Type of stopcock

[cineko]

I have looked all over the forums but cannot find a definitive answer to this.
I employed a poor plumber who has replaced the stopcock in a first floor flat with a too small 'ball' type lever valve - similar to an appliance valve.
It is not 'full bore' (15mm pipe) and so flow is not great with 2 taps turned on.
I wanted to replace it - but with what?
The property has a stopcock in the street that shuts off ground floor and first floor flats together.
This small lever valve under the sink is the only means of shutoff to the first floor flat.
My main question is - should it be replaced with a traditional t-handle type stopcock - and would that prevent backflow under negative pressure conditions or can it be a larger bore lever valve (and would that also need a non return valve added as well)?

My concern is that when I had the water to both properties turned off (for other work) I could hear water from my pipes in the first floor draining down to the flat below when they opened their taps!

Is there something inherent in the design of a normal stopcock to prevent backflow - the arrangement of the washer perhaps?

Sorry I know from reading the forums that this question crops up regularly but I can't find the definitive answer I'm looking for.
Thanks!

 

[powell30]

You need to replace the ball valve with a bs1010 stop tap/cock. And fit a check valve on the run that supplies upstairs.

You should really provide a seperate supply to the individual ie t off main stop tap and then provide individual stop cocks for each property.....i assume water rates rather than a meter is the method of charging......otherwise one or other of the tennants is paying towards the others bill!

 

[cineko]

Thanks powell30 that's great info - of course I have more questions though!

To clarify a little I own both ground floor and first floor flats and yes they are both on water rates rather than meters.
There is a second stopcock inside the ground floor flat and I had always assumed this turned off the ground floor only - but I think I need to get the tenant to check if it is actually feeding the first floor as well.

I appreciate what you are saying about a BS stopcock and non-return valve and I think I'll do it the way you suggest. Does the non-return check valve have to come after the stopcock or is that academic? Does it need a check valve because it's first floor or because it is potentially connected to the same supply as downstairs?

Thanks for any further advice.

 

[ChrisR]

To comply with the regs each "dwelling" needs a double check valve.
The first tap into the property needs to be a screwdown valve, like a stopcock to BS but your valve could be a full flow ball valve, which would have less resistance.
After that would go the dcv, which would have a LOT of resistance! You could use a 22mm one with fitting reducers, to reduce the resistance. After that a drain cock would be appropriate.
Old stop cocks used to have a loose "jumper" which prevented backflow, but new ones have been "pinned" for decades now.