Plumbing Sizes - Is It Only Me?

Bustup15

Bustup15

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New to motorhomes 2019
Bought a motorised valve for waste tank.

Stamped as DN40

Spec reads: Connection: thread
Size: G1-1/2" DN40.


Off to Screwfix and pick up 40mm pipe and connectors but its way too big?

A 32mm - 40mm reducer fits perfectly for the valve and allows 40mm pipe connection.

How does that work and if I order a tank with 40mm straight outlet what am I going to get?
 
Lenny HB said:
Also 40mm German pipe is not the same size as 40mm UK pipe as I found out.
Click to expand...
Please explain. I thought mm were all part of that Johnny Foreigner nonsense!:giggle:
 
Podney said:
Please explain. I thought mm were all part of that Johnny Foreigner nonsense!:giggle:
Click to expand...
Fraction of a mil different, but the German ones from CAK Tanks and they fit fine, ones from the plumbers merchant don't.

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i think you will find that pipe sizes also differ from different manufacturers - its not just variations in different countries. 'old school' will suggest that tube is measured as an external diameter and pipe as internal diameter - when its an internal diameter, then the pipe wall thickness can make a difference - you would notice this when looking at push fit and pvc solvent weld waste pipe
 
I got my 40mm pipe from a local koi carp supplier and as you said, plumber's domestic waste pipe was nowhere near.
 
It’s no good buying 1 1/2 40mm waste pipe you need to get water pipe as that is 40mm od, I bought some from an irrigation firm
Glen Farrow in Spalding plus they keep all of the relevant fittings.
 
eddievanbitz said:
Did you know that you have to use a 13mm Spanner to do up a 8mm Nut?

So don‘t buy a bag of nuts looking at the spanner you’ve just used👍🏻
Click to expand...
Surely the 8mm nut is the thread size...therefore making it 8mm....however it has a 13mm hexagon on top so you do indeed need a 13mm spanner to tighten an 8mm nut
But yes eddievanbitz I do take your point and could be confusing to some...😎
 
eddievanbitz said:
Did you know that you have to use a 13mm Spanner to do up a 8mm Nut?

So don‘t buy a bag of nuts looking at the spanner you’ve just used👍🏻
Click to expand...
Nut (or bolt/stud) size is by the thread size, spanner size is by the 'across the flats' dimension and don't be fooled into thinking that all nuts with the same metric thread size have the same spanner size!
 
rod_vw said:
Nut (or bolt/stud) size is by the thread size, spanner size is by the 'across the flats' dimension and don't be fooled into thinking that all nuts with the same metric thread size have the same spanner size!
Click to expand...
Many countries use different standards, when using German made 8mm nuts use a German spanner, UK made use UK spanner and so on. Italian 8mm nuts have a different pitch. If 8mm nuts are used on some vehicles you need a 14mm across flats unless its UK made then the clearance needs to be in the spanner. The Americans are best left out. If I've got any of this the wrong way round your knuckles will tell you.

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ctc said:
Many countries use different standards, when using German made 8mm nuts use a German spanner, UK made use UK spanner and so on. Italian 8mm nuts have a different pitch. If 8mm nuts are used on some vehicles you need a 14mm across flats unless its UK made then the clearance needs to be in the spanner. The Americans are best left out. If I've got any of this the wrong way round your knuckles will tell you.
Click to expand...
Did you know that UNC and Whitworth are inter changeable up till half inch!!

7mm dia is rarely used and when it is it is normally metric fine!
 
eddievanbitz said:
Did you know that you have to use a 13mm Spanner to do up a 8mm Nut?

So don‘t buy a bag of nuts looking at the spanner you’ve just used👍🏻
Click to expand...
That is logical. Imperial spanners labelled with the across flats nut size used to follow the size stamp with "AF" until the Whit / BSF spanner labelling nonsense was no longer an issue. At least Metric spanners have always been labelled with the only important dimension - the jaw gap. Nuts across flats dimensions don't always relate to the thread size. But you of all people know all this anyway :roflmto: .

More seriously pipe and pipe thread designations don't follow any obvious logic particularly when Metric measurements are in the mix. Many "metric" components sold throughout the countries that have always been metric use BSP threads on their plumbing fittings. And there are metric pipe fittings that use metric thread forms. Throw in JIS and NPT to cause total confusion.
 
Back to pipe sizes!
40mm/1-1/2" Push fit pipe is different to the equivalent solvent weld pipe and some waste fittings that purport to be that size are different again.
I found that toolstation 40mm solvent weld access ends to be exactly the right thread for my 1-1/2" motorised valve (more by luck than judgement)
 
eddievanbitz said:
Did you know that UNC and Whitworth are inter changeable up till half inch!!

7mm dia is rarely used and when it is it is normally metric fine!
Click to expand...
The Watney Mann brewery used UNC & UNF on many of their machines, all supplied by Vickers.

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A place I used to work at had some old Whitworth nuts and bolts in the back of the stores, they were pre war stock and the hex sizes were a size bigger than the "modern" Whitworth ones we used, apparently they'd shaved down the size during the war to save material, a bit like they did with trouser turn ups !
I'm pretty sure BSP pipe threads are based on the Whitworth system too ?
 
Having worked in the water purification industry for many years, it's a real mess. We use a lot of ABS and PVC, 1/2" PVC pipe has an outside diameter of 21.4mm (almost 27/32") and the inner diameter is 14.2mm-21.7mm dependant on pressure rating. There are several manufacturers producing this size pipe to the standard size, but not all fittings are interchangeable, some tight some loose. Nightmare on site when repairing pipe work from cheap or unknown manufacturer.

If you really want a headache, start looking at stainless pipe work and flanges, I still use reference sites when specifying to avoid errors.
 
Fittings vary in size, quite a bit. I have over the years installed quite a bit of UPVC and PVC in aquariums, last system installed here took this lot:

Screenshot 2021-03-23 at 14.41.49.png


As such i realised that manufacturing tolerances are quite broad..... to say the least.

I now only buy ALL components from the same supplier for a complete install as i get fed up of bodging joints.

2 good and pretty consistent manufacturers are VDL (the best) and Comer (still very good). The trouble is we often over buy an odd joint, keep it of course and then on the next job end up with all sorts needing to be fitted together and the you realise that you've either got to sand down pipe to fit or have a dodgy joint due to a too thick glue seam...
 
berni109 said:
Back to pipe sizes!
40mm/1-1/2" Push fit pipe is different to the equivalent solvent weld pipe and some waste fittings that purport to be that size are different again.
I found that toolstation 40mm solvent weld access ends to be exactly the right thread for my 1-1/2" motorised valve (more by luck than judgement)
Click to expand...
Solvent weld end but is the right thread for your valve - how does that work 😳
 

Solvent Weld Access Plug 40mm Black​

From toolstation - unscrew the access cap and discard - screw fitting into valve.
Hth.
 
berni109 said:

Solvent Weld Access Plug 40mm Black​

From toolstation - unscrew the access cap and discard - screw fitting into valve.
Hth.
Click to expand...
Thanks - for that price will give it a go
 
rod_vw said:
Nut (or bolt/stud) size is by the thread size, spanner size is by the 'across the flats' dimension and don't be fooled into thinking that all nuts with the same metric thread size have the same spanner size!
Click to expand...
not strictly true, a 1/4 inch whitworth spanner relates to the thread size not the head size, it is much bigger than 1/4 inch across the flats !!
Just trying to confuse the issue even further. :giggle::giggle::giggle::giggle::giggle::giggle:
 
I recommend these people. https://www.plasticpipeshop.co.uk

I have bought a lot of fittings from them. They are happy to give advice and when I placed an order for various bits and pieces they actually rang me to tell me they weren't compatible. Thoroughly recommended

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