Is an air admittance valve required in this circumstance?

4 Feb 2021
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United Kingdom
I've been asked to fix a leak coming from some strap on bosses and an air admittance valve (as you can see in the picture). It's not been done right and I will be replacing everything in the photo (above the soil pipe elbow). Afterwards everything will be boxed in.
The two grey 40mm solvent pipes are connected to two separate macerators (for a kitchen sink and a toilet/basin in a converted cellar).
There is a separate primary soil stack connected to the drain (which goes through the property's roof with a cowl).
My question is whether an air admittance valve is required at all? I can't imagine much negative pressure would be generated by a couple of 40mm pipes discharging into a 110mm soil pipe, but even there was, I don't think this could cause any problems. (these pipes come from the floor and go up to the ceiling, so there is no way to suck water out of those pipes).
I'm just not sure if I will be breaking any regulations by not having an AAV?
Any opinions/advice would be greatly appreciated.


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