What sort of flow should I expect with two showers?

[zog]

I have a mains pressure hot water system and two first floor bathrooms with showers. When one is used at a time, the flow is just fine - each shower is a Grohe thermostatic. When two are used (and no taps/washing machines/toilets flushing) the flow is quite seriously reduced to a point where you have to move almost directly under the shower to get any water. Its usable, but only just.

I've checked the inlet - we had installed a new stop cock, fully open.

When the pressure was measured by the water board about 4 months back I think he said it was around 4 bar - that seemed pretty high to me.

Am I expecting too much here? I know I can't attach a pump to the mains ... is there any other way I might up the pressure so two people can shower at once? I am about 100 ft from the main road where the roadside stopcock is located. Is there a chance the link from there to me is bad or too narrow? House is about 50 yrs old.

Mike

 

[hi-spec plumbing heating]

what is the hot water system your running from ? combi boiler etc make model.

 

[zog]

The boiler is a unvented Vaillant ecoTech plus 630 - its a system boiler (if that's the right term), not a combi and its currently at 1.5 bar idle, and the cylinder is a 200L Tempest Stainless steel version, pretty much like Vantage or Heatrae. I used to have a standard HW cylinder 150L on the first floor fed of a Mexico I, ancient model, but changed the boiler and hot water storage (they call it heat store now I think) at the same time about 2 months back.

 

[baxpoti]

If you now have no 'stored water' eg your system is mains pressurized, then you only have the incoming supply, which is split between the showers.

What is the maximum cold flow rate measured at the kitchen sink?

 

[ChrisR]

What is the maximum cold flow rate measured at the kitchen sink?

Might be worth putting the garden tap on at the same time and combining the two figures. Some kitchen taps ...!

This could be a suitable appication for an Accumulator. Which is a water store with a big bag of air which gets squashed to mains pressure. When you draw water it pushes water out from its store. I haven't explained that very well.
Disadvantages are size, cost. and volume/pressure limit.
If you had a tank in the loft you could pump from that into your Unvented cylinder.
But you need a loft, and pumps make a noise.

 

[zog]

I don't know the flow rate just yet - water board coming on Tuesday to check at house entry and at road.

Wow. I was going to ask about the Accumulator but then spending a bit more search time... I see Chris et al have provided loads on it. THANKS. I am wondering whether changing the pipe from the road to my house (about 100ft - I am well set back) would make more difference. Probably costa a bomb though.

I'll see when I know the pressure at the road and my house I guess.

The house was built in the 50's but I have no idea what's down there. I'm looking for two showers running normally when turned on at the same time. They aren't power showers, but are mains connected. My internal pipework is OK I think - looks new copper pipes, and certainly when the heating was replaced all of the pipes for the showers were replaced.

Mike

 

[emphasis303]

Hi

got the same problem, got a vaillant 630e with an ariston indirect unvented cylinder and two showers at the same time are a bit of a problem, but apparently this is expected by the manufacture ive been told, but this could just be an excuse, I was told to check the inlet into the cylinder from the mains to make sure it was opened enough but not to touch it myself but only by a plumber.

 

[Slugbabydotcom]

There should be a filter on the mains supply to your UV cylinder. Has it been cleaned lately?
Is your mains stoptap fully open?
Is there anything else that might cause a restriction in the line?

 

[bengasman]

Pressure if of little importance here, it is a matter of flow. Your pipes are either too small or there is a half open valve somewhere between the cylinder and the main valve

 

[zog]

The stop cock is brand new and fully open (minus a qtr turn). WRT flow and pipe sizes - what would you expect to see as pipe diameters at the stop cock or elsewhere? Should there be any difference within the house itself?

Does this mean that most people who have mains pressure systems don't experience any drop in flow if two showers are turned on rather than one ?

 

[lagunaglen]

If its unvented you should have a 22mm supply from stop tap to the cylinder and ideally a balanced cold supply to all the showers, this comes off the cold water combination valve .

 

[ChrisR]

Does this mean that most people who have mains pressure systems don't experience any drop in flow if two showers are turned on rather than one ?

Sadly, a lot stick to the old 1/2" mains pipe, in best squashed lead, and suffer the consequences!

 

[zog]

OK - had my visit by the water board ... the pressure at my outside tap is approx 2.8 bar, which makes sense as my unvented system is pressure limited to 3 bar. However, the flow rate is only 10 liters/min.

When measures at the roadside ... the pressure is 5.6 bar! And .. the flow rate was greater than 50 L /min (the measuring can was overflowing).

So it seems the pipe from the road to my house is too small in bore (its carbonised steel below my stop tap, allegedly). Or, has a kink in it as its pretty old.

My internal stop tap has 22mm copper. Hopefully, there's an easier way to mole-bore a new pipe rather than dig the entire drive and entrance up to the stop tap.

 

[zog]

Just a follow up in case it helps anyone else. The distance from the road edge to the house is unfortunately... 60m. Its because there is a long shared drive and I'm at the end of it.

Average cost of sending a mole down to replace with 32mm plastic ... £1500!

Ouch.