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Dirty Gas ?


thebishbus

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Hi all you gas experts. I see mentioned that a possilbe cause of a gas appliance sooting up, is dirty gas. I have some questions about this dirty gas.

 

1. - - - - If dirty gas is the problem, would this not show up on the all gas appliances being used , ie, the fridge, water heater and hob unit.?

 

2. - - - - If there is contamination in the gas,will some remain in the cylinders, and contaminate the new clean gas when refilled. ?

 

3. - - - - If this contamination remains in our refillable cylinders when empty ,should we attempt to remove it ? ie , remove the cylinders, turn upside-down, leave with valves open to drain out.

 

Brian B.

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Not a gas "expert", but - if the fridge is sooting its exhaust, it indicates that correct combustion is not taking place, most probably because the gas/air ratio is incorrect. This may be because of an obstruction within the very tiny jet, reducing gas flow, or because of some obstruction to the air supply, such as a cobweb, or because of obstructions to the flue. If not already done, therefore, I would suggest first getting the fridge gas side serviced by a competent person.

 

If that doesn't clear the problem, it may be due to a problem with the gas. Other appliances may well operate normally because, compared to the fridge, they are gross consumers so, although the balance between gas and air is equally critical, it is much easier to maintain within reasonable limits.

 

So far as I am aware, all LPG is to some extent contaminated. That is to say there are traces of oil present, and there is also a powerful scent added to make leaks readily apparent, whether the cylinders are exchange or re-fillable. In theory, these additives burn off with the gas, but Autogas is supplied from filling station bulk tanks which, due to low turnover, may accumulate some "sludge", and is designated for LPG powered vehicles, where it remains in liquid form right up to the engine, and is in any case only consumed while the vehicle is in motion, so ensuring a certain amount of agitation of the liquid reserve.

 

On the other hand, when Autogas is used in motorhomes, it evaporates from the surface of the liquid reservoir, and only enters the motorhome system in gaseous form. Since most motorhome installations are in use only when the vehicle is stationary, there is greater possibility that the contents will settle out and stratify within the cylinders, leading to the heavier additives accumulating somewhere in the resulting "stack". The longer the vehicle remains static, the greater this possibility. The lower the liquid level, the greater the possibility that relatively high concentrations of these contaminants/additives may begin to evaporate into the stream, possibly causing the sooting you can see.

 

I believe I am right in saying there is a general recommendation for re-fillable cylinders to be periodically purged and cleaned to rid them of accumulating oil and scent additives. Maybe your cylinders are due a flush out. Their manufacturer/supplier should have recommendations for the frequency of this procedure. However, if the fridge is serviced, the sooting continues, and all other appliances continue to operate normally, it may be that, irrespective of the time you have had the cylinders, they should be evacuated and cleaned out to remove any accumulation of sludge.

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Never heard of "dirty gas"

Brian is absolutely correct with his reply. Any signs of soot anywere on any gas appliance is a serious problem and must be sorted asap. As a gas safe reg business / chap I can only reccomend that you get it checked by a competent engineer (good luck finding one with the relevent ticket cos there like rocking horse stuff)

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Thank you for the answers. The reason for my query re " dirty gas" was due to our experience this year.

We have two 11kg Gaslow cylinders, with auto change-over valve, one was full, and one nearly empty, I refilled this cylinder before our months holiday in France. For the first two weeks we did not have hook ups so used gas all the time, the auto change-over valve was still set for the now refilled cylinder. Straight away there were sooty deposits above the fridge vent, no problem with the water heater flue outlet or hob flame, the fridge worked normally. By the end of that holiday we had just emptied that cylinder.

When we got home, I removed the fridge burner covers, and the flue pipe. I found that black paint was flaking off the flue pipe and had dropped around the burner assemby. I cleaned all the soot and paint bits away, repainted the flue pipe with high temperature exhaust paint, reasembled, tested, OK no soot. But now of course it was running on the other cylinder.

My concern is, was the flaking paint causing the sooting, or "dirty gas " in the other cylinder,? and do I need to clean the cylinder before refilling it .?

Brian B.

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There is a tendency for LPG to be classed as a dirty gas compared to natural gas. Occasionaly solid particulates get carried over but it gets noticed more in LPG due to the smaller holes in the injectors which get blocked easier. I get called to more pilot light problems with LPG than natural gas.

Any dirt on your burner will cause a problem with the combustion, that is why your service engineer should always strip your appliance down and clean the burner.

The reason there are not many engineers who service caravans/camper vans is because it costs money to get a ticket to touch caravan/camper vans which has to be renewed every five years. Some of the gas appliances on caravans are awkward and take time to strip down. This stacks the bill up and some people just dont want to pay . In the end, having a ticket can be more trouble than its worth.

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That is interesting Dave, what you say about sooting showing up on cooking pans, we had none that, nor sooting from the water heater flue outlet. I think therefore our problem was due to the build-up of flaking paint around the burner assembly.

Thinking about it, although we had been away for several short breaks early in the year we only used the fridge on 12 volt and mains. The first time we used the fridge on gas, after laying the van up over winter, was in France in July, the sooting was noticeable after a short tme. Since removing all the paint debris it seems fine and had a good four day test at Lincoln.

It may be worth other people with older vans checking their fridge flue pipes for paint peeling and rusting, not just their burner units, before other problems arise.

Brian B.

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