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sxz



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Topic # 150356 20-Jul-2014 00:02
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We run a low pressure hot water cylinder. Supposedly 60%+ of nz does. Mains pressure cold runs through a pressure limiting valve into the tank, pushing hot water into the house at the pressure of that valve.

Due to thermal expansion we have an overflow pipe sticking straight into the sky, so if pressure gets too high it releases by bubbling over, no damage done.

Our pressure is on the poor side. My question is, if I install a pressure relief valve that stimulates another 3.6m of pipe on the roof (or if I install another 3.6m of pipe on the roof), and i dial up the pressure of the cold water pressure reducing valve so the internal task pressure is higher, will this likely damage my cylinder or should it have some in built tolerances?

Methven seem to suggest it as an option here, bullet point 6, page 1:

https://www.google.co.nz/url?sa=t&source=web&rct=j&ei=e1nKU6vFHouBywPDiIGoAw&url=http://www.methven.com/nz/specialist-brand/nefa/pressure-and-vacuum-relief--valve/install-sheet/285003.pdf&cd=14&ved=0CEMQFjAN&usg=AFQjCNHXJIdP9X-M6o8p_foi3qabOcjqMg&sig2=M0ZpY1NARNnI1-wSe2DxZg

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  Reply # 1092252 20-Jul-2014 00:25
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Would suggest getting an infinity gas water heater :) problem solved

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  Reply # 1092274 20-Jul-2014 06:12
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I can't help with the question, but had a mains pressure cylinder installed when we redid the bathroom a year or two ago. The old one was awful, hard to get the right temperature, incredibly fussy hot water tap, poor pressure, and an outdated bathroom. The new cylinder went into my huge roof cavity, as I suggested, and it's awesome, along with the new bathroom with Methven tapware. The temperature's anything you want, the pressure's great, and we got back a bunch of space. Highly recommend the upgrade.

We did a pretty good job of the bathroom, and despite staying in some nice hotels around the world we've never had one better than we built. Tiles most places, under floor heating, two shower heads (the rain head above us is about 50cm wide), etc, etc. Very expensive though.




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  Reply # 1092284 20-Jul-2014 07:05
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We've looked at both mains pressure and infinity, both quotes were just over three thousand bucks. The low pressure cylinder is only seven years old, so works wel despite the lowish pressure. The valve is only $100 so if it can solve most of our problems, that's 3k I'd rather spend in the bathroom itself!

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  Reply # 1092285 20-Jul-2014 07:23
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If the issue is with the shower, check that the shower head is clean and that someone did not install a pressure limiter.  The stock standard combiner shower mixer and head (think it is Methven?) has a colour coded valve you can replace yourself, for equal or unequal pressure etc.  It could have the wrong one.  Or like it was in our case, perhaps one of the taps at the cylinder are not fully open.

It should be safe going to the maximum head height allowed for your cylinder, but should get a plumber to confirm (and do the job).

Going to a new high pressure cylinder you will probably find most of your (old) taps leaking.  But increasing a pressure slightly should not cause any such issues.




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  Reply # 1092301 20-Jul-2014 08:47
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Niel: [snip]
It should be safe going to the maximum head height allowed for your cylinder, but should get a plumber to confirm (and do the job).


Check this before you do anything - it might not take any more pressure.



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  Reply # 1092319 20-Jul-2014 09:46
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RunningMan:
Niel: [snip]
It should be safe going to the maximum head height allowed for your cylinder, but should get a plumber to confirm (and do the job).


Check this before you do anything - it might not take any more pressure.




Yes, be very careful about increasing the pressure in the cylinder. If it should burst, you'd have a hell of a flood to deal with.

One advantage of the old low pressure cylinders is they tend to last a lot longer as there isn't the pressure on the cylinder seams shortening its life span.

Our house has a cylinder from 1966 and it's still going. I need to wrap it with something as it's not well insulated.




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  Reply # 1092334 20-Jul-2014 10:27
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We have a similar arrangement, the only difference being that our thermal overflow comes out of a valve into a pipe that drops it into a drain pipe - we could do that because the cylinder is beside a bathroom. I presume that you could get a similar valve put on your vent pipe. This would also allow you to cut down the pipe to roof level - they usually look unsightly.

Are you sure that your pressure reducing valve is not adjustable. We paid a little extra for that when we put ours in 8 years ago. Our pressure reducing valve is adjustable far above the limit for our low-pressure cylinder so we could easily burst the copper cylinder. It is currently set close to the upper limit of the cylinder.

For the information of other suggesting new water heating systems, there are good reasons for using these systems:

 

  • avoid wasting water pumped out at mains pressure - so going to continuous flow would not be an option that we would consider
  • lower maintenance with longer cylinder life
  • less susceptible to cylinder faults e.g. ceramic linings often crack
  • less susceptible to water quality problems
  • higher resilience in earthquakes
  • lower cost.

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  Reply # 1092375 20-Jul-2014 10:44
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DarthKermit:
...
Our house has a cylinder from 1966 and it's still going. I need to wrap it with something as it's not well insulated.


Get it done. Your payback on insulating an old poorly insulated cylinder could be as low as 6 months. I've even seen a 3 month return where they were spending $60 a month on cylinder heat loss. For most older cylinders the payback is unlikely to be more than two years at 55C. I've read a US report that demonstrated it can be economic to insulate cylinders up to about about 50 cm of insulation.

If you have higher cylinder temperature then insulation is far more economic because heat losses are proportional to the difference in temperature. So if it is 20C in the house and water temperature is increased 18% from 55C to 65C then the heat losses increase 28% = (65-55)/(55-20). In some circumstances the increase in heat loss would be higher. This happens where higher temperature differences can increase the convection currents and heat loss is also proportional to the flow rate of the water. That's why some hot water cylinders have baffles to control convection: to ensure the coldest water gets heated first; to prevent the hottest water at the top of the tank from mixing with cold water at the bottom of the tank; to prevent solar-heated water (entering at the bottom of the cylinder) from pushing cold water up to the top of the tank.

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  Reply # 1092385 20-Jul-2014 11:03
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sxz: We run a low pressure hot water cylinder. Supposedly 60%+ of nz does. Mains pressure cold runs through a pressure limiting valve into the tank, pushing hot water into the house at the pressure of that valve.

Due to thermal expansion we have an overflow pipe sticking straight into the sky, so if pressure gets too high it releases by bubbling over, no damage done.

Our pressure is on the poor side. My question is, if I install a pressure relief valve that stimulates another 3.6m of pipe on the roof (or if I install another 3.6m of pipe on the roof), and i dial up the pressure of the cold water pressure reducing valve so the internal task pressure is higher, will this likely damage my cylinder or should it have some in built tolerances?

Methven seem to suggest it as an option here, bullet point 6, page 1:

https://www.google.co.nz/url?sa=t&source=web&rct=j&ei=e1nKU6vFHouBywPDiIGoAw&url=http://www.methven.com/nz/specialist-brand/nefa/pressure-and-vacuum-relief--valve/install-sheet/285003.pdf&cd=14&ved=0CEMQFjAN&usg=AFQjCNHXJIdP9X-M6o8p_foi3qabOcjqMg&sig2=M0ZpY1NARNnI1-wSe2DxZg



Its is NOT just your hot water cylinder, it is also your plumbing.
Plastic pipes can take either the heat or the temperature, if you try both you may find your pipes bursting.

If its for a shower, look for one of the vortex type systems what uses the cold water flow to generate a low pressure point at the shower on your hot water causing MORE hot water to flow.

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  Reply # 1092404 20-Jul-2014 11:22
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sir1963:
sxz: We run a low pressure hot water cylinder. Supposedly 60%+ of nz does. Mains pressure cold runs through a pressure limiting valve into the tank, pushing hot water into the house at the pressure of that valve.

Due to thermal expansion we have an overflow pipe sticking straight into the sky, so if pressure gets too high it releases by bubbling over, no damage done.

Our pressure is on the poor side. My question is, if I install a pressure relief valve that stimulates another 3.6m of pipe on the roof (or if I install another 3.6m of pipe on the roof), and i dial up the pressure of the cold water pressure reducing valve so the internal task pressure is higher, will this likely damage my cylinder or should it have some in built tolerances?

Methven seem to suggest it as an option here, bullet point 6, page 1:

https://www.google.co.nz/url?sa=t&source=web&rct=j&ei=e1nKU6vFHouBywPDiIGoAw&url=http://www.methven.com/nz/specialist-brand/nefa/pressure-and-vacuum-relief--valve/install-sheet/285003.pdf&cd=14&ved=0CEMQFjAN&usg=AFQjCNHXJIdP9X-M6o8p_foi3qabOcjqMg&sig2=M0ZpY1NARNnI1-wSe2DxZg



Its is NOT just your hot water cylinder, it is also your plumbing.
Plastic pipes can take either the heat or the temperature, if you try both you may find your pipes bursting.

If its for a shower, look for one of the vortex type systems what uses the cold water flow to generate a low pressure point at the shower on your hot water causing MORE hot water to flow.


"Venturi" type mixers I think is the term.  We have one (Felton?) with LP (header tank) HWC system.  It does work - I replaced a standard uneven pressure mixer with it a few years ago, and it made a difference (but don't expect it to become like a high pressure needle jet shower)  IIRC the venturi and pressure reducer on the cold inlet can be removed so it works on equal pressure - when our HWC dies, then I'd upgrade to a mains pressure system.
Another thing causing poor shower pressure can be cheap shower extension hoses.  They look "metal", but some have poor quality internal hose liners which delaminate and kink, blocking flow - even if the outer coils look fine.  Good quality hoses don't cost a lot more - if you shop around.

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  Reply # 1092467 20-Jul-2014 13:46
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You can get a shower boost pump if its just the shower you want to sort out. This wont affect any of your other plumbing.

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  Reply # 1092492 20-Jul-2014 14:23
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Hammerer: Get it done. Your payback on insulating an old poorly insulated cylinder could be as low as 6 months. I've even seen a 3 month return where they were spending $60 a month on cylinder heat loss. For most older cylinders the payback is unlikely to be more than two years at 55C. I've read a US report that demonstrated it can be economic to insulate cylinders up to about about 50 cm of insulation.

If you have higher cylinder temperature then insulation is far more economic because heat losses are proportional to the difference in temperature. So if it is 20C in the house and water temperature is increased 18% from 55C to 65C then the heat losses increase 28% = (65-55)/(55-20). In some circumstances the increase in heat loss would be higher. This happens where higher temperature differences can increase the convection currents and heat loss is also proportional to the flow rate of the water. That's why some hot water cylinders have baffles to control convection: to ensure the coldest water gets heated first; to prevent the hottest water at the top of the tank from mixing with cold water at the bottom of the tank; to prevent solar-heated water (entering at the bottom of the cylinder) from pushing cold water up to the top of the tank.


I was thinking of buying one of those mylar survival blankets and wrapping it around. That's because there's only a gap of 10 mm on one side, so one of those thick blanket wraps wouldn't fit. I've already turned the water temp down to 130 degrees Fahrenheit (yes it's that old) which is 55 degrees C.




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  Reply # 1092494 20-Jul-2014 14:29
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Get a standard hot water cylinder wrap. They'll compress down to less than 10mm with a bit of a push.




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  Reply # 1092513 20-Jul-2014 15:18
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Seriously consider an upgrade to a mains pressure system comes with modern standard insulation. You are going to spend time, $, and risk squeezing extra performance out of the old one. It will have a maximum head rating see if you can find that.

Alternatively consider instant hot water for the shower you can run mains pressure straight to that and keep the rest of the system. Yeah probably not worth it but it is an alternative to full replacement.

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  Reply # 1092515 20-Jul-2014 15:25
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sxz: The low pressure cylinder is only seven years old, so works wel despite the lowish pressure. The valve is only $100 so if it can solve most of our problems, that's 3k I'd rather spend in the bathroom itself!

Should be easy to find out the maximum head for that and get an appropriate valve fitted or head added. Imo chances are with a recent install it will be running at maximum anyway, which means you have other things to look at in the system.

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