Shock Arrestors / Mains water supply - Best Practice?

[SirLancelot]

Exploratory discussion about best practice for the ordinary home & Water Shock Arrestors:


Standard 3 bedroom semi detached house, water meter is on pavement out front.

Blue pipe comes into the house under alleyway.

Where (and how many) shock arrestors should be fitted in an average home.

I know some boiler manufacturers need one installed close to the boiler. But thats not what i'm talking about

I'm talking about protecting the rest of the system for in houses where the piping is old (e.g mine is 25 years - Copper).

Do any UK regs mandate/recommend water shock arrestors in the average home?

If so, where in the system (other than near the boiler) should they be installed?

 

[Madrab]

Not needed and no, there are no regs that state arrestors should be used

Shock arrestors are mainly used where there may be sensitive components that could be damaged by hydraulic shock in the case of water hammer. The only other reason maybe where there is excessive mains pressure but that would usually be dealt with by a drop tight pressure reducing valve They are not designed to mask issues created by pipework and fittings that haven't been installed correctly, though that's one of the primary reasons they are used.

Properly clipped and maintained pipework and fittings shouldn't have any issue with dealing with anything that domestic mains can throw at it as most are spec'd up to at least 10bar, even at 25+ yrs

 

[RandomGrinch]

Properly clipped and maintained pipework and fittings shouldn't have any issue with dealing with anything that domestic mains can throw at it as most are spec'd up to at least 10bar, even at 25+ yrs

Yes, true.
However, in an old property, with unclipped pipes and unknown pipe runs, there may be a limit to how much investigation and invasive work someone wants to perform.
With the battle to gain A+ energy ratings, condenser washer dryers in particular, are notorious for their instantaneous intake solenoids cutting on and off the water continuously for hours on end; causing water hammer issues in homes that hadn't suffered from it previously.
It's not a great substitute for perfect pipework, but IMHO, local shock arresting of troublesome appliances can be worth considering.

 

[SirLancelot]

So for a good installation they shouldn't be needed (other than when specced by boiler manufacturers).

I have pipework that is 25 years old. The kitchen an bathroom taps are lever taps, so the cut off is quick.

What different types of shock arrestors would the community recommend. Where should I put it / them.

Would it make sense to put it near the mains house stop-cock, if I am looking to protect the entire infrastructure of the house?

 

[Madrab]

However, in an old property, with unclipped pipes and unknown pipe runs, there may be a limit to how much investigation and invasive work someone wants to perform.

Certainly not suggesting they shouldn't be used but IMO they should be considered a last resort as there are other ways to correct water hammer issues rather than using a component to supresses it.

I have pipework that is 25 years old. The kitchen an bathroom taps are lever taps, so the cut off is quick.

TBH as long as you don't have an issue with hammer then they are not needed. You would be adding a component onto a system that doesn't need it.

For the very reasons mentioned unfortunately I wouldn't be able to recommend a specific type as I haven't ever had the need to use them.

 

[Pete the Feet]

Some items can cause water hammer. If the water flow is suddenly interrupted such as a solenoid valve closing sharply this can cause it. Our previous washing machine was a culprit for this, as is the steam generator for the shower cubicle. I've tried numerous surge arrestors on the steam generator but non seem to last. The previous two were Sioux Chief arrestors. Neither lasted much over 12 months. Prior to that I tried Reliance surge arrestors. These were even worse.

 

[RandomGrinch]

Our previous washing machine was a culprit for this

A decent compromise for washers/driers with this problem, along with the shock arrestor, is to semi-close the isolator tap.
You may need to close it quite a way, but this doesn't really have any affect on the machines performance, other than a slightly longer fill time.

 

[Madrab]

Some items can cause water hammer. If the water flow is suddenly interrupted such as a solenoid valve closing sharply this can cause it.

I think it needs to be understood what water hammer is, most people I have asked believe it when there is a knocking noise from the pipework. That's only the outcome of water hammer - Water hammer is actually where there is relatively high mains water pressure and a quickly closing valve (electrical solenoids on WM's/DW's, CW cistern float valves, etc) creates a significant hydraulic shock wave that travels back down the pipework from the valve. That hydraulic shock will usually occur where those conditions exist but most people only know they have it when their pipework knocks. The key to avoiding it in the first place is correctly controlled and maintained mains water pressure, the use of check valves and properly installed pipework/fitting and fixtures that are WRAS approved.

Most pipework and fittings can absorb a level of hydraulic shock from a 3 bar mains to a certain degree and it's one of the reasons why all WRAS approved fittings and outlets etc are tested and passed at a min of 10bar.

The trouble starts when that shockwave hits unsecured pipework and inferior quality non WRAS approved fitting and fixtures where the mains pressure is uncontrolled and there's badly installed and supported pipework.