More on those Mamod speed bursts
Posted: Wed May 01, 2013 11:07 pm
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.
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.