How to improve air extraction system

[ahlondon]

I bought a house made in the 70s and just the top floor bathroom had mechanical air extraction via a vertical pipe through to the roof.

During renovation, I extended the pipe using underground brown pipe and fittings to allow for air extraction from:

Ground floor shower bathroom (centrifugal 10m run capable) and kitchen hood extractor
First floor WC toilet
Top floor bathroom and newly added ensuite bathroom

Extraction seems to be effective enough but the issue is that despite backdraught shutters on all units, the kitchen smells flow through to the first and top floor extractors despite it being a straight run to the top. An Equal Junction 110mm 45° Triple was used to connect the first and top floor vents, so the ground floor air to somehow still finding it easy enough to push downward 45°. What can I adjust to improve this system that already works pretty good? I can try to upload a diagram if that helps! Could it be that kitchen smells are so potent that the slight smell coming through is to be expected given the backdraught can't block it all out? I can't tell if moist air is also leaking from ground floor to other extractors...

Probably irrelevant but worth mentioning I have a condensate trap after the ground floor extraction and another after the top floor.

 

[Deluks]

Lay off the curries and kippers.


Are you pulling the air out from the top or pushing it out from the bottom?

 

[ahlondon]

Lay off the curries and kippers.


Are you pulling the air out from the top or pushing it out from the bottom?

Pushing. Each room mentioned has mechanical extraction

 

[Deluks]

Not an expert, but I would think that the fans would need to be linked so that they all kick in at the same time.
Or just have a single powerful fan at the end of run pulling the air through the duct.

Anyway, I've just noticed this is in the roofing forum.
Probably not the best place to ask the question.