water stop and servicing valves

[long ironer]

Many thanks to posters for recent help on feed pipe positions for the new CW cistern. I have now got hold of a copy of the Water Regs Guide, hence another question.

What are the precise definitions of 'stop valve' and 'servicing valve' for the water regs purposes (they aren't defined, so far as I can see)?

IME 4 types of valve are on sale viz:

a. Brass units with tap style handles, sold as stop valves which screw down a washer like standard taps. I suspect these restrict flow diameter, but mains water pressure is such that it doesn't make much difference - is that right?

b. Gate valves, which IME allow sepage when closed once they are a year or two old, & SFAIUI are unsuitable for pressurised systems, but the gate valve opens to provide a clear straight through bore, that is full flow. Are these now obsolescent?

c. In-line units sold as service valves - usually with a chisel screw head for operation with a screwdriver. On these an internal ball valve is rotated by the screwdriver. Flow is usually restricted because the internal ball dia is usually less than the connecting Cu diameters. These appear to be suitable for normal domestic water temperatures and pressures. Valves for washing machine supply pipes seem to be a variant of this with a small lever for operation instead of a screw head.

d. Ball type valves operated by a lever. Otherwise similar in style to c, the ball diameter is larger allowing full flow at the connecting Cu diameter. What operational conditions are these suitable for?

So which of these 4 types are suitable for use as a stop valve, and which as service valves? Indeed what are the correct applications of the above valves?

A long time ago (mid 90s) a water board inspector told me that service valves had to be operated by a screwdriver. I can't see that in the regs, so is it still correct?

A problem I have is that ideally the cistern is on the low side, so I'd prefer to use full flow valves wherever possible to reduce pressure loss..

Any info much appreciated, TIA

[John Rumm]

Don't take this as a definitive answer, just the results of my experience with the things...

Not sure there is any real difference.

This is your traditional sstopcock type of tap. The do reduce flow a bit (and cause some water hammer) but, as you way with mains pressure not much of an issue. They are prone to seizing up if you open them hard against the end stop (always better to open fully and then close a half turn)

They can work on pressurised systems. They do have many limitations and are generally best avoided (they also have a habit of breaking internally such that the knob still spins by the valve does not actually move). However they are handy for where you want to regulate flow though (like balancing zones in a CH system).

You can get these in full bore as well. In fact it is often not worth buying anything other than full bore.

Yup. If not often used then they can get stiff due to scale in hard water areas.

I tend to use these (or the similar butterfly valves) as a general replacement for gate valves. Any place you need to provide a way of shutting off water for maintenance and pipework alteration.

The tap type is ok as a stop valve, but not usually used for a service valve.

Gate valves are best avoided unless you just want either a cheap temporary stop, or a way of regulating flow in a system.

Ball valves for pretty much every other application. I tend to use screwdriver operated ones where they are partially visible or you don't want or expect them to be used often (under sinks, drain point on the CH), and the leaver type for things like the feed from a cistern to a hot water cylinder, or the shut-off valves either side of a shower pump or in-line filter on a CH system.

Don't know.

This is for the fill to a toilet cistern or a main header tank? Toilet cistern I would use a screwdriver operated full bore ball valve. In a loft/airing cupboard then a leaver operated full bore ball valve.