Part 1 or Part 2
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Get a copy of the Water Regulation Guide book from WRAS - this is the bible for plumbing regulations.
Generally Part 1 valves may allow backflow unless a double check valve is fiited upstream, Part 2 valves provide an air gap between the water level and the discharge point and therfore reduced chance of a backflow.
Although Part 1 valves are available, use a Part 2 valve as no need for check valves. Float level adjustment is also easier.
Incidently there are also Part 3 and Part 4 valves.
Generally Part 1 valves may allow backflow unless a double check valve is fiited upstream, Part 2 valves provide an air gap between the water level and the discharge point and therfore reduced chance of a backflow.
Although Part 1 valves are available, use a Part 2 valve as no need for check valves. Float level adjustment is also easier.
Incidently there are also Part 3 and Part 4 valves.
At first sight that looks quite correct and may well be the "official line".
In reality a Part II float valve has little more ability to prevent backflow that a Part I float valve.
Both valves will become flooded if either they leak or external factors drive the water level up over the valve and both types could then equally give rise to backflow.
The primary difference is the Pt I discharges from below the axis and the Pt II from just above the axis. In addition the Pt II has an adjustable float position and that should ease setting the water level in the cistern correctly. The Pt I can also be adjusted by the simple means of bending the shaft over the knee.
As always the reality is that a bent Pt I will stay in adjustment for ever but a Pt II can fail to hold its setting point because the clamping screw is often not firmly tightened and serious consequences arise if the float is free to rise to the top of the adjustment.
Another aspect is the flow rate and the overflow system. If there is no flow out of the cistern and the valve is held down then the level should be restrained by the overflow to prevent the valve from being flooded and the maximum flow rate into the cistern should not exceed what the overflow can discharge.
I assume that you are asking as part of training and you are probably only needing to get simple "tick box" basic knowledge in which case forget what I have said.
On the other hand if you want to extend your knowledge so that you can challenge your Lecturer ( or even Softus ) then remember this here!
Tony
In reality a Part II float valve has little more ability to prevent backflow that a Part I float valve.
Both valves will become flooded if either they leak or external factors drive the water level up over the valve and both types could then equally give rise to backflow.
The primary difference is the Pt I discharges from below the axis and the Pt II from just above the axis. In addition the Pt II has an adjustable float position and that should ease setting the water level in the cistern correctly. The Pt I can also be adjusted by the simple means of bending the shaft over the knee.
As always the reality is that a bent Pt I will stay in adjustment for ever but a Pt II can fail to hold its setting point because the clamping screw is often not firmly tightened and serious consequences arise if the float is free to rise to the top of the adjustment.
Another aspect is the flow rate and the overflow system. If there is no flow out of the cistern and the valve is held down then the level should be restrained by the overflow to prevent the valve from being flooded and the maximum flow rate into the cistern should not exceed what the overflow can discharge.
I assume that you are asking as part of training and you are probably only needing to get simple "tick box" basic knowledge in which case forget what I have said.
On the other hand if you want to extend your knowledge so that you can challenge your Lecturer ( or even Softus ) then remember this here!
Tony
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I went to buy a 3/4" part 2 or higher recently and was offered only a part 1. The only place ( I think, though may be wrong) that you can use a part 1 on the mains, is on a wc. That's because the cistern water is low risk, as there's such a high protection against backflow up from the pan .
(Until some prat puts a "bloo" in it of course.)
Part 2 valves rely (in the spec) on there being an effective overflow to prevent water getting high enough to enter the top of the valve. Obviously silly!
I pressed the "where is apart 1 ok" question when I did the water regs course some years ago. Nobody was very sure! You can of course use then on secondary cisterns (ie not mains fed).
It has been said here that you can use them on mains fed CH headers, which seems daft if you can't use them in DHW cisterns with bylaw 30 / reg 16 kits. CH water is cat 3 iirc. Justification was that the ch water is not potable -which misses the point.
(Until some prat puts a "bloo" in it of course.)
Part 2 valves rely (in the spec) on there being an effective overflow to prevent water getting high enough to enter the top of the valve. Obviously silly!
I pressed the "where is apart 1 ok" question when I did the water regs course some years ago. Nobody was very sure! You can of course use then on secondary cisterns (ie not mains fed).
It has been said here that you can use them on mains fed CH headers, which seems daft if you can't use them in DHW cisterns with bylaw 30 / reg 16 kits. CH water is cat 3 iirc. Justification was that the ch water is not potable -which misses the point.
What about the screened overflow kits.
Whats the point in having 19mm overflow/warning pipework, a maximum screen hole size of 0.65mm and then not ensuring the flow rate is not de-minished.
I have yet to find a bylaw 30 kit where the manufacturer has incorporated a sufficiently large mesh not to severley reduce the flowrate through the overflow.
Some screens flow worse than a bit of 15mm copper.
Whats the point in having 19mm overflow/warning pipework, a maximum screen hole size of 0.65mm and then not ensuring the flow rate is not de-minished.
I have yet to find a bylaw 30 kit where the manufacturer has incorporated a sufficiently large mesh not to severley reduce the flowrate through the overflow.
Some screens flow worse than a bit of 15mm copper.
Thanks for all the replies. I have a leaking ball valve on a tank in the loft and called in to local merchants where I was asked whether I needed a part 1 or a part 2. I drew a diagram and got like for like ( part1), but my curiosity was aroused. It's the tank for the heating system. Judging by the posts I've got the wrong one so I'll swop it. Thanks again.
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Gasguru said:
But don't the water regs require you to notify the Authority 10 days before you install an appliance which takes more than 12 litre/minute from the public supply? In that case the overflow only has to flow 12 l/min, doesn't it?
Do what?
Your talking about pumps etc. or does meldrew notify every time he fits a tap.
Its doubtful if some of these screened overflows would cope with 5 litres a minute - and certainly not a failed float valve.
Your talking about pumps etc. or does meldrew notify every time he fits a tap.
Its doubtful if some of these screened overflows would cope with 5 litres a minute - and certainly not a failed float valve.
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