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Author Topic: head pipe size? hot water pressure!!  (Read 2535 times)

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Offline myles

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head pipe size? hot water pressure!!
« on: March 30, 2014, 10:55:26 PM »
Hey all,
           I have replaced all of my hot water pipes (were galv/steel) with pb 15mm. Got rid of the head tank, replacing it with a pressure valve below the cylinder. all is working fine, twice the pressure already.

I am wondering what size my head pipe should be though. it is 20mm  up to 3 meters (original plumbing). my h/c has a 7.2 max head. i had 1m of 15mm pipe so i added that to it which made a bit of a difference. 

My question is would 20mm be better pressure wise than 15mm or dose it not make a diff?

Also 7.2m is really high. i have herd of pressure valves for the header pipe to simulate the pressure, do these work?

 cheers                      MK

Linkback: https://www.plumbers.nz/q-and-a-hot-water-cylinders/44/head-pipe-size-hot-water-pressure/1653/

Offline myles

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Re: head pipe size? hot water pressure!!
« Reply #1 on: March 30, 2014, 11:04:13 PM »
EDIT               The 1m by 15mm pipe i added to header was copper.

Offline robbo

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Re: head pipe size? hot water pressure!!
« Reply #2 on: March 31, 2014, 09:01:28 AM »

hi guys/Myles, the exhaust from the cylinder should be 20mm you need to change it. The difference between 15mm and 20mm pipe as far as pressure is concerned is that the pressure is the same as it is controlled by the atmosphere the only difference between the two is the volume of water that can pass through the pipe which will be more using 20mm.  You can install a pressure relief valve to replace the exhaust going through the roof which is a spring loaded device set to a certain pressure, can only be used on a system that does not have 'an uncontrolled heat source`(wetback etc.),hope this helps,cheers 

Offline robbo

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Re: head pipe size? hot water pressure!!
« Reply #3 on: March 31, 2014, 09:10:48 AM »
hi guys/Myles, (I have replaced all of my hot water pipes (were galv/steel) with pb 15mm) i presume you mean Polybuteline as PB could be confusing for the lay person as the chemical symbol for lead is pb (plumbum) lol,cheers

Offline myles

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Re: head pipe size? hot water pressure!!
« Reply #4 on: April 12, 2014, 03:49:53 PM »
cheers robbo yip i did mean polybuteline not lead.  The hot water cylinder is on coal range wet back, so wont be able to go down those roads then (pressure valve). cool thats what i thought about the header pipe size, will be changing it asap.

The hotwater cylinder has a head hight of 7.5 meters. Is this from the ground, pressure reducing valve (under the tank) or the bottom or top of the hot water cylinder?

Also when installing these set ups what height would a plumber normaly go to on average? the full 7.5 is rather high.

cheers          MK

 

Offline robbo

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Re: head pipe size? hot water pressure!!
« Reply #5 on: April 12, 2014, 05:07:08 PM »
hi guys/Myles, yeah the pb/lead was a bit of a joke, if you have a low pressure cylinder it will be rated to 25ft/7.6mtr head only, you may damage it if you increase pressure too much more. Head is measured from pressure valve to top of exhaust pipe,cheers

Offline integrated

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Re: head pipe size? hot water pressure!!
« Reply #6 on: April 12, 2014, 05:36:53 PM »
hi guys/Myles, yeah the pb/lead was a bit of a joke, if you have a low pressure cylinder it will be rated to 25ft/7.6mtr head only, you may damage it if you increase pressure too much more. Head is measured from pressure valve to top of exhaust pipe,cheers



this is true however you would only want to have 7.6m head acting on the base of the cylinder as that will be what it's max working pressure is - standing water level should be measured from base of cylinder if the pressure reducing valve is below the significantly below the hwc

Offline myles

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Re: head pipe size? hot water pressure!!
« Reply #7 on: April 12, 2014, 10:56:28 PM »
The pressure reducing valve is only around 20cm under the hwc, so ill just go from that point. I was thinking im going to go around 6 meters then i know its not going to put excessive pressure on hwc.


thanks for the help  ;D.   MK



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