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[kiwimodeller]

Hi, I wondered if anybody has done any experimenting in to the causes and cures for whistling noises from the boiler? I have a Cheddar Puffin horizontal Version 2. It has always struggled to keep up sufficient pressure to run the little Saito V4 that it is connected to. I have tried various ways to increase the operating pressure and to reduce the demand for steam with some success but this engine is smaller than the Cheddar Puffin so I was disapointed with the boiler performance. After asking previus questions I was directed to Jerry at Clevedon Steam (who incidentally has a new website http://www.clevedonsteam.co.uk/ as well as the Ebay shop) and purchased one of his metal gauze burners to replace the Cheddar ceramic one. After various tuning experiments and after changing from a number 5 jet to a number 8 I am now getting a better steam supply, still not as much as I would like but better than before. Along the way I learned some interesting stuff including that a good boiler/burner setup should maintain operating pressure with the valve fully open even if the steam pipe is disconnected from the engine. My problem now is that when operating at its best settings the boiler makes a loud whistling noise constantly. The higher the gas setting, the louder the whistling noise. I understood that this was a symptom of lean burning mixture but with the number 8 jet the flame should be rich compared to the 5. I was going to drill some extra secondary air holes in the burner casing to allow more air in to mix with the extra gas but want to sort the noise out first. Jerry's suggestion, based on research done at Cheddar, is to drill a small hole in the endcap of the flue at the opposite end of the boiler to the burner. This is supposed to breakdown harmonics caused by the gases swirling around the cross tubes. Before drilling a hole in my boiler I thought I would see if anybody had found another way to stop the noise. Thanks, Ian.

[south steyne]

Hi Ian I have the same burner in my boiler which works very well with the same whistling noise ,fitting a chimney 1" diameter and 4" high cancelled out the noise hope it works for you with a little bit of experimenting
John

[kiwimodeller]

Thanks, willing to try any reasonable suggestions and it would not be hard to make another funnel so I will give that a go and post the result. Cheers, Ian.

[kno3]

Altering the length of the chimney should change the pitch of the "pipe". Try experimenting with a piece of aluminium pipe before cutting up the original chimney.

[kiwimodeller]

Had a measure up today and the original Cheddar funnel is 1" I D and 4" high. I have a selection of copper pipe so I made up another 5" high and will try that at the lake tomorrow, weather permitting, and post the result tomorrow night. Thanks for the input.

[tobyker]

This has great potentail. Build, at once, a variable length sliding section funnel and you will be able to play tunes all round the lake, a la swanee whistle.

[kiwimodeller]

Tried a longer funnel of the same diameter as the original (1" I D ) today. Although the whistle was not as loud and perhaps a little lower tone but certainly did not fix the problem. Rain came and I went home but on the bench I also tried a slightly larger diameter funnel which made a louder noise if anything, certainly no quieter. Gas pressure and jet position/mixture strength do make some difference but I certainly have not found a cure yet. Looks like I might have to try the hole in the end of the boiler as Jerry suggests.

[derekwarner]

Ian....just thinking about this...  it is a little different than attaching an alternate muffler to an automobile engine 

The inherent boiler sound/whistle/noise is a function of the air draw & combustion characteristics of the boiler @ the other or front end of the boiler  .......& not of the exhaust pipe....  Derek

[kiwimodeller]

Understand the analogy Derek but muffling the noise a bit more would be enough to make me happy. I believe my initial problem was that the combustion was not good enough to make sufficient steam. I seem to have almost solved that but at the same time have introduced the whistling problem. I am reluctant to go backwards but as yet have not had the courage to drill a hole in the end of the boiler to see if that will cure it. If no other ideas are forthcoming then I guess I will just have to give it a go. Thanks for the contribution. Cheers, Ian

[south steyne]

 )Hi Ian have you tried to adjust the air flow at the collar of the burner there are about 4 or 5 holes there perhaps a collar around it and adjust the flow may stop the whistle .
John

[MichaelK]

Hi Kiwi,
I've got  a Minature Steam 3 1/2" boiler which "SOMETIMES" makes a whistling noise.
I put my hand over the top of the funnel, not for long, (don't extinguish the flame, or burn your hand,) and the noise normally goes.
Mick
 

[kiwimodeller]

Thanks for the suggestions Mick and John. I have tried holding cloth etc over the funnel which alters the tone but does not make the noise go away. Blocking off one of the four secondary air holes with a finger wrrapped in wet cloth does stop the noise but it also cuts down the flame and once again I do not get enough steam. I was thinking of drilling one or two more holes so the air does not have to rush through the holes so much but the manufacturer of the burner did not reccomend this in case it messed up the mixture. He is convinced the problem is resonance on the cross tubes and that a hole in the other end of the boiler will fix it, I guess I will just have to bite the bullet and give it a go. Cheers, Ian.

[ooyah/2]

Hi Ian,
What do you mean by drilling a hole in the Boiler?
Where in the boiler do you propose to drill a hole ?
 George

[kno3]

Before drilling the boiler, try inserting a wavy strip of metal down the funnel into the flue, it might change the resonance mode.

[kiwimodeller]

Kno, I have tried various bits of rolled up wire mesh in the funnel and/or in the flue. These seem to help the heat transfer to the boiler but do not have much effect on the whistling. I have not tried wavy strips but am guessing you are meaning thin strips of  corrogated metal. I will look at that if you think it will help. George, the idea to drill a hole comes from Jerry at Clevedon Steam who used to work at Cheddar Steam. The Cheddar boilers have a flue that goes right to the far end of the boiler and is then blanked by what looks a bit like a domed frost plug. The funnel goes off the top of the flue internally. While working at Cheddar Jerry recalls experiments with a hole in the blanked end to stop the resonance. He suggests a 5mm hole to begin with and thinks that there will be very little heat loss out the hole, it being more likely that air will be drawn in and up the funnel. I can see the possible benefit but just dread drilling a hole in a perfectly good boiler! Cheers, Ian.

[ooyah/2]

Hi Ian,
What do you mean by drilling a hole in the Boiler?
Where in the boiler do you propose to drill a hole ?
 George

Hi Ian,
Not being familiar with your boiler I had visions of you drilling a hole in the boiler ( a pressure vessel ) and the ensuing stream of water and steam coming out of the boiler.
However it's drilling a hole in the back end of the firing tube which isn't such a big deal in as much if it doesn't work you can plug the hole.
George.

[GG]

This "noisy" boiler sounds awfully like my experiences with a steam plant, reported in the Oct 2010 issue of Model Boats.  The gas burner had its own characteristic but acceptable "roar" when fired out of the boiler.   When placed in the boiler, a horizontal centre flue type, a horrible loud sound was produced, a sort of rasping horn effect and not something to be welcomed at the pond side.
Adjusting the ceramic burners position could reduce the noise a little but removing the brass funnel which was plugged into the flue outlet on top of the boiler eliminated this sound effect totally.  This lead me to the conclusion that I was dealing with a Resonance Tube problem.  The modest sound made by the burner was setting up a standing wave inside the flue and funnel.
Luckily the nice shinny brass funnel would have affected the stability of my planned model, a slim early TBD, and had to be removed.  The replacement funnel section was made from thin aluminium sheet, same diameter but a different length.  This was sufficient to stop the resonance and the horrid noise.
Had I still access to suitable measuring equipment then the frequency of the offending noise could have been measured.  From the speed of sound, remembering that the resonance is occurring in the hot flue gas not cold air, the wave length could be determined.  By changing the funnel length by around 1/4 wave length it should have moved the resonance effect from a maximum to a minimum.  But, it was a lot easier with the aluminium funnel, to use the good old "cut and try" method!
Looking up "combustion driven oscillations" on the Internet can give you more information, For those with a musical bent, try "Pyrophone".
Glynn Guest