Shock arrestors

[kozak1968]

Does anyone know if there is a calculation for fitting a shock arrestor to the incoming main to a boiler. All I can find is that a shock arrestor/ expansion should be fitted if a back flow prevention device is fitted to the main, ie a double check valve or water meter.There is nothing about the minimum length of pipe or volume of water required to take up the expansion from a combi boiler. I'm sure someone will point me in the right direction.... Thanks.

 

[lame plumber]

what ever the MFIs say, I do

 

[kozak1968]

So basically fit one or you warranties void.......

 

[lame plumber]

if the manufacturer advices one if pressure is high or non return valve fitted then you fit it, or as you say ... nil warranty

 

[joni os]

Intriguing question, those of us around before water meters are inclined to think of a supply through open stopcock all the way back to the water tower. In reality an anti backflow device is usually fitted at boundary even for households who opt for a non meter account.
The volume effect is offset to some degree by the thermal expansion of the pipes through which the water flows and a diversity principle, similar to electrics, may be appropriate.
Meanwhile, one is better than none. I suspect many appliance is protected by a dripping tap.
Without wanting to limit discussion. I would also consider an unvented DHW cylinder may offer additional protection.

 

[Nostrum]

I spec them on every combi regardless of what the MI say. For the sake of a small cost it saves any potential damage in the future. Plus if you went to the extent of figuring it out (if even realistically possible) , who is to say it wouldnt be modified in a years time by some other plumbing works.