Cobbled together an air extraction system for the garage

[Gavin_d]

I used tapering plastic plant pots as reducers.just cut to size

That's a flipping good idea!

 

[DAPPH]

Put your fan inside or surround the fan with a plywood box / housing , make a hexagonal or octagonal lip of 2 x 2 wood round the 6 inch pipe hole , fit the pipe in , use some long wood screws to hold the tube in place then mastic it in place and let it cure over a few days before you spark up .

I did a similar thing but in reverse for a couple of flush to the ceiling bathroom & toilet room mounted extractor fans that then were piped off nearly 3 metres to the gable end and then out the cavity wall via a second " flange box ".

 

[CRS51]

Just out of interest a question for those who know,
I have a 150mm centrifugal extraction fan rated at 1090cu m per hr and lengths of 150mm smooth bore plastic pipe and bends etc for my extraction, now would the extraction rate be improved if I were to go down the Venturi extraction route ? And also by what kind of percentage increase if any there would be ?
Thanks in advance
Chris

 

[DAPPH]

I guess ... :-
Each bend will have some sort of resistance to air flow factor . A venturi is a massive restriction you could be losing suction or pressure if it is too restrictive.
Where you put the fan in the pipe work depend whether you are just pulling air , just pushing air or doing both so the extraction rate will be different for each case.

Putting a venturi in the system would to my thinking restrict the air flow .. all a venturi does is speed up the a pulled/pushed air flow as it passes through the venturi.
To keep the speed up the bore of the smaller pipe would have to be constant to have the higher air speed along the whole smaller pipe .

I suspect that the calculations for eh air speed through a venturi are very variable for such things as the shape of the venturi can vary tremendously . the deign of the fan will also have a bearing on it .
On engines we used to check the ignitions settings by measuring the depression in the inlet manifolds with a big 24 inch dia mercury filled vacuum gauge to get the magic figure as near to 21 inches of mercury depression for maximum air induction in a low compression petrol engine . . I suspect you'd find that way using a vacuum gauge will be much better than a complex theoretical calculation

It will be interesting to see how well my thinking stands up

 

[skotl]

Am I right in thinking that discussion of the venturi started with a concern that crud would get into the fan in my original, rather basic, setup?

If so, I can't help thinking that the complexity of the venturi solution outweighs the risk of damage to what was admittedly a pretty cheap (£30 second hand) fan in the first place. Or did I miss something?

 

[DAPPH]

You are spot on .

 

[skotl]

You are spot on .

Ah! OK - good

 

[T0rnado69]

sure works a treat that. nice one


plenty of sucking power with this one 8" 780 m3/h lol

ild be a little worried about having my hands and torch to close to the end of the pipe.

 

[CRB]

Am I right in thinking that discussion of the venturi started with a concern that crud would get into the fan in my original, rather basic, setup?

If so, I can't help thinking that the complexity of the venturi solution outweighs the risk of damage to what was admittedly a pretty cheap (£30 second hand) fan in the first place. Or did I miss something?

?Over thinking again?

With the fan inlne pulling, crud gets into the fan.
With the fan at the clean end, though still pushing, you need a 'venturi' connection to extract from the site. No crud.
Any bend will 'hurt' the throughput. 90* bends in square-section duct should have quarter-round vanes in them to help the movement.

You could always test both ways, using drainpipes or soil pipes.

 

[skotl]

I suspect the crud is a lot heavier than the air and, having to make it up a 4ft vertical / flexible duct then most will get deposited in the duct.

Anyways - I'm happy to run it for a while and if the motor lasts a year or two then for £30 that works for me!

 

[johnakay]

I've got a extraction fan from a large cooker hood with all the fittings(no hood just the motor) inc 3 pin plug .
free to pick up from stockton.

 

[Gavin_d]

Here is the one I've done. The blower is now in the loft area with a on off switch wired I to workshop.

 

[skotl]

Here is the one I've done. The blower is now in the loft area with a on off switch wired I to workshop.

Nice. Do you have a link for the flexible hose? Seems a lot more manageable than plastic tumble drier hose.

 

[Gavin_d]

Here is the item number

111298262574

 

[CRB]

Like the 'stiff enough to be flexible though'. I have some camper heater duct which does not bend too easily and some cooker hood duct which will not point in the direction it is meant to.

 

[Gavin_d]

It's not that rigid. I often need to clamp it in place.Main reason was so I could push it back towards the roof to keep it out of the way when needed.

 

[skotl]

A belated update...

I bought a Nederman extraction arm at auction for £45 (yep, well chuffed- several hundred quid second-hand);

I couldn't get a good fit with the extraction system that I'd built so I've bought some additional plumbing and am going to move the motor to the business end of the nederman hose.
More info, pics and vids soon

 

[skotl]

Got the nederman inserted into the garage today!

Took a bit of fettling - I suspect these things are intended for slightly larger work spaces

I ended up strapping it to a shelf, with plenty of steel bracing, then took the motor out of the roof space, cut a hole in the shelf, and mounted it vertically close to the hose.
A 150mm to 100mm adapter and some aircon tape later and job's a good 'un

 

[AndyStobbs]

I can see a 'post up your extraction' thread coming on,

 

[DAPPH]

Don't get too close to the extractor unit lest you get sucked off big time with the torch in your hand .