Gravity fed shower issues

[gerbils]

We currently have an open vented / gravity fed system which we are imminently going to replace. Investigating Combis, Unvented etc has lead me to test our various pressures and flows and I have noticed an oddity.

Our mains is 12 Litres per Min
Our bath hot tap gushes out at approx 20 Litres a Min.
Our shower runs at 3 Litres Per Min.

I understand the water has a little further height to travel for the shower, and the shower head itself will reduce the flow a little but I suspect these numbers seem to be too far apart? Is there any way to get similar or maybe half of this flow rate into our shower?

 

[Johntheo5]

Is the shower a thermostatic mixer type or just a manual type mixer?
Remove the shower head and re measure the flowrate.
My gravity fed hot or cold 50 year old bath taps flow around 16/18LPM but these are 3/4" stopper type so basically a open pipe when fully open.

 

[gerbils]

They are thermostatic. I think they may be for Combi boilers... They were here when we moved in and have always been terrible. Shower #1 is 3 Litres a min and shower #2 is 1 Litre a min. Lol. I think that's limescale.

Removing the head does a make difference but only from 3l/min to 4L/min.

Is that standard for a gravity fed shower?!

 

[oldbuffer]

1. For a given pipe / outlet size, the flow rate is determined by the pressure pushing the flow.
2. For a conventional system (2 storeys, cold water storage cistern in loft, hot water cylinder in airing cupboard) pressure at the bathroom taps will be typically 0.16 at basin taps, 0.18 bar at bath taps and 0.06 bar at a raised shower head.
3. Also for a conventional system, the bath taps are likely to be supplied from 22 mm pipes, whereas basin is 15 mm.
4. So low pressure to all outlets. High flow to bath because of big pipes.

 

[MNW67]

I actually measured both of ours last night and was going to post about them on the other thread at some point.

With the shower head at its normal height, we get 6 litres per minute at the usual flow temperature.

Guests have always said how good our shower in the main bathroom is for a gravity shower. But there is nothing special about it. The bottom of the cold tank is about a metre above the attic floor. There is 22mm pipe all the way from the tank to the shower valve and the tank is immediately above the shower. The valve is a Trevi Therm from about 30 years ago.

I believe shower valves for combi boilers are designed to work at high pressure. Maybe they restrict flow in some way with low pressure feeds? That is just speculation!

 

[Johntheo5]

I'd say the "norm" for gravity fed showers is 3 to 4LPM, 6LPM is excellent IMO, Didn't Trevi make a venturi shower some years ago with cold fed mains and gravity fed hot which apparently gave something like your output?.

 

[MNW67]

I remember being shown something like that, but ours are bog standard Trevi Therms.

At the time, Trevi did claim that these standard Therms were particularly free flowing. The plumber told us they were based on a German design. No idea if that is true.

 

[Harry Bloomfield]

I believe shower valves for combi boilers are meant to work at high pressure. Maybe they restrict flow in some way with low pressure feeds? That is just speculation.

Correct, they do.

 

[MNW67]

I've just remembered, they were called Trevi Boost. But we definitely don't have them.

I've just been reading about these micro shower pumps which give a gentle boost. They seem to get very good reviews.

Easiest Way to Get the Perfect Shower | The Shower Power Booster

As seen on BBC Dragon’s Den. Compact pump for showers & taps. DIY fit with no electrician needed. Award-winning British design. Uses just 5% energy

showerpowerbooster.co.uk

 

[gerbils]

I've just remembered, they were called Trevi Boost. But we definitely don't have them.

I've just been reading about these micro shower pumps which give a gentle boost. They seem to get very good reviews.

Easiest Way to Get the Perfect Shower | The Shower Power Booster

As seen on BBC Dragon’s Den. Compact pump for showers & taps. DIY fit with no electrician needed. Award-winning British design. Uses just 5% energy

showerpowerbooster.co.uk

That’s so bizarre, I just saw those. Very good reviews on Trustpilot and very cheap

 

[MNW67]

That’s so bizarre, I just saw those. Very good reviews on Trustpilot and very cheap

That is bizarre

Do you know whether you have 22mm hot and cold feeds to the showers?

 

[gerbils]

That is bizarre

Do you know whether you have 22mm hot and cold feeds to the showers?

I have no idea. Would they be in the loft or airing cupboard?

 

[MNW67]

I have no idea. Would they be in the loft or airing cupboard?

I only know by comparing with the houses I've owned. We really need a professional.

I'm basically trying to work out why both my gravity showers give twice the flow of your better shower. The main variables are cold tank height above the shower head and the diameter of the pipes. Mine has 22mm hot and cold all the way to the shower valve and my cold tank is mounted about a metre off the attic floor. Is the whole shower valve mounted on the tiles or is just the knob visible? Are any pipes visible or are they buried in the wall? Do you know when the shower valves were fitted? My pipes are very easy to see because the shower backs on to the airing cupboard so I can actually see the pipes entering the shower valve from behind.

 

[gerbils]

I only know by comparing with the houses I've owned. We really need a professional.

I'm basically trying to work out why both my gravity showers give twice the flow of your better shower. The main variables are cold tank height above the shower head and the diameter of the pipes. Mine has 22mm hot and cold all the way to the shower valve and my cold tank is mounted about a metre off the attic floor. Is the whole shower valve mounted on the tiles or is just the knob visible? Are any pipes visible or are they buried in the wall? Do you know when the shower valves were fitted? My pipes are very easy to see because the shower backs on to the airing cupboard so I can actually see the pipes entering the shower valve from behind.

Our neighbour reckons his gravity fed shower is great too. The only difference they have is that they have only 1 cold water tank whereas we have 2. I think they shut one off for some reason.

They are very elderly and I assumed maybe they had a pump and didn’t realise but perhaps not …

 

[MNW67]

Our neighbour reckons his gravity fed shower is great too. The only difference they have is that they have only 1 cold water tank whereas we have 2. I think they shut one off for some reason.

They are very elderly and I assumed maybe they had a pump and didn’t realise but perhaps not …

Lots of people have been surprised how good ours is. I was thinking if you could get a flow a bit like ours and then add those micro pumps you might have what you want.