Posted by: Mark Drake
Date: August 28, 2007 07:55AM
As I feel that it’s very important that we should all share as much information as possible, good or bad, I’ve had a recent experience that we may all benefit from…
I drive my 735 regularly, mostly to work and back – a round trip of just less that 40 miles – it turns a chore into a delight! So far I haven’t had any problems that I can’t deal with on the roadside – until last Friday that is…
On my return home in the evening, I noticed the burner note changing more and more. Thinking that the fuel jets may need a clean, I pulled into a convenient layby and set about the job. On opening the side flap to access the burners I was horrified to see a small dribble of water from one of the venturis and the pilot extinguished. Clearly some leaking tubes in the boiler. I have to admit that I was a little surprised as I have never scorched the boiler and treat it with great respect; always blowing down, regular washouts, that kind of thing.
I judged that although I could probably press on with the journey, I was losing water from the boiler and any hold up would probably force me to stop. I was also concerned that further leakage may crack the burner plate etc, etc, so I admitted defeat and got home courtesy of the RAC.
On dropping the burner the next day, I noticed a surprising amount of debris, mostly oxide flakes sitting in a heap on top of the burner plate. I have to admit that earlier in the season on inspecting the fire tubes, I noticed that the tubes around the pilot to be slightly sooty so gave the offending tubes a jolly good sweep out; about 200 tubes in the affected zone. I hadn’t considered the volume of material to be a problem – but maybe it was. To make matters worse, I hadn’t thoroughly cleaned the burner for over a year.
The debris had accumulated on the burner plate in an area about 5” or 6” diameter, effectively blanking this area. I suspect that there was then a ‘cold spot’ in the fire which may have lead to sufficient thermal differential in the lower tubeplate to cause leakage.
It’s possible that the debris stayed in the same area on the burner plate as a consequence of ‘Chladni patterns’. These are the patterns that sand, etc. will form on a flat plate if the plate is vibrated. My burner howls (a lot less than it did, thank goodness) at a fairly stable frequency, which may have caused the debris to build up the way it did.
Anyway, I’ve expanded the tubes that still ‘beaded’ under hydraulic test and it will hold 500 lbs on hydraulic OK now. Ran out of time to do a steam test though.
When I ran the burner off the car it howled really loudly, and by putting a steel rod on the burner plate when howling the vibrations I felt were most intense. The burner burns very unevenly, so I’m going to investigate in detail over the next few weeks.
Moral of the story – keep all parts of the burner scrupulously clean, if you sweep the tubes remove the burner first. Check that the burner is burning evenly and if you notice any change in tone, investigate it. A change in tone means that something has definitely changed.
I will keep you posted on my progress, I get married in 6 weeks time so steam car stuff may have to wait a while…
I hope that someone finds this useful!