Water Supply - Pressure Issue

[iSelfBuild]

I am building three lodges/log cabins in a woodland site which has a rather questionable water system.

 

The supply comes into the lower site via a Scottish Water mains and is terminated at the edge of the site. It's then taken up in private pipes to the plots in 50mm and teed off to each plot in 32mm.

 

This is 20m lower than some of the plots. A few years ago the mains water was intermittent throughout the day in terms of flow - i.e. not enough pressure when in peak use locally.

 

I wasn't involved in the 'fix' implemented - which was to install a small pump house, extra pumping delivery pipe in 50mm and a 5500 l header tank at the top of the site 30m up. This 5,500l tank is filled with mains pressure when it exists and topped up with the pumps at night time. This has worked well for a number of years for some of the plots that are right at the bottom and benefit from the head of pressure and delivery pipe being all down hill and when not many people were drawing off it.

 

It's now getting close to empty throughout the day in peak use. So we are going to modify the system to pump on demand whenever 1000 litres is taken out of the tank.

 

There is another issue with this system - 4 of the plots are getting just about bearable water pressure. However my sites which raise up another 6m from the delivery pipe are getting just 1/3 bar pressure - with 15 litres flow per minute.

 

I was going to fit a small 60l pressure vessel and pump at the bottom of the sites to ensure I always have pressured water on demand. Something like this: https://www.plumbworld.co.uk/salamander-accuboost-60l-pumped-accumulator-tank-acc-060-sys-19703-1263509

 

However after mentioning it to some of the other plot owners we thought a communal system could be better so it benefits everyone.

 

I would need to expose the pipe that comes down from the header tank and fit a check valve before anything is drawn off of it. Then tee off to a pump and pressure switch which is linked to perhaps a 300 litre pressure vessel. Then re-tap into the header tank down pipe (after the check valve)

 

It would seem this would work, 5,500l header tank is probably an OK size for 8 properties but I'm wondering if the pressure vessel at 300litres would be big enough? I'm aware more could be connected in series.

 

All very heath Robinson and I think pumping it up 30m and building a big tank at the bottom of the site was a waste of time. They should have just had a pressured system and break tank from the outset at the bottom.

 

 

 

However 

[Conor]

Would be much simpler just to have a booster pump at the site inlet and do away with the tanks etc. If you only have a ~20m change in elevation, a pump that produces 30m head (3bar) would be enough (assuming effective 0m head at times at the inlet to the site). Individual PRVs can be fitted to units to get pressure below 3bar of needed.

Edited August 14, 2021 by Conor

[Temp]

So the supply comes on site (call that 0m) and is pumped up 30m to a tank. However some plots are at 20m and 26m up so they are only 10m and 4m below the tank. So the worse plot should get 4m head (0.4 bar) which is consistent with what you say about them getting "1/3 bar pressure". Have I got that right?

 

I think I'd do a proper review starting with the demand....  What peak flow will the site need in the future? Any further expansion planned? If you just use a pump to boost the pressure can the main deliver that peak flow rate at the time of day when it occurs? If not then some sort of storage is needed to average down the peak flow.

[iSelfBuild]

Yep that's correct. Assuming 8 people drawing off the 5,500l header tank - we would need a pump capable of filling a pressure vessel at (14 litres per minute x 8 ) 112 litres per minute and it would need to pressurise this to say 3 bar. Looking at pumps this is nothing special or too demanding. If that was connected to a 300 litre pressure vessel set a 3 bar. Then in theory everyone drawing off 14 litres per minute the vessel would have pressurised capacity for nearly 3 minutes before the pump kicked back in. In reality the pump would probably kick in every 20 minutes or so unless it was a peak use time (everyone having their showers on at 8 am for example)

 

Is my logic right?

 

Whole system is very Heath Robinson. Cat 5 water tank and pump should have been fitted onto the mains from the outset and done away with a holding tank 200m up the site (30m head) so much pointless trenches dug and pipework.

 

 

 

 

 

 

[Temp]

Seems reasonable if the incoming main can always supply 112L/min. I'm not familiar with the regs. Are you allowed to pump the mains direct these days?

[iSelfBuild]

It wouldn't be pumping the mains we would be just pressurising the downflow from the 5500l header tank.

 

Where we do pump off the mains (up to the header tank) we have a break tank. You can actually pump directly off the mains but I think 13 litres or something is the limit per minute or thereabouts.