Garavity Heating / hot water : Straddle Tank ?

bob_a_builder

The spec says with 0.1 bar should get 3L/min, but dont say its that hot,cold or mixed
On the mid position a quick unscientific test with couple of measuring jugs indicated about 4.5L/min

On the cold only get pretty close to 3L/m

Checking other bathroom, which still has single taps on 15mm pipes - but is a lot closer to the tank, getting 10L/min on the cold


"have you checked to make sure the limiter is actually set to maximum flow"
No - relied on factory default so far, but seems likely I'm getting the number the tap is capable of

Would like to retain 2 taps in the next bathroom , but all the built in furniture ( that I've found so far) that comes with a basin, comes with a single tap hole

MrBluesky_2

i am sure you have removed the aerator to check no debris is trapped and test the flow rate with it removed in case the incorrect aerator is fitted.
Hot water flow on monoblock basin taps gravity fed is always a gamble as the hot water has to push through a lot of resistance (cylinder) to reach the tap,cold feed is just pipework so always ok ish.
Other considerations are monoblock taps with rigid copper tails (not flexi) 15mm 1/2 inch feeds,i think yours are 3/8 inch,the flexi pipe should not be bent.
Also any isolation valves need to be full bore type and of course fully open,your main cold water tank could be on the small size you need at least 50 gallons with the fill level adjusted correctly.
Every property/installation will work differently,so people saying "our tap's work" are not adding anything helpful.

Good luck,

bob_a_builder

Flexis are really thin ! ...
http://imgur.com/a/FyjOv

EachPenny

MrBluesky wrote: »

Hot water flow on monoblock basin taps gravity fed is always a gamble as the hot water has to push through a lot of resistance (cylinder) to reach the tap,cold feed is just pipework so always ok ish.

Are you sure about this? If the cylinder is of the conventional type then all it is, in effect, is about a metre length of very large (say 600mm) diameter pipe. In practical terms, the resistance to flow of a hot water cylinder is virtually zero.

If the hot and cold pipe runs take approximately the same route between tank and appliance using the same pipe sizes then the resistance of the hot water run will be approximately the same as the cold water run. The inclusion of a length of 'large-bore pipe' will be balanced against the flow having to negotiate some additional bends.

MrBluesky_2

EachPenny wrote: »

Are you sure about this? If the cylinder is of the conventional type then all it is, in effect, is about a metre length of very large (say 600mm) diameter pipe. In practical terms, the resistance to flow of a hot water cylinder is virtually zero.

If the hot and cold pipe runs take approximately the same route between tank and appliance using the same pipe sizes then the resistance of the hot water run will be approximately the same as the cold water run. The inclusion of a length of 'large-bore pipe' will be balanced against the flow having to negotiate some additional bends.

Yes i am very sure about that,
would you like me to provide the flow rate calculation method ? Even the dozy teenagers i instructed the trade to understood about reduction of flow and pressure due to the effects of gravity or friction.
The above is a fact and !!!!!! not open to discussion.

bob_a_builder,your photo shows the severe reduction of pipe diameter,bent hoses and that type of isolation valve can only have one effect and that is reduced flow rate.

I have the pleasure of seeing so many defective plumbing,gas,electrical,building and lots of diy work,working as an expert witness :rotfl:

Wookey

If your water tank is effectively sitting on the ceiling joists the water pressure will be not more than .15 bar, add in length and routing of pipes this will decrease it by quite a bit, first thing i would look at it is to see about raising the cold water storage tank every metre you can raise this up will gain you .1 bar.

Changing the tank to a long rectangular one would allow you to get it up towards the ridge (assuming a normal pitched roof) and maybe as much as 2 metres in height.

The top joint on a hot water cylinder can (if its a tight 90) that has been installed for a long time will clog up with dirt and scale which will cause a serious flow restriction over time and would be worth replacing.

The other things that are mentioned in some of the other posts are worth checking out, certainly changing the taps to something more suitable if relocating the tank is out of the equation.

bob_a_builder

Other considerations are monoblock taps with rigid copper tails (not flexi) 15mm 1/2 inch feeds,i think yours are 3/8 inch,the flexi pipe should not be bent.

Is the consideration here to minimise the length of the thin part of the pipe
i.e an inch or 2 with the tails compared to about 10" of thin flexi ?
i.e.
Is the resistance increased as the length of the thin part increases or it a one off increase in resistance because of the diameter of the thin pipe ?

Can you choose to fit tails OR flexi on most monoblock taps ?

EachPenny

MrBluesky wrote: »

Yes i am very sure about that,
would you like me to provide the flow rate calculation method ? Even the dozy teenagers i instructed the trade to understood about reduction of flow and pressure due to the effects of gravity or friction.
The above is a fact and !!!!!! not open to discussion.

Yes please to seeing the flow rate calculation method, seems the professor who taught me hydraulic engineering must have been wrong.

Big pipe not much friction, small pipe lots of friction. What is there between the inlet and outlet of a hot water cylinder? (assuming it isn't full of scale of course).

EachPenny

bob_a_builder wrote: »

Is the consideration here to minimise the length of the thin part of the pipe
i.e an inch or 2 with the tails compared to about 10" of thin flexi ?
i.e.
Is the resistance increased as the length of the thin part increases or it a one off increase in resistance because of the diameter of the thin pipe ?

Yes, to maximise the flow rate you want to minimise the length of small bore pipes. In a dynamic situation (i.e. when the water is flowing) the whole length of the small bore will be contributing resistance to the flow.

An analogy would be thinking about a crowd trying to get into or out of a room through a pair of double doors. When the doors lead directly from the room to the outside the 'flow' of people will be greater than if the doors lead into a long corridor before you get outside. The longer the corridor the more the 'flow' will be reduced. If you've ever traveled on the London Underground in the rush hour you will be familiar with the effect

In my experience rigid copper tails are better because the reduction in bore is marginally less than typical for flexible ones. The flexible ones you have are long, hence the need to bend them, so you are getting the disadvantage of having both an excessive length of narrow bore pipe, plus the bends. It is better to select a shorter length and install them as close to straight as possible.

Rigid copper tails also generally taper from the larger bore size to the smaller one. This taper helps make the transition smoother and reduces the problems that an abrupt change of bore size can create.

MrBluesky_2

bob-a-builder,have a chat with the a plumbers merchants (give up google) they should be able to supply a monoblock tap and full bore iso valves to suit your water supply.It will slighty improve the flow.
Have seen this low flow situation many times and its usually due to incorrect fittings being used,also have been in discussion with a British tap maker re how they decide the minimum flow requirements. They explained the traditional requirement was a 2 storey house with a 50 gallon loft tank and the water tap being on the ground floor.got their pdf somewhere.

Off to visit a customer now who had a new boiler and bathroom fitted the water runs at a reduce flow rate but increased temperature rise,which has sadly hospitalised their son due to scalding.