The House at the Bottom of the Garden

We've had a Harveys, a Kinetico and a Twintec over the years. The only one to give any problem was the Twintec although I liked it because it had a see through cover over the salt container. Wrekin Water Softeners do their own version.

Looking at that pressure loss curve I don't think I'm going to fret over it, TBH.  With our shower running the pressure drop through the softener is only around 0.2 bar, and I can say from experience that we can't notice a 1 bar difference at any of the outlets, as that's the normal variation we get between the borehole pump turning on and off (it turns off at 3.5 bar and on at 2.5 bar).  Given that a 1 bar variation seems to have no noticeable impact, and as we'd need to draw off at three times the shower flow rate to get a 1 bar drop, I'm not sure that it's something really worth worrying about, unless you have a low mains supply pressure.

 

Our accumulators are on the hard water side, too, as they have to be in order to not put a reverse flow through the softener if one of the garden taps was used.  As I mentioned elsewhere, if the pressure at the softener outlet is slightly higher than that at the inlet then it can overflow the brine chamber.  Even with an NRV in line I think I'd be wary about fitting an accumulator on the outlet side, as NRVs aren't perfect one-way valves, they will momentarily allow a small reverse flow as they shut.  I found this out with the ones I fitted to the water treatment system, at the ozone injection point, and having discovered this the regs that say you must have a double NRV on the incoming supply makes perfect sense; it's to prevent that tiny, momentary, bit of reverse flow, I think.

 

If you have a high enough incoming mains pressure then the option of fitting a PRedV after the softener, to regulate the pressure to a usable figure, say 2.5 to 3 bar, might be an option.  That way the pressure drop through the softener might well have no effect at all.

Edited February 18, 2017 by JSHarris

Jeremy, thanks for the feedback. 

 

Anglian Water pump the supply where we live and keep it to just a tad over 3 bar.  This sort of drop is liveable with for most scenarios, and it works for us, but it is still big enough that self-builders need to be aware of this in planning their systems.  I'll discuss this in my next blog post.

Impressive presentation from the landlady.

 

http://www.roomsinreading.co.uk/

As I live in ( sunny ? ) Wales, ill admit to having fitted only one or two water softeners. 

In the most recent install I fitted a 300 litre accumulator, post softener, so I can't document or comment on the individual performance of the softener ( as a stand alone item ) I'm afraid.

However.

This does form a good exchange, adding another important consideration for 'ye' of hard water' when designing the DCW system, ( the system which also will end up providing the energy required to propel your DHW out of the outlets  ), as losses from such resistances created by such additional / peripheral equipment may easily be overlooked when deciding whether an accumulator is required or not. 

 

3 hours ago, JSHarris said:

Looking at that pressure loss curve I don't think I'm going to fret over it, TBH.  With our shower running the pressure drop through the softener is only around 0.2 bar, and I can say from experience that we can't notice a 1 bar difference at any of the outlets, as that's the normal variation we get between the borehole pump turning on and off (it turns off at 3.5 bar and on at 2.5 bar).  Given that a 1 bar variation seems to have no noticeable impact, and as we'd need to draw off at three times the shower flow rate to get a 1 bar drop, I'm not sure that it's something really worth worrying about, unless you have a low mains supply pressure.

 

Our accumulators are on the hard water side, too, as they have to be in order to not put a reverse flow through the softener if one of the garden taps was used.  As I mentioned elsewhere, if the pressure at the softener outlet is slightly higher than that at the inlet then it can overflow the brine chamber.  Even with an NRV in line I think I'd be wary about fitting an accumulator on the outlet side, as NRVs aren't perfect one-way valves, they will momentarily allow a small reverse flow as they shut.  I found this out with the ones I fitted to the water treatment system, at the ozone injection point, and having discovered this the regs that say you must have a double NRV on the incoming supply makes perfect sense; it's to prevent that tiny, momentary, bit of reverse flow, I think.

 

If you have a high enough incoming mains pressure then the option of fitting a PRedV after the softener, to regulate the pressure to a usable figure, say 2.5 to 3 bar, might be an option.  That way the pressure drop through the softener might well have no effect at all.

 

Probably best to highlight the fact that you do, indeed, have multiple accumulators in this scenario, ( to compliment / tame  your borehole water supply ), so that anyone reading this can gauge their response / thoughts about whether one would be necessary for eg a property 'suffering' from possible constraints associated with having a basic domestic cold mains supply which is supplying said house ( with a softener ). 

Surveying for an accumulator requires static and dynamic pressure readings at various times of the day, eg when the network is under strain vs when it's relaxed, in order to ascertain if such a medium is required or not. Adding together the combined resistances of the connected equipment, after the stopcock, is where this discussion gains its merit as most won't give this the thought that it's due when considering a system. Worse than that, they may well simply take advice from their chosen plumbing contractor who, for the lack of knowing differently, may just carry on as they did with the last job, not paying sufficient attention / consideration to the current remit. 

An entire subject of its own IMO, and well worth the effort and input of this exchange. . 

True, but they are all on the input side, and they still give a 1 bar variation in pressure between the pump cut-in and cut-out pressure, so as far as the input to the softener is concerned it sees between 2.5 bar and 3.5 bar incoming pressure, so it's just the same as a mains supply with that amount of normal variation.

I didn't go into any of this myself, as all the calculations and design were done by the plumber.

 

Our situation is a little odd.  Our plumber wanted to make sure that if the building inspector decided to test the flow rates of any outlet, they'd all definitely pass.  Rather than fit flow reducers at every outlet, he (with our agreement) temporarily fitted a 1.5 bar PRV on the incoming main.  Over a year later and it's still there!

 

The result of this low pressure is that if our water softener decides to run a cycle while you're in the (upstairs) shower, there's a very marked drop in water pressure.  That's with a single shower and no water being supplied anywhere else.  The shower is still usable when it's like this but it's not great.

 

Similar to Jeremy, we binned the "full bore 22mm" flex hoses when we saw how small the actual apertures were. The unit was then plumbed using 22mm copper and plastic, so there shouldn't be much restriction.

  

I don't know whether this helps at all, but perhaps it shows that even at 1.5 bar you can at least have a shower while the softener is recharging, as long as you're patient!

Here's the schematic of my PRV.  The slider which controls the flow from the inlet is set by an equilibrium between dynamic water pressure on the output side acting on the diaphragm and the compression is the adjustment spring.  The next figure is the Harvey recommended positioning of the PRV.  

 

Since my static pressure is barely 3 bar, the dynamic pressure under load is going to be less than this.  The typical dynamic pressure on the PRV inlet side also include the pressure loss through the Harvey, so for anything other than trivia flow rates, the valve will be pretty much fully open.  And in fact on our system, I suspect that the PRV will always be open if set at 3 bar or higher.

 

Jeremy is correct that any accumulator on the manifold side will have a standing pressure of around 3 bar, so if the garden is suddenly fully opened then the mains supply side could drop below 3 bar causing a small back flow until the double check valve kicks in.

 

@JSHarris,  Jeremy a little Q:  what would happen if you replaced the bypass stopcock with a 2 bar PRV? 

47 minutes ago, jack said:

Our situation is a little odd.  Our plumber wanted to make sure that if the building inspector decided to test the flow rates of any outlet, they'd all definitely pass.  Rather than fit flow reducers at every outlet, he (with our agreement) temporarily fitted a 1.5 bar PRV on the incoming main.  Over a year later and it's still there!

 

Jeff, remove it or at least crank it up to 3 bar and fit the flow limiters where you want them.  (see my next blog post).

The PRV isn't adjustable and I have more than enough to do to complete the house without having to replace the PRV and go around fitting flow-limiters everywhere!  I'll get the PRV replaced (with an adjustable one) once the house is signed off.

 

It isn't that big a deal in the meantime.

2 hours ago, TerryE said:

Here's the schematic of my PRV.  The slider which controls the flow from the inlet is set by an equilibrium between dynamic water pressure on the output side acting on the diaphragm and the compression is the adjustment spring.  The next figure is the Harvey recommended positioning of the PRV.  

 

Since my static pressure is barely 3 bar, the dynamic pressure under load is going to be less than this.  The typical dynamic pressure on the PRV inlet side also include the pressure loss through the Harvey, so for anything other than trivia flow rates, the valve will be pretty much fully open.  And in fact on our system, I suspect that the PRV will always be open if set at 3 bar or higher.

 

Jeremy is correct that any accumulator on the manifold side will have a standing pressure of around 3 bar, so if the garden is suddenly fully opened then the mains supply side could drop below 3 bar causing a small back flow until the double check valve kicks in.

 

@JSHarris,  Jeremy a little Q:  what would happen if you replaced the bypass stopcock with a 2 bar PRV? 

 

 

First off, if the pressure on the manifold side of the softener is even a tiny bit higher than that on the inlet side I think there is a risk that the situation we had may occur.  Once this happens, it doesn't self-correct when the pressure differential is sorted out, water continues to flow slowly into the brine tank until the softener is isolated and then the pressure released, using the valves and an open outlet on the house-side.  When the valves are then operated in the correct sequence (outlet valve closed, inlet valve and main supply stop cock opened, bypass valve closed, outlet valve opened) the softener resumes as normal, but the brine tank needs to be emptied of excess brine and there is a chance that there will be brine in the water supply, too (we had pipes full of salty water that had to be flushed).  Having experienced this, I think I would be extremely reluctant to fit an accumulator on the manifold side of the softener, attractive as it may seem in terms of buffering the pressure loss in the softener itself.

 

I guess you could fit a 2 bar PRedV in place of the bypass, but they are usually also NRVs, so I'd be concerned about the pressure differential issue.  I keep meaning to call Harvey's about this, as it's not clear from anything I've read from them that this reverse-pressure problem can occur.  It may well be that it's not something that happens except under a very rare set of circumstances, as we only had it happen once.  In our case the higher pressure on the outlet side was because of the small pressure vessel on the old thermal store; it was enough to retain a 3.5 bar head on the outlet side with the valve closed, and I'd released the pressure on the inlet side deliberately to alter the upstream pipe work.  I just didn't think it mattered whether I opened the inlet side or outlet side valves in any particular order when I turned everything back on, and the outlet side valve was nearest..............

On reflection, I agree about the accumulator.

 

So let's focus on this PRV option.  If you thing about it, a PRV bypass can't cause a back flow whatever happens.  If you replaced it by a direct through pipe then all this is doing is connecting the input and output of the filter to the same source supply and you'd get no flow, surely?  What the PRV does is to open the valve based on the dynamic head in the output chamber of the valve so that at a two bar setting it is fully closed if this dynamic head is 2 bar.  With a mains pressure of 3 bar this pressure would be greater than 2 bar if the PD across the filter was less than 1 bar. 

 

Let's say we had a demand flow of 40 l /min, say -- as the PD across the filter started to go to more than 1 bar (which is roughly the 30 l/min flow rate), then the  bypass PRV would start to open allowing a second direct flow bypass limiting the PD across the filter to 1 bar so roughly 30 l/min would flow through the filter and 10 l/min unfiltered would bypass it, giving a 3:1 mix of filtered to unfiltered water.   This is a pretty unusually high rate and might only occur <1% of the time, so the potential scaling risk from this is negligible.  However, at least the supply could then cope with these higher flow rates in a graceful manner. OK, the mix thresholds would vary according to the mains pressure, and if this did drop to 2 bar or below then you'd have the filter largely bypassed since the balance would by determined by the PD across the TMV.  and if the mains was higher than 3 bar, then the percentage mix would be higher. 

 

I don't see our demand really ever getting above the sort of 25-30 l/min level, so I would bother with doing this, but I think that it would be an option for someone with a teenage or young adult family with high shower loads first thing in the morning.