The question regards a plumbing valve with 'stop' incorporated.
From my experience 'Stop' means - non return valve.
A valve with a loose washer, that will seal 'techinally' to prevent backflow.
Most of our water meter valves are 1/4 turn, hence the requirement for a dual check backflow valve.
This is to prevent the water from a property entering the mains, if the mains are switched off for any reason.
Not sure what Cat 3 & Cat 5 are.
In the course of my investigations, I have come across about this. I know that others have already explained this and I wish to add the details that I also found as further information.
I read (on this forum) that a water meter had it's own backflow prevention, therefore a lever ball valve was OK internally.
I would refer again to the WRAS FAQs which answers about backflow:
WRAS Installation FAQs
The very first section under "Backflow prevention".
The first question "How can I protect from Backflow" has a table, which lists the Fluid Categories - this is what Chris is referring to regarding cat 3 & cat 5.
You'll also see a question "When do I need to install wholesite protection":
Q. WHEN DO I NEED TO INSTALL WHOLESITE PROTECTION?
The Water Supply (Water Fittings) Regulations and Scottish Water Byelaws only specify two situations where wholesite protection may be required or considered necessary.
1. To prevent backflow between separately occupied premises, an example could be in blocks of flats or other buildings of multipleoccupancy such industrial units or shopping arcade.
2. A water supplier may consider additional protection is needed for the whole or part of buildings where there is an increased risk of backflow occurring.
Your local water supplier is best placed to advise on the situations which may require additional protection.
This concurs with what is stated by the earlier posters in this thread and
this forum post from Mike Jackson:
Backflow protection is not required in a normal domestic house at the point of entry, point of use protection is required. In multi occupancy properties with a single rising main where backflow could occur from higher to lower properties protection is required at all but the lowest property.
Although a loose jumper stop tap will function as a primitive back check valve it is not recognised as such within the water regulations.
Finally, what I hope might make things clearer, as it goes into more detail, is the Arrow Valves technical guidance I linked to previously:
https://www.arrowvalves.co.uk/media/wysiwyg/pdfs/Water_Regs_Tutorial_9-Isolating_Valves.pdf
See page 4 (or the summary on page 5 if you want a quick answer).
I just thought I'd share the links and information I had already come across and hope this helps.
I'm grateful to you guys for trying to explain what WRAS means by their answer to a "higher performance" requirement of a lever ball valve for a mains stop valve. I too had compared the Pegler stopcock technical specs with their lever ball valve. I wondered if it was to do with operating pressure - but that is the same also.
If I may ask please some further questions:
1. DZR Brass valves: I live in a hard water area, are these suitable? Will it make a difference? Would it be better than the common chrome plated ones?
2.
Some lever ball valves have an "anti blow out stem" is this a feature one particularly wants to have?
3. The Arrow Valves Lever Ball valve, as explained on page 2 of their technical guide, has a serviceable PTFE spindle seal. The gland nut can be tightened if it leaks and the PTFE spindle can be serviced etc. They designed it this way because they say a number of local water authorities want serviceable spindles and it can also be used for oil as it has no O-ring.
I'm just wondering if it could be a prone to leaking like the old brass stopcock with the gland nut and all that. Interested in your thoughts please?
Thank you very much.