roundhouse steam oil is being thinner it makes less of a sticky mess on the bottom of the chassis of my Mark I below the cylinders and reverser valve making it easier to clean up after running. Be interesting to compare how it will work in my Mark II & Saddle Tank locos which have a shorter exhaust pipe and displace all of the oil out of the lubricator (Mike reported it affected his burner more than using ISO 460 steam oil).

Chris Cairns.

[Chris Cairns]

Mark I - So it uses more of the oil in the dead leg lubricator when using the Roundhouse 220 steam oil, compared to 460 steam oil.

William - 1st run was not conclusive as I had not oiled the ends of the piston valve rod and the piston rod (trying to keep the 2 oils separated but ran out of pipets/syringe needles). 2nd run confirmed that 220 steam oil works OK.

Next to try are my William II (which has only 3 wheels at present and needs a new copper gas pipe trimmed) and my Mark II & Saddle Tank locos.

Chris Cairns.

[mikewakefielduk@btinterne]

If your Mk1 more 220 oil in the dead leg lubricator then it surely must empty a Mk11's lubricator at a rate of knots, which probably explains why I was having issues with oil getting onto the ceramic burner.

Anybody got any ideas how you could fit an adjustable needle valve into a Mk11 lubricator to regulate the oil flow? Anybody got an old Regner lubricator spare?

Mike

[Chris Cairns]

Took me some time to find it but we discussed the Mamod lubricator in the New Mark II Topic.

Did you not manage to fit a continuous steam pipe to the Mamod lubricator you obtained?

The problem with the Mark II & Saddle Tank locos is Mamod do not fit a decent size exhaust pipe, and the chimney is just an open piece of pipe, so even if you extend the exhaust pipe the condensate will fall back onto the front footplate and be sucked into the burner. I've fitted a strip of brass to try and protect the burner but I need to get a wider piece of brass sheet to make a proper deflector plate.

And how do you refill the lubricator? I think refilling the lubricator with the locomotive on it's side means that some of the oil has already managed to get into the steam exit pipe before the run starts. I've started refilling the locomotives with them remaining vertical to try and delay the displacement of the steam oil.

Chris Cairns.

[mikewakefielduk@btinterne]

No, I never got around to altering the spare lubricator. I got distracted thinking about using it instead for a oil trap for the exhaust of the Brunel, but in the end its still sitting on the desk in front of me, part of the To-Do list of things that keep getting put off until I have more time. Unfortunately life at the moment seems to be getting busier not the other way round.

I've made the roof of my Mk11 detachable so I can get at the R/C servo a bit more easily, so refilling wouldn't be to much of a problem. Emptying would have to be done using a syringe I guess. I need to think about it some more though.

Mike

[Chris Cairns]

William II - Works well on Roundhouse 220 steam oil with no speed bursts.

Mark II next.

Chris Cairns.

[mikewakefielduk@btinterne]

It would be somewhat ironic if all Mamod needed to do to fix the Thomas Telford was to use a thinner steam oil.

Mike

[Chris Cairns]

Mark II - No speed bursts on 220 steam oil. However as Mike has already posted you do get a fair amount of the oil displaced out of the exhaust at the beginning of the run, due to the total displacement design that Mamod have used. I do get about the same amount of oily condensate displaced when I use 460 steam oil.

My Mark II is one of the original batch, and unlike later batches it has a short piece of copper tubing (just under an inch long) pressed onto the exhaust pipe so that this extension takes it into the chimney. I tried fitting a piece of silicon tubing over the exhaust pipe to bring the exhaust further up the chimney, but that caused the exhaust to condense more causing a slight increase in back pressure and reduction in running performance. So I refitted the short piece of copper tubing and the loco ran better. Should really try it with my Summerlands Chuffer to see what difference that makes (it worked well in my Diamond Jubilee Saddle Tank).

One downside of using 220 steam oil is it makes the track slicker so I'll need to include using a degreaser in my running regime - having ran several locos over my test loop recently the Mark II was occasionally wheel slipping with a heavy load.

Next to try with the 220 steam oil is my Brunel which, although it does not suffer from these speed bursts (different boiler & burner design), it does suffer from stiffness during running which I suspect is to do with the 'O' ring piston.

Chris Cairns.