Unvented pressurised system - some say you can’t add a shower pump - technically why (forgetting any legal restrictions if there any)

[Mikerightsecondtime]

Some say why do you need a shower pump if you have balanced mains pressure in an invented system? Well, think about this: cylinder is on ground floor, top room in 3rd floor loft conversion which has a shower. Assuming starting at 3 bar at ground level, the loss of bar pressure by the time the water has pushed up nearly 7m to the shower head outlet on 3rd floor reduces the shower output to tolerable but not great. I’m thinking get the pipes on 3rd floor shower, run them into a Stuart turner pump, and hey presto nice shower! The pump isn’t a mind reader: it doesn’t know if the water coming into it is from gravity cold water tank above or from the cylinder and mains below. Before anyone says “oooh, you’re not allowed to pump the mains, oooh” I’m interested in the technical reason why this wouldn’t work (or confirmation it would), rather than lots of ooohs, you caaaaan’t, ooh not allowed!

 

[Mikerightsecondtime]

This doesn’t mean I’m going to do it; it’s more for learning the technical barriers (are there any - if so what are they and why would they happen) - or is it all just a legal barrier?

 

[polesapart]

in an invented system?

You can imagine whatever you like.

 

[Mikerightsecondtime]

You can imagine whatever you like.

 

[Mikerightsecondtime]

Welcome any real life informed answers if someone put a pump on the shower pipes I’m fairly sure a sink hole won’t emerge in the street and swallow the neighbourhood.

 

[Elkato531]

3 bar at ground level would still be giving you 2.3 bar at a height of 7m. Should be adequate for a decent shower. If the flow from the shower is poor, it is more likely to be restrictive pipes and fittings and not lack of pressure.
As for pumping off the main, you run the risk of reducing the pressure in the main available for everyone else. Not significantly if your the only one doing it but if it was common practice it could lead to problems. Also, if there is a drop in mains pressure due to a burst main or shut down for maintenance, when your pump kicks in it could lead to backflow into the main from other open outlets. This backflow could present a serious contamination risk. Believe it or not, water regulations are not invented to make your life difficult. People who know far more than you have established a set of rules which help to keep us all safe and adequately supplied.

 

[Mikerightsecondtime]

Ever heard of a NRV?

 

[Elkato531]

Ever heard of a NRV?

Probably fitted thousands. Sadly not all outlets are protected and leaks on the main certainly aren't.
When you install your shower pump are you going to go round to all your neighbours and ensure every outlet is protected.

 

[Mikerightsecondtime]

Backflow can be easily addressed with a check valve surely? Water main depletion due to a shower pump is a theoretical not real issue. In the same way - of everyone on the street turns all their taps and hoses on at the same time (for which there are no rules to ‘keep us all safe’) they will all have no pressure due to depletion - this is a theoretical risk in a text book, not real life risk. So I’m still not hearing a real reason why the main could not safely be pumped - is it just the law only, and there is no technical or safety reason why it could not be done?

 

[Mikerightsecondtime]

How can backflip get out of my house via the main to my neighbours house, if I have installed a check valve?

 

[Mikerightsecondtime]

Backflow, not flip? Although probably more chance of a backflip getting into the neighbour

 

[Elkato531]

Not backflow FROM your house. In theory you could be pulling water from a main which has no pressure in it. This could lead to backflow into the main from elsewhere. The water regulations have to take into account possible risks even if you think they are unlikely.

 

[Hugh Jaleak]

If everyone in the street turned their taps on at once, you'd probably notice somewhat of a decrease in available pressure and flow from your tap, but that's about it. Water Companies have statutory obligations to provide a minimum pressure, and you'd be going some for demand to exceed supply. The Network is closely monitored, and the supply varied according to demand.

If a Water Main bursts, then the main could well empty and draw back in from any outlets higher than the burst. Hence why we have Backflow prevention devices.

 

[Mikerightsecondtime]

Still no answers. So, the pump put on the main would (a) have a check valve installed with it, to stop any back flow, and (b) have a flow switch that would stop the pump if a lack of flow was detected (eg supply from the main was cut off due to a burst main etc. why has no-one mentioned that you can legally and safely pump up to 12lts pm directly off the main, using widely available products, and that is fully within regs? Clearly none of the problems being touted are real - even the regulators think so - provided you are not pulling water out like a fire engine.

 

[dilalio]

Yes you can pump mains up to a certain rate, that's a known.

But this is done on your incoming main, before any outlets tanks, boilers etc.

To put one downstream of a UV, you'd likely be voiding any warranties you have.

There's also the possibility of the cylinder not withstanding ANY negative pressure put upon it (by a pump). While perhaps not fully imploding, it could become weakened over time, due to distortion and flexing of the welds.

You'd have to have an "open" conversation with the manufacturer about that.

Yes, regs are there. We have to abide by them in order to trade as much as anything. You perhaps do not, but will be liable should anything go wrong and cause damage or injury.