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Posted
4 hours ago, John Carroll said:

You said the EV was flat, what pressure was it recharged to?, it should also have been done at the very least with the cold mains to the cylinder shut off and a HW tap opened, if its located above the cylinder then that should be OK.

 

Originally 3 bar and it's located above the cylinder. I'll make sure I do what you say when I recharge it (didn't manage to do it over the weekend). I've turned off my immersion diverter for the moment, so the temperature in the tank won't exceed ~50° C until I've got all of this sorted out. 

 

4 hours ago, John Carroll said:

I would also suggest checking that there is a pressure reducing valve (PRV) installed (which there should be) on the cold water valve set and most/more important that its setting is checked.

 

There's a 3 bar pressure reducing valve on the incoming mains. I already have a pressure gauge on its way so I can test it.

 

4 hours ago, John Carroll said:

Even with your 22L EV and assuming that you will rarely if ever be reheating a full cylinder, more likely say 80% or 200L then a final pressure of 3.12bar at 60C & 3.25bar at 65C with a cyl prepressure of 2.3bar, 2.5bar (if available) will still give over 90% flowrate of a 3.0bar cylinder.

 

Okay, thanks. I'm going to have a think about the setup as a whole. Currently considering adding an additional expension vessel to the cold feed near the tank, as there's more space there than where the current one is near the ceiling.

 

4 hours ago, John Carroll said:

Is the blue PRV next to the (red) TPR also stamped as set to 4.5bar?

 

There are two valves: 3.5 bar pressure relief, and 90-95°/4.5 bar temperature/pressure relief.


Thanks again, I appreciate the feedback.

  • Like 1
Posted (edited)

From the horse's (McDonald Water Storage) mouth, the MI's show, below, the expansion relief valve mounted on the cylinder as yours is and none on the valve set (again like yours), the PRV should be set to 2.1bar, likewise the EV charge pressure....set to 2.1bar  and that's why a 22L EV is perfectly acceptable under those conditions, a full reheat to 60C then gives a final pressure of 2.8bar, 65C gives 2.91bar & 70C gives 3.12bar. all comfortably below the expansion relief valve's 3.5bar setting.

 

 

image.png.cb28e49ab0c459e1c2e2f5d022001141.png

 

 

 

image.png.bcd993db7d41cb156efde2f0da898521.png

ECOFlow-Installation-Manual.pdf

Edited by John Carroll
  • Like 1
Posted
13 hours ago, John Carroll said:

From the horse's (McDonald Water Storage) mouth ...

 

Thanks John. I found that document a couple of days ago. It was one of the triggers for my comment about rethinking the setup as a whole. It's frustrating the original plumber apparently didn't read the manual before installing a 3 bar PVR on the incoming mains 10 years ago! 

 

While it's been fine operating at 3 bar for 10 years, I'm going to lower the incoming PRV to the recommended pressure. I'll also install another expansion vessel to help keep the pressure low.

 

While static pressure is fine, it does drop noticeably if a couple of showers or taps are in use. I suspect the most likely culprit is the water softener, but I'll be doing some pressure tests on the weekend to see what I can learn.

 

Either way, I'd like to do what I can (within reason) to avoid making the crappy dynamic pressure any worse when I change to the lower pressure PRV on the incoming main.

Posted
43 minutes ago, jack said:

 

Thanks John. I found that document a couple of days ago. It was one of the triggers for my comment about rethinking the setup as a whole. It's frustrating the original plumber apparently didn't read the manual before installing a 3 bar PVR on the incoming mains 10 years ago! 

 

While it's been fine operating at 3 bar for 10 years, I'm going to lower the incoming PRV to the recommended pressure. I'll also install another expansion vessel to help keep the pressure low.

 

While static pressure is fine, it does drop noticeably if a couple of showers or taps are in use. I suspect the most likely culprit is the water softener, but I'll be doing some pressure tests on the weekend to see what I can learn.

 

Either way, I'd like to do what I can (within reason) to avoid making the crappy dynamic pressure any worse when I change to the lower pressure PRV on the incoming main.

If you can leave a 5bar PEV feeding the softener, and only drop to 2.1 at the cylinder group then that would help. 
 

If your incoming cold mains will never see 5 bar then just leave a raw feed to the softener. 
 

Can you install a 150 or 200L accumulator anywhere, as this would make a big difference. 

Posted

If, (which it probably has been) the EV precharge pressure has/had been set to 3.0bar and even assuming that the cold water pressure after the PRV (set to 3.0bar) never went higher than 2.0bar before reheating then the expansion relief valve would still have lifted if ~ 150L or more of the UV cylinder required reheating to 60C.

 

My ancient spreadsheet, below, may be of interst and be a help in sizing calculations for either HW or CH.

EV CalcsJK Rev0.xlsx

  • Like 2
Posted
On 19/08/2025 at 11:19, Nickfromwales said:

If you can leave a 5bar PEV feeding the softener, and only drop to 2.1 at the cylinder group then that would help. 
 

If your incoming cold mains will never see 5 bar then just leave a raw feed to the softener. 
 

Can you install a 150 or 200L accumulator anywhere, as this would make a big difference. 

 

Just coming back to this after spending some time reading and thinking over the weekend.

 

First, I've installed the new 3.5 bar pressure relief valve, turned off the immersion diverter, and reduced the inlet PRV pressure to 2.2 bar while I sort all of this out. 

 

Second, @John Carroll, your spreadsheet was hugely helpful, so thanks again for sharing it. While I understood the general principle behind expansion vessels, seeing the actual numbers was eye-opening to say the least. A few percent expansion doesn't sound like a lot, but when you combine it with a limited maximum DHW tank pressure and an immersion diverter, the peak operating pressure very quickly gets problematic. 

 

As an example, with a starting temp of 10 °C and a finishing temp of 70 °C (not crazy numbers with the immersion diverter working on a sunny day with colder mains in the autumn), the inlet PRV set at 2.5 bar, and my current 22 L expansion vessel, the final guage pressure of the system would exceed 3.5 bar. Adding a 50 L expansion vessel would drop the final pressure to 2.8 bar. 

 

2.2 bar is proving to be unpleasantly low in practice, so I really want to bump that number up with a larger expansion vessel or accumulator.

 

Using the nominal operating parameters in the cylinder manual (2.1 bar inlet PRV, operating temp 65 °C), and assuming an inlet temp of 7 °C (doubt it ever gets much lower in my circumstances), gives a peak pressure of about 3.1 bar. This should be a reasonable guide to a maximum operating pressure.

 

By fitting an additional 80 L expansion vessel, I can run at close to 3 bar on the inlet PRV while keeping a similar peak pressure.

 

Even allowing for a final temperature of 80 °C, I'd still be 0.2 bar below the 3.5 bar set by the pressure relief valve. These are pretty extreme numbers, so I should rarely reach them.

 

@Nickfromwales, I know the difference in principle between an expansion vessel and an accumulator, but in practice, is there any benefit to choosing one over the other? Are they structurally different? I see diaphragm versus bladder - are diaphragms intended to stretch, so that the pressure buffering is partly provided by the elasticity of the membrane? In general, would you expect either type to last longer than the other?

 

The 22 L expansion vessel would stay in place near the outlet at the top of the tank. I assume the new vessel/accumulator would go after the water softener in this diagram?:

 

image.png.f2a9d5119472d9418d9bfb339d23097c.png   

I also plan to install a new PRV between the softener and the new pressure vessel/accumulator, so that the 3 bar supply is set after the water softener.

  • Like 1
Posted

The attached may be of some help re Accumulator.

For example assuming a 200L accumulator and a required UVC pressure of 3bar, then if 4.0bar mains is available to recharge the accumulator you end up with a net vol of 40L. If you install a pumped accumulator and assuming you can pressurize it to 6.0bar then the net vol is 86L

Accumulator CalcsJK Rev0.xlsx

  • Thanks 1
Posted
1 hour ago, John Carroll said:

The attached may be of some help re Accumulator.

For example assuming a 200L accumulator and a required UVC pressure of 3bar, then if 4.0bar mains is available to recharge the accumulator you end up with a net vol of 40L. If you install a pumped accumulator and assuming you can pressurize it to 6.0bar then the net vol is 86L

Accumulator CalcsJK Rev0.xlsx 15.46 kB · 3 downloads

 

Thanks John.

 

I think the numbers for using an accumulator as an accumulator (rather than as a glorified expansion vessel) don't work that well in my case. Our mains is only about 3.4 bar, so realistically we'd need to consider a pumped system to get useable volume out of it. A 200 L accumulator + pump + additional pipework/valves would add a lot of cost and complexity, plus we don't really have space for a 200 L accumulator.

 

Having done a bit of research, I don't think there's any benefit in using an accumulator instead of an expansion vessel in this application. They don't seem to be much cheaper.

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