Water Softener recs for maximising flow rate

[Dan F]

1 hour ago, fezster said:

My PRV is "drop tight", so the static pressure won't creep up. I'm not sure what a "dynamic prv" is? Mine is a Reliance 28mm Predator 315i.

Dynamic control PRV limits dynamic pressure and not static pressure.

 

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I do agree with your point that the dynamic pressure may be limited by the incoming supply pipe.

That is the only real explanation IMO.

 

1 hour ago, fezster said:

What I'm not sure about is whether the dynamic pressure can ever differ anywhere in a pipe run - ie. If you have a 100m pipe with 20l/min flowing through it, then surely the dynamic pressure is the same at any point in that pipe run? If that is true, then having a prv at any point in that pipe run will surely not matter. The pipe run itself has a pressure loss, just as any fitting or water softener has losses, and therefore a prv before or after a fitting/softener shouldn't affect the overall dynamic pressure the pipe run is capable of providing. Not sure if I've explained that very well, but that's how I make sense of it in my head.

If there is pressure loss in a pipe run, then the dynamic pressure clearly is not the same everywhere!

 

Edited February 12, 2022 by Dan F

[fezster]

11 hours ago, Dan F said:

Dynamic control PRV limits dynamic pressure and not static pressure.

 

 

Can you explain what this means?

 

A PRV is pretty basic in it's operation - a spring loaded diaphram controlled valve. The force of the spring maintains the outlet pressure, regardless of inlet pressure. Maybe if you could provide an example of a dynamic pressure PRV vs a static pressure PRV?

 

The "drop tight" PRV's guarantee that as well as controlling dynamic pressure, they will not allow the static pressure to creep up under no-flow conditions. That's the only difference I'm aware of.

 

11 hours ago, Dan F said:

If there is pressure loss in a pipe run, then the dynamic pressure clearly is not the same everywhere!

 

 

Yes, you are correct. I'd definitely gotten myself confused with my own setup. This video here clearly explains the difference in pressure with varying pipe sizes:

 

https://practical.engineering/blog/2021/4/6/flow-and-pressure-in-pipes-explained

 

What I would say, though, for the example of the water softener and a PRV either side is that this would only be beneficial if the dynamic pressure is higher than whatever you would set your PRV to. In my case, as the dynamic pressure is already under 3 bar, a single PRV before or after the softener would maintain anything up to 3 bar. As it happens, my PRV is actually after my softener.

 

Do any domestic dwellings have a dynamic pressure over 3 bar for a flow rate of > 20L/min? Certainly in London, you'd be lucky to get anywhere near that.

 

[Dan F]

On 13/02/2022 at 11:21, fezster said:

Can you explain what this means?

It does what it says on the tin.  See https://www.plumbingmag.com/pressure-reducing-valves-dynamic-vs-static/

 

On 13/02/2022 at 11:21, fezster said:

as well as controlling dynamic pressure, they will not allow the static pressure to creep up under no-flow conditions

Yes, downside is that dyanmic pressure under flow is lower than what PRV is set to.  Typically this is unavoidable though because a dynamic PRV doesn't control static pressure, which is a requirement for unvented UVC I think.

 

On 13/02/2022 at 11:21, fezster said:

What I would say, though, for the example of the water softener and a PRV either side is that this would only be beneficial if the dynamic pressure is higher than whatever you would set your PRV to.

Yes of course.

 

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In my case, as the dynamic pressure is already under 3 bar, a single PRV before or after the softener would maintain anything up to 3 bar. As it happens, my PRV is actually after my softener.

Right.  If you assume loss (at 20L/min) via water softener is 0.5bar and loss via PRV is 0.5bar and you have static PRV set to 3-bar, then I thnk:

- PRV before gives you 2 bar
- PRV before gives you 2.5 bar (assuming supply give dynamic pressure >=3.5 bar)

 

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Do any domestic dwellings have a dynamic pressure over 3 bar for a flow rate of > 20L/min? Certainly in London, you'd be lucky to get anywhere near that.

Depends on your supply as well, not just the area.  i.e. do you have 25mm supply on 15mm meter, or 32mm supply.

 

Edited February 14, 2022 by Dan F

[fezster]

I have a 32mm mdpe incoming. Static pressure can be between 3.5 and 6 bar, depending on time of day. 

 

Did a small test today. My PRV is after my water softener. With the shower running (approx 20 l/min), dynamic pressure is 2.5 bar. I bypassed my softener - given everything discussed above, I expected the dynamic pressure to increase, albeit slightly. It didn't budge. So a little confused, as there's no way a softener can't have some pressure loss across it. 

[Dan F]

4 hours ago, fezster said:

I have a 32mm mdpe incoming. Static pressure can be between 3.5 and 6 bar, depending on time of day. 

 

Did a small test today. My PRV is after my water softener. With the shower running (approx 20 l/min), dynamic pressure is 2.5 bar. I bypassed my softener - given everything discussed above, I expected the dynamic pressure to increase, albeit slightly. It didn't budge. So a little confused, as there's no way a softener can't have some pressure loss across it. 

What is outside tap presuse when running 20l/min?