Thread: Ring mains - pressure drop

A 'ring main' is normally a loop servicing the entire distribution system, not just a part of it.

Water encounters a flow resistance as it travels through a pipe. The resistance encountered increases with length of pipe, the flow rate through the pipe, and reduction in cross section area of the pipe. As more taps/valves are opened, total flow will increase and create additional flow resistance, dropping the water pressure at each open outlet.

You mention replacing a gal feeder. This is normally done because the interior of the pipe has rusted and significantly reduced the cross section area of the pipe. I have come accross gal pipe which has clogged completely, and others that have reduced to 1/8 inch dia opening. Any significant closure of the pipe will affect water delivery. On that basis, I would establish a decent feed system before chasing anything else, as that alone might solve the problem

You have not been specific about the supply system, but the following assumes a high pressure supply supply rather than gravity feed from a local tank.

Mains HWS need a check valve on the inlet two stop hot water bleeding back into the cold, and a pressure/temperature relief valve venting to atmosphere via a pipe to prevent the unit exploding if the pressure or temp become excessive within the tank. If you live in a high water pressure area (low ground relative to storage dams etc), quite often a pressure limiting valve is installed in the feed pipe between the meter and the house. This reduces hot and cold feed pressures to avoid the mains pressure opening the PTR valve open all of the time.

The pressure limit valve can deteriorate with time and may provide additional flow impediment. In that case, replacing the unit is the only option. I seem to about 12 years from limit valves before they start becoming eratic and inducing water hammer at times (overpressure) or inhibiting flow.

It is common for hot tap pressure/flow to be lower than cold tap, because the HWS is often placed near the end of the cold water feed run, the valves needed, and plumbing the unit back to the outlets. In an installation with an ensuite near the front of the house, and the HWS toward the back, the cold taps in the ensuite most likely have the highest presssure because they connect nearest the feeder, while the hot taps have the lowest as the water is piped most of the way to the back, heated and piped back again.

If the plumbing is restrictive, drawing cold water at any point between the ensuite and HWS will reduce the feed pressure to the HWS and hence the hot outlets in the ensuite. Drawing hot water as well in the same location will split the available hot flow and the change would be more obvious at the ensuite as it at the end of the hot run.

Run 3/4" to all your fixtures and reduce to 1/2" as close to the fixture as you can, they do things differently in QLD and you'll probably find the whole HW installation is in 1/2".

Thanks

Originally Posted by malb

You mention replacing a gal feeder. This is normally done because the interior of the pipe has rusted and significantly reduced the cross section area of the pipe. I have come accross gal pipe which has clogged completely, and others that have reduced to 1/8 inch dia opening. Any significant closure of the pipe will affect water delivery.

Yep one small section just fell apart when I tried to unscrew it - confirming that the lot had best go. I was amazed water actually got through it.