Rotary roof vents?

Hi all,
Does anyone here have any personal experience of those rotating roof vents you often see on dog patrol and other 'service' cars and vans
please?
I was wondering if one might help remove any fumes (fuel / wood treatments etc) from the back of a van, mainly when parked up?
The van in question has a full steel bulkhead and the fumes tend to clear pretty quickly as soon as the cabin blower is fired up (it's always on speed 1 at least) and I imagine these roof vents don't work (as well?) if there is no breeze etc.
So, are they quiet (given this is a van <g>), do they work worth the effort installing one and how long do they (bearings etc) typically last?
Is there a good brand that is the one those in the know fit?
Cheers, T i m
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On 4/18/2017 11:15 AM, T i m wrote:

I have one in a horse-box. I don't think it normally windmills much when not driving (although the bearing friction is pretty low). Mine was about £60 iirc. Easy enough to fit. It looks fairly robust, don't recall the make. Google suggests you can also get electrically driven ones. Maybe you could fit a computer fan to extract from the load space.
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On Thu, 20 Apr 2017 20:20:18 +0100, newshound

<snips>

I thought they were normally open at the top at the back but I guess you must also be able to shut them up completely.

Understood. Even if it didn't spin, I assume it would still act a bit like an extractor (venturi effect)?

I'd seen some for around £75 so they may not have been overpriced.

I was concerned about the idea of cutting a hole in the roof of the van but as the van is quite tall and old ... it wouldn't really matter if you we had to remove it and blank it off sometime.

I would imaging they would need to be fairly tough.

Np.

(Also) solar powered might be cool (if good enough quality panel) as it's likely to be most needed when it's hot.

Good idea and we could but unless we get a solar solution I wouldn't really like to trust it not flattening the battery etc (and it wouldn't really be needed when the van was occupied / running).
I don't suppose you could tell how effective it was unless you fitted one to solve a problem and it did? ;-)
Cheers, T i m
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On 4/20/2017 10:59 PM, T i m wrote:

Trailers are like that, lorries normally not. But this is a 3.5 ton Renault Master van conversion anyway.

Mine is a hi-roof version, the roof is plastic and therefore not really structural. Easy enough to blank off if you are not too worried about aesthetics.

Mine came with two "flip up" type caravan vents / skylights about a foot square. I didn't think the ventilation was all that good when driving. I havn't done any quantitative tests but I reckon the spinning one has definitely improved it.

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On Fri, 21 Apr 2017 00:25:15 +0100, newshound

Ah. ;-)

<snip>

Our folding caravan has one of those.

I guess it depends if they were the hinge up design and which way they faced and if you had the up when driving.

Cool. Thanks for the feedback.
Cheers, T i m
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On 4/21/2017 9:35 AM, T i m wrote:

Mine have a link each side, and pop up a couple of inches with the skylight remaining parallel with the roof when activated. So there is neither a "ram" nor a "venturi" effect, whereas the fan spins and provides directional flow (but not sure whether it blows or sucks).

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On Fri, 21 Apr 2017 17:44:36 +0100, newshound

That was my though. ;-)

I think that because it's 'driven' by the wind and with heat rising etc I think it's logical to assume that it sucks?
That said, I'm not sure I can quite get my head around the difference in functionality between it being spun (breeze / vehicle movement) and when it's on the overrun etc.
Irrespective, they obviously work so ... ;-)
Cheers, T i m
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On 22/04/2017 11:19, T i m wrote:

throws the air out with centrifugal force.
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On Sun, 23 Apr 2017 17:35:28 +0100, critcher

Interesting. Can you expand on that (I understand the concept of cetri-fugal/petal forces but not how they would apply with such a machine).
Cheers, T i m
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