Tap isolation and backflow prevention

[Merx]

Hi all. I'm a DIYer about to change an old bathroom sink for a new one. It's currently all done in 15mm copper with no isolating valves and plumbed straight into the taps without any flexi hoses or similar.

My questions are these:
1. I'm going to fit isolating valves, probably Pegler full-bore lever type. Is this the best idea?
2. Do I need some sort of check valve for backflow prevention or does the air gap from the tap to the basin suffice? If so, would this be fitted before the isolator on the supply side?
3. Is it a good idea (or even required) to fit some sort of drain cock after the isolating valve?
4. Due to the design of the monobloc I'll be using, I guess I'm limited to using flexi-hoses that are supplied with it. Can I do anything about the pressure drop associated with these hoses or use copper tails?

I've tried to search for these answers already in the forums (fora?), especially the drain cock bit, but not really come up with anything definitive.

Many thanks in advance for your help and the benefit of your experience. I could get a plumber in, but this seems pretty straightforward. I just want to do everything as would be expected by current regs.

 

[longdogs]

Hi

Lever type valves are great and easy to use but can be a bit difficult if in a confined space ie: behind a pedestal. For neatness I would normally fit these:

http://www.screwfix.com/p/15mm-full-bore-isolating-valve/46860

The gap between the tap and the basin prevents any backflow of waste water so that's fine.
Check valves should be fitted if the cold supply is from the mains and the hot from the cylinder as the pressures will be different.

No need for a drain cock as water can be drained from downstairs if required.

You shouldn't notice too much difference with the flexi tails, especially if you have a combi system, but I suppose you could always replace with copper tails if need be. take the tap to a plumbers merchant and they will give you the correct size.

 

[Merx]

Thanks for the reply. The cold is from the mains and the hot from the cylinder as you say so I shall fit check valves.

I should have pointed out that these taps will be on a downstairs bathroom, so would this mean I should fit drain cocks?

As the sink is downstairs, at least I'll have the head of the hot water cylinder. It's a 'normal' boiler system with header tank but the hot water flow to the adjacent utility room seems powerful enough to not worry about the flexi pipes.

Many thanks for your help, I will do this on the weekend.

 

[longdogs]

Thanks for the reply. The cold is from the mains and the hot from the cylinder as you say so I shall fit check valves.

I should have pointed out that these taps will be on a downstairs bathroom, so would this mean I should fit drain cocks?

As the sink is downstairs, at least I'll have the head of the hot water cylinder. It's a 'normal' boiler system with header tank but the hot water flow to the adjacent utility room seems powerful enough to not worry about the flexi pipes.

Many thanks for your help, I will do this on the weekend.

It would certainly be useful to fit drain valves.

 

[Whitespirit66]

Before rushing to replace standard, separate taps with a funky new monobloc, make sure any new tap is suitable for unbalanced supplies (mains C, gravity H) and low pressure hot.

Fit the wrong tap, and you could find that the hot flow is disappointing. You need to check that the head available from your hot supply is at least up to the minimum head required by any monobloc.