Technical question (my lecturer couldn't answer it!)

[chrishutt]

That's impressive evidence...However, the 11mm thickness of steel relates to a cylinder with an overall diameter of say 2+ metres, so scaling it down to a cylinder diameter of say 400mm, that would be equivalent to a thickness of say 2mm?

For comparison, an OSO cylinder has a wall thickness of 1.35mm but that's stainless steel (F18MT) so a good deal stronger in compression than mild steel (?). OSOs are rated at 8 Bar (120 psi) but factory tested to 16 Bar.

On balance, I think you win.

 

[micky p]

Is it illegal to have a pressure washer connected directly to the mains, or is it OK as it only has a low flow rate?

it is fine to have a pressure washer connected to the mains as long as it is connected via a double check valve bib tap.

Thanks, I'll have to look into buying one afaik my current bib tap doesn't have a double non-return in it, its been installed for years now. I take it I am allowed to install a check valve (or would it be two? can you get double?) before the tap instead?

you can get inline double check valves but it might be cheaper just to swap the bib tap for a double check valve one. single check valve is not suitable.

 

[Spark123]

The local shop only has single check valve bib-taps, says anti-syphon on the packet but as I take it I need a double check valve I'll wait until I'm near plumbcentre next. Thanks for the reply.

Reading the above I take it a Calorifier is the proper name for one of these on the top left hand side of this pic, what looks similar to a cylinder but with a water heat exchanger?:

I take it the one mentioned in doitalls post is probably quite a bit bigger but the same principal, or have I got it completely wrong!!

So why do some manufacturers not bother with AVVs?

What is an AVV? anti-vacuum-valve at a guess??

 

[towman]

All this talk of double check valves etc has stirred a faint memory that somewhere in the regs ts says that double check valves should be fitted at the mains stopcock? I know that not many people do have these fitted as it's probably a fairly recent (2000?) reg - but it does solve a lot of problems!!

 

[Agile]

I have a feint recollection that early instructions ( 20 years ago ) on how a water meter was fitted showed a double check valve.

There were isolating valves either side and drain off cocks.

I dont think there is any requirement for a check valve at the stop cock ( yet )

Tony

 

[ChrisR]

You certainly need a double check valve just after the stop cock coming into the house for new installations. Part of the Water Regs(Water Fittings) Regulations.

 

[towman]

So I was part right then

Now all that's needed is a definition of a new installation - I bunged one in when I renewed my water system a couple of years ago - just to be on the safe side. As it's a mains water system throughtout I also put single (or doubles depending on what was in my spares box!) check valves before the WC cisterns and external bib taps.

 

[ChrisR]

If you have a new supply from the mains, or a replacement (plastic for lead, say) they won't connect you up if you don't have a DCV. First thng they look for when they do the "Water Regs" inspection.

 

[Agile]

You dont need a check valve on a connection to a float valve but you DO need an isolating valve.

You need an isolating valve AND a double check valve indoors on a bib tap ( before Chris complains, thats at a domestic property! A commercial property bib tap should not be fed directly from the mains supply at all. Cat 5 liquids etc.)

Tony

 

[towman]

I thought you DID need check valves on mains supply to a WC cistern float valve? I'm sure I remember seeing that somewhere in the Regs, or a section from the regs - possibly WRC site? I've got them anyway - and isolating valves - and they're even labelled!

 

[Nige F]

I think that many of you should be taking theWater Regulations course!

Onetap has explained some of the health reasons for pumping from the mains to be prohibited.

The simple answer is that it is not permitted. ( Thats a full stop! )

As far as college lecturers are concerned, they are often second rate plumbers who have to teach because they cannot hold their own doing practical work.

They have almost enough knowledge to teach the course material but often no more. Why would they spend house a week for about £15 per hour when they could be earning twice that doing a real job.

Ask them a question off subject and its unlikely that they will know the answer.

Another reason is that the shower INLET pressure maximum is usually less that the mains pressure so you could damage a pump seal.

Tony

They might also be raspberry ripples who can`t physically do the job any longer...........I am .I have(taught)..and I guess your firm doesn`t display the "positive about disabled" logo, Tone?..........I sincerely wish you stay agile until you retire @ least - Bitter? NO twisted -2 fingers and a foot are