The use and indstallation of a durgo valve

I had a bathroom installer tell me that I could get rid of the soil pipe that runs through my barthroom by fitting a durgo valve.
The soil pipe rises from the downstairs toilet and the toilet in the bathroom is connected to the 4 inch pipe as it passes throught the bathroom continuing up through the empty loft and out through roof.
I want to fit units at low level in bathroom and want to remove this intrusive pipe to below the granite worktop which will hold a counter top basin.
My plumber who is a friend tells me now that this is not allowed as the soil pipe has to be vented through the roof in all cases telling me its only for use when you install say a loft conversion and then its for capping the 4 inch pipe that is conected into the same pipe above ceiling.
Can anyone please clarify if I can install this unit i have bought frtom Screwfix or bin it

Reply from John to Richard
Many Thanks for your fast reply
So maybe this would help if I placed a narrow cupboard on the work top to conceal the durgo valve just above the overflow of the overflow of the washbasin.
The other way would be to divert the soil pipe below the work top through to the airing and boiler cupboard and reconecting to the original soil pipe in the loft.
I think this could be done using 45 deg bends or would 90 deg be ok for this change of route.
I am new to this site and cant see how to answer you reply but if poissible is there a telephne # I could speak to you about this on
Many Thanks John

Your plumber friend is wrong; you can install a Durgo (AAAV) on a stub stack to provide negative pressure venting but only if the foul drain system has another open vent stack to allow for positive pressure ventilation. The valve must be fitted above the highest flood level (overflow); this is usually the hand wash basin so you may not get it low enough to loose it under a vanity counter top anyway. It must be in a ventillated enclosure & accessible for maintenance.

If the bathroom has an outside wall you could run the stack out through that and up past the guttering.

Hi Richard thanks for the reply.
I did not know till now how to post a reply please see my reply which I added to my first question.
Maybe on second thoughts I wiould be best to box the pipe in as its near the corner anyway and then place a cuboard over it so it runs through it and tile the visible part above the cupboard as will not get one that goes full height from my suppliers Howdens
John