Bubble oil stove air inlet flap valve

[Bro]

On my smallish NB (40 ft) I've always had problem getting the Bubble oil stove (corner type) to run at low enough temperature with a blue flame. Boat can get too hot!

 

Possibly it's too big a contraption for the cabin volume but nonetheless ........................... I've been experimenting and found that if I part block (cover) the air inlet I can then reduce the fuel flow setting on the Toby valve, still get a blue flame and Bingo, lower temperature. Sorted!

 

Now, the air inlet takes the form of a flap valve which is gravity biased on my stove to wide open when stove is cold or at low temperature. This seems counter intuitive as I would expect it to be nearly closed so that when the temp setting is raised, more fuel flows, temperature rises, more draft is created and flap valve is drawn progressively more open.

 

If I turn the flap valve assembly t'other way up it then does becomes biased closed and should progressively open as temp rises (shouldn't it?). So, is my flap valve assembly fitted incorrectly to the stove?

 

When next on the boat I'll turn the valve other way up and see what happens but meanwhile I'd be interested to know how other Bubbles are set-up. If turning it does the job it will save me the hassle of making up a proper adjustable air blanking plate rather than continue with the current experimental lash-up.

 

If anyone out there has an oil Bubble I be grateful if they would look at their flap valve and let me know if it's biased open or closed.

 

 

[koukouvagia]

My Refleks doesn't have one of these dampers, but looking up the Bubble Stove installation instructions I read the following:

 

Any slight reduction in the flue gas temperature will reduce the chimney vacuum or pull, hence when the stove is slowed down for all night burning, as the flue gas cools down the chimney vacuum reduces and as the chimney vacuum drops, the stove may well start to burn sooty. This problem is highlighted even more during very cold weather when the chimney can cool down even faster. To help control conditions of excessive vacuum the appliance has a built in swinging barometric damper designed to swing open and spill air into the chimney should the vacuum suddenly increase. The swinging damper is located at the rear of the appliance.

 

I'm not sure whether this helps or not, but it does explain how the damper is supposed to work.

 

eta: I've just found a bit more information.

 

Note Barometric dampers attempt to control excess flue vacuum by spilling air into the flue thus reducing the vacuum applied to the burner. Every Year Applies to BB1 – BB2 and Belfort 1. The barometric damper must be cleaned to remove any build up of dust and checked to make sure that it swings freely and is correctly adjusted. 2. The damper will only swing open under conditions where the maximum chimney vacuum is exceeded, normally this will be anything over .05”-.06” W.G. 3. At any vacuum below this figure the damper should be in a closed position. Apply WD40 to the spindle tips.

Edited November 18, 2015 by koukouvagia

[rjasmith]

No one with a Bubble has answered you yet but I have a Kabola E5 vaporising burner boiler which is identical in principle to the Bubble.

 

I think you are absolutely right in your description of how the draught compensating damper should work. On the Kabola the damper has a small adjustable counterbalance weight which needs to be set so that the damper is just biased SHUT under normal conditions (definitely not biased OPEN).

 

If there is a sudden increase in draught, eg because of a wind gust outside, the damper will briefly swing open to stop it affecting the flame. When the wind gust has died down the damper should swing shut again. A boat flue is very unlikely to create a standing flue draught strong enough to hold the damper open because the flue is too short

 

I assume you don't have a manual for your Bubble? They are all available to download on Harworth Heating's website (an absolutely fabulous place for all manner of stove manuals). Look here and choose the right manual from the menus. I've just had a look at one of the Bubble stove manuals and the way yours is working is definitely NOT how they describe it!

 

Richard

 

Damn KK always types faster than me!!

Edited November 19, 2015 by rjasmith

[Bro]

My Refleks doesn't have one of these dampers, but looking up the Bubble Stove installation instructions I read the following:

 

Any slight reduction in the flue gas temperature will reduce the chimney vacuum or pull, hence when the stove is slowed down for all night burning, as the flue gas cools down the chimney vacuum reduces and as the chimney vacuum drops, the stove may well start to burn sooty. This problem is highlighted even more during very cold weather when the chimney can cool down even faster. To help control conditions of excessive vacuum the appliance has a built in swinging barometric damper designed to swing open and spill air into the chimney should the vacuum suddenly increase. The swinging damper is located at the rear of the appliance.

 

I'm not sure whether this helps or not, but it does explain how the damper is supposed to work.

 

eta: I've just found a bit more information.

 

Note Barometric dampers attempt to control excess flue vacuum by spilling air into the flue thus reducing the vacuum applied to the burner. Every Year Applies to BB1 – BB2 and Belfort 1. The barometric damper must be cleaned to remove any build up of dust and checked to make sure that it swings freely and is correctly adjusted. 2. The damper will only swing open under conditions where the maximum chimney vacuum is exceeded, normally this will be anything over .05”-.06” W.G. 3. At any vacuum below this figure the damper should be in a closed position. Apply WD40 to the spindle tips.

 

The flap valve I'm talking of is positioned at the front of the stove definitely not "rear of the appliance". Also, the text refers to stove types "BB1 - BB2 and Belfort 1" not my Corner Stove which is a different animal. Many thanks KK but I think we are barking up the wrong tree here.

[Bro]

No one with a Bubble has answered you yet but I have a Kabola E5 vaporising burner boiler which is identical in principle to the Bubble.

 

I think you are absolutely right in your description of how the draught compensating damper should work. On the Kabola the damper has a small adjustable counterbalance weight which needs to be set so that the damper is just biased SHUT under normal conditions (definitely not biased OPEN). If there is a sudden increase in draught because of a wind gust outside (a boat flue is very unlikely to create a standing flue draught strong enough to hold the damper open because the flue is too short.

 

I assume you don't have a manual for your Bubble? They are all available to download on Harworth Heating's website (an absolutely fabulous place for all manner of stove manuals). Look here and choose the right manual from the menus. I've just had a look at one of the Bubble stove manuals and the way yours is working is definitely NOT how they describe it!

 

Richard

 

Damn KK always types faster than me!!

 

Thanks RJ for the link to Harworth Heating website.

 

In the text for Corner Stove we find it says:- "The amount of oil that can be successfully burned is directly proportional to the amount of air that the chimney can draw into the pot and so to achieve adequate combustion a balanced and appropriate flow of both oil and air is required."

 

This seems to be saying that to maintain a proper fuel air balance ratio more air must progressively be drawn into the pot as fuel flow is increased (for higher temp settings). This makes sense and in which case the air inlet (flap valve) must surely be biased closed to then progressively open as more fuel is fed in to increase the temperature.

 

Methinks that in the past some Charlie has fitted the flap valve upside down on my stove and consequently the stove has not been able to achieve proper low temperature settings, hence I'm always too hot.

 

Shan't be back to the boat for week or so but first job will be to turn the flap valve t'other way up and see how it works. Watch this space!

 

Would still like to hear from Corner Bubble owners about their flap valve positions (if you'll forgive the expression).

Edited November 18, 2015 by Bro

[peterboat]

just lit my bubble to see what happens it is closed and set on a low blue flame hope this helps

[Ex Brummie]

The standard bubble has no control to air intake as the bottom is totally open and draws as much air as the flue pull demands. This is the principle that all vaporising burners work on. The main problem with vaporising burners on boats is that the flue is never long enough to produce the optimum draught, and the length of flue outside the boat rarely maintains the same 4" diameter of the inner flue, and also is often only single skinned so cools down too quickly. My Bubble has a draught stabiliser in the rear of the burner chamber, and if the flue draught become too great, it opens to stop too much air being pulled through the burner perforations.

I also have a length of 4" pipe fixed into the outlet of the collar, and a conventional chimney around this too help it retain heat. This is topped off with a Swedish cowl to eliminate downdraught and reduce external wind pull.

The evidence of blue flame at low settings can be almost non existent, and as long as the catalysers are red, then that should be low enough. Too low a fuel supply cannot sustain a flue temperature sufficient to maintain flue draught, thus reducing combustion air. This makes yellow flame and soot. In a small cabin, the minimum output of a bubble, over a few hours, will prove too much heat.

[Bro]

The standard bubble has no control to air intake as the bottom is totally open and draws as much air as the flue pull demands. This is the principle that all vaporising burners work on. The main problem with vaporising burners on boats is that the flue is never long enough to produce the optimum draught, and the length of flue outside the boat rarely maintains the same 4" diameter of the inner flue, and also is often only single skinned so cools down too quickly. My Bubble has a draught stabiliser in the rear of the burner chamber, and if the flue draught become too great, it opens to stop too much air being pulled through the burner perforations.

I also have a length of 4" pipe fixed into the outlet of the collar, and a conventional chimney around this too help it retain heat. This is topped off with a Swedish cowl to eliminate downdraught and reduce external wind pull.

The evidence of blue flame at low settings can be almost non existent, and as long as the catalysers are red, then that should be low enough. Too low a fuel supply cannot sustain a flue temperature sufficient to maintain flue draught, thus reducing combustion air. This makes yellow flame and soot. In a small cabin, the minimum output of a bubble, over a few hours, will prove too much heat.

 

Mine is not a "Standard" Bubble but a "Corner" Bubble. It has no draft stabiliser in the rear, it has an air inlet contraption (I call a flap valve) at the front of the stove and near the floor. It's possible the two types operate on different principles. Where do we go from here?

[Bro]

just lit my bubble to see what happens it is closed and set on a low blue flame hope this helps

 

Hope you don't mind, I sent you a PM.

[Ex Brummie]

The amount of heat that is produced is entirely dependent on the quantity of fuel consumed. This is an undeniable fact no matter what the fuel is. All bubble stoves incorporate vapourising burners which are designed to draw as much air as is needed for efficient combustion. The more fuel fed into the burner, the more heat is generated in the flue and it draws faster increasing combustion air supply through the holes in the combustion pot. To reduce the heat, reduce the fuel flow, but if you go too low, then insufficient heat is produced to sustain combustion.

The combustion air restrictor on your corner bubble will be wide open normally, and will counteract gravity when an external influence (excess chimney draught from wind) cause a greater airflow through the burner which can lift the flame and extinguish it.

There is a minimum level at which the stove will operate, and at 4cc/min fuel flow this will be around 2 -2.5 Kw. As this is heating up a mass of metal, over a moderate period of time, if the area is well insulated and draughtproofed, in a small boat, this can become oppressive. The answer is to let in more ventilation to dissipate heat, or turn the fire off.

If you want to confirm the position of the combustion air restrictor, then the manufacturer is the best source of information, but as a professional technician with this type of equipment, trust me.

[Bro]

The amount of heat that is produced is entirely dependent on the quantity of fuel consumed. This is an undeniable fact no matter what the fuel is. All bubble stoves incorporate vapourising burners which are designed to draw as much air as is needed for efficient combustion. The more fuel fed into the burner, the more heat is generated in the flue and it draws faster increasing combustion air supply through the holes in the combustion pot. To reduce the heat, reduce the fuel flow, but if you go too low, then insufficient heat is produced to sustain combustion.

The combustion air restrictor on your corner bubble will be wide open normally, and will counteract gravity when an external influence (excess chimney draught from wind) cause a greater airflow through the burner which can lift the flame and extinguish it.

There is a minimum level at which the stove will operate, and at 4cc/min fuel flow this will be around 2 -2.5 Kw. As this is heating up a mass of metal, over a moderate period of time, if the area is well insulated and draughtproofed, in a small boat, this can become oppressive. The answer is to let in more ventilation to dissipate heat, or turn the fire off.

If you want to confirm the position of the combustion air restrictor, then the manufacturer is the best source of information, but as a professional technician with this type of equipment, trust me.

 

 

Thanks Brummie.

What I've been calling a flap valve is in fact properly called an Air Restictor and this is the device fitted to Bubble "Corner"Stoves (but not to Standard Bubble, BB1, BB2 nor Belford which have Barametric Dampers it seems). Anyway, I find that by blanking off a good deal of the airway to the Air Restrictor I can turn down the fuel flow and significantly reduce the stove temperature whilst still maintaining complete combustion (blue flame). What more can I say!

 

As you point out fuel flow rate for the Corner Bubble is stated 4-10cc/min. Interestingly though I discover a Harmony oil stove rated at 1.5 - 5kW and which uses similar Toby valve has a minimum flow rate of 3cc/min:-

 

Harmony 11 Oil Stove

The Harmony 11 is identical to the Harmony 5 oil.

Maximum heat output: 5kW

Minimum heat output: 1.5kW

Flue outlet: 101mm internal diameter

Burner size: 6 inches

Oil type: C2 kerosene, heating oil

Oil valve: Toby

Flow rate: 0.18L/hr Min, 0.72L/hr Max

Oil Valve Toby 4-12cc, Part No: 32807:-

Toby oil control valve 4cc to 12cc fitted to the Harmony 5,,Harmony 11, Harmony 21, Stanford 50 and Toledo oil stoves. This valve may need to have the flow rate reduced as the original one, no longer available, was only 3cc.

So, by reducing the air flow through the Air Restrictor possibly the Bubble Corner stove can be made to run at 3cc/min (same as Harmony 11) and if so what do you think the heat output then might be? 75% of your 2-2.5kW? Say 1.7kW (Harmony claims min of 1.5kW).

 

Great Forum this! Lots of helpful people who know what they're talking about.

Edited November 22, 2015 by Bro

[peterboat]

sorry it has taken so long to get back to you i now have a bb1, my old boat had the corner stove which had the same workings as yours i remember having problems with it in the early days with the flap assy being seized open i have had the same issue with the bb1 s flap being seized as well. i was lucky in that terry from bubble is very close so he sorted my stove as a favor and once set no more problems were had

[Ex Brummie]

With regard to reducing the oil flow, trial and error may achieve the objective. What you need to bear in mind is that the pot and catalysers need to be kept at a temperature that vapourises the fuel. If you do turn it down, make sure you check it after an hour or so as it will take that long for the full effect to be assessed. Also bear in mind that as the outside temp gets cooler, it will also cool down the flue and reduce the combustion air pulled through the pot, thus making soot. For this reason, they are best run a little hotter to maintain the flame. I often find that during the evening on a cold day, I have to lose a little cabin heat, but with the control set to minimum, as the outside temperature drops, so does the flame and stove heat.

[Bro]

With regard to reducing the oil flow, trial and error may achieve the objective. What you need to bear in mind is that the pot and catalysers need to be kept at a temperature that vapourises the fuel. If you do turn it down, make sure you check it after an hour or so as it will take that long for the full effect to be assessed. Also bear in mind that as the outside temp gets cooler, it will also cool down the flue and reduce the combustion air pulled through the pot, thus making soot. For this reason, they are best run a little hotter to maintain the flame. I often find that during the evening on a cold day, I have to lose a little cabin heat, but with the control set to minimum, as the outside temperature drops, so does the flame and stove heat.

 

Good advice much of which was not obvious at first sight to me. Waiting for pot and catalyser to stabilise before settling on fuel flow, and certainly you make a good case for well insulated chimney. Insulating the chimney I can do as I have 90mm dia. flue which extends to run through a standard double walled 6" chimney (so can seal gap between the two at top of chimney).

 

Thanks.

Edited November 23, 2015 by Bro

[Ex Brummie]

No fires are perfect, but after 7 years with a squirrel, the 17 years of Bubble have been Nirvana. It still takes maintenance, and as I don't live aboard, all I do each time I light the fire is spend 2-3 mins scraping the bottom of the pot and turning the de coke lever on the inlet. Having a constant heat is so comfortable. My Bubble is probably the best thing I have put on the boat. Mine has a backboiler and is fitted at the rear of the cabin, the saloon, with a gravity fed radiator to the front bedroom. The gravity circuit is on 15 mm (it will never work) but with the flow insulated with pipe insulation, it does and there is not a lot of water to heat up.