'spascher's exhausts.

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Graham_Wright

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Fitting my heater in a dark corner, I have noticed that, on full blast, the flexible stainless exhaust hose can actually glow red hot. There is a "rubber" gasket fitted between the heater and the surface it is attached to.
If that gasket can withstand "red hot" temperatures, what can it be made of? Further, can that material be used as an exhaust hose?
Silicone rubber is specced at 200°C continuous but red heat is over 500°C.
 
Their is an annular space around the exhaust outlet and rubberised gasket. Better get some form of heat resistant insulation on the exhaust before any mishaps.
 
I expected a response from the physicists and chemists on the forum!
The background;-
While fitting the heater and playing around with the fuel feed (referenced in another post), I used a container that had some (unrealised) water contamination in the fuel. There was steam in the exhaust very apparent outside but, alarmingly, water was escaping sideways from the flexible stainless hose. This hose was that supplied with the Chinaspascher. I assume that higher quality hoses may not suffer in the same fashion.
In any case, I have never felt comfortable making connection to the exhaust outlet stub using a compression clamp even a high torque wire based one.
Consequently, I have produced a rigid connection scheme.
For the benefit of others, it is possible to thread the exhaust outlet stub 1" UNF. This thread was chosen after exhaustive searching through my fairly complete selection. A BSP thread would have been far preferable but no size would fit. Metric 24mm suits but 3mm pitch it too coarse and, although I had 24X1, 24X1.5 and 24X2 dies, I don't have (probably can't find:)) matching taps.
To connect to the rigid stainless pipe leading to the transom outlet, I made a convertor from a piece of 40mm square stainless threaded internally to 1" UNF converting to 3/4" BSP.
1" OD stainless tube is not best choice for 3/4 BSP but with tape and sealant it will serve.
 
All that effort to get a good seal on the outlet and you are using the crappy van exhaust!
They can get that hot - but I don't think if its running optimally it should get that hot (you are just wasting fuel heating the exhaust).
 
Graham_Wright said:
There was steam in the exhaust very apparent outside but, alarmingly, water was escaping sideways from the flexible stainless hose. This hose was that supplied with the Chinaspascher. I assume that higher quality hoses may not suffer in the same fashion.
Click to expand...

In which case the hose is dangerous, unfit for purpose and should be replaced a.s.a.p. All the advice, even from the enthusiasts for these Chinese heaters, says bin the Chinese exhaust hose, silencer and other fittings, and just don't even think about fitting them.

The hose on my ancient Eber does get v hot, but not red hot.

Graham_Wright said:
In any case, I have never felt comfortable making connection to the exhaust outlet stub using a compression clamp even a high torque wire based one.
Consequently, I have produced a rigid connection scheme.
Click to expand...

Fitting the exhaust hose to the stub shouldn't require the specialist parts and lengths that you've gone to. I have to wonder whether the stub and/or pipe you have are the correct dimensions.

I've not done it myself (yet!), but the advice, as I recall it, in a video [link provided in later post below] from Owen Cox, who supplies and installs Autoterm (formerly Planar) heaters is to cut a short pair of slots lengthways in the end of the flexible hose (this allows it to deform), put exhaust sealant around the outside of the stub (not the inside of the pipe, as any excess will be pushed into and can partially block the pipe), push hose on then tighten with a proper, good quality, hose clamp.
 
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LittleSister said:
I have to wonder whether the stub and/or pipe you have are the correct dimensions.
Click to expand...
The stub is an integral part of the casting so not easily susceptible to variation.
There have been cautions expressed about condensation in exhausts. I think a solid thick walled tube is likely to last longer than a convoluted hose!
I am very happy with. my solution and, if others wish to take advantage of my experience, the information is available.
 
Graham_Wright said:
I think a solid thick walled tube is likely to last longer than a convoluted hose!
Click to expand...

Ah, I had misinterpreted your 'rigid connection scheme' as relating only to connections at either end.

I am glad you now have a set up you are comfortable with, but while any exhaust system will be subject to condensation, I am not aware of any general problem with decent quality stainless exhaust hose having an unduly limited life. The one on my boat appears to have been there many years.
 
I think a solid thick walled tube is likely to last longer than a convoluted hose!
Click to expand...
It wasn't clear in your original post that you'd replaced that whole exhaust with solid walled pipe. Does that mean you've lost all flexibility? if the exhaust is getting red hot is there an expansion/contraction issue with solid pipe?
 
ylop said:
It wasn't clear in your original post that you'd replaced that whole exhaust with solid walled pipe. Does that mean you've lost all flexibility? if the exhaust is getting red hot is there an expansion/contraction issue with solid pipe?
Click to expand...
No, The heater is supported on two hangers with a small amount of freedom of movement.
C of E for stainless is ~9 X 10-6 mm/mm per °C.
300 X 9X10-6 X200=around half a mm.
 
Here's a link to the video I mentioned in Post #6 above which shows how best to fit the flexible stainless exhaust hose to the ports on the heater, silencer, through-hull fitting, etc. Here he's installing one on a van, but he specifically mentions the difference (i.e. exhaust sealant) if doing a marine installation.

This is part of a long video which provides helpful guidance on various aspects of fitting this type of heater (albeit focused in this instance on a van installation), but I've set the link to start on the bit about exhaust hose.

Might be useful for others reading this thread, though I now know this is not relevant to the OP.

 
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