gravity flow

[Richard Condon]

Can gravity flow work in a circular motion ? e.g. 28mm flow rising from stove accross ceiling down through cyl coil and return to stove under floor I know that this system has to be vented properly. I could fully pump as an alternative as the cylinder is about 5 m from boiler. I have plumbed similar when cyl is nearer boiler on platform or upstairs with a rise on flow and return and pipe stat to power pump for heating.
I usually run rising flow from cooker / stove to cylinder in 28mm and a direct 28mm expansion to f&e tank. I think expansion can happen through cold feed also. I put 3bar safety valves on all boilers that i install

 

[ShaunCorbs]

Yes the flow must always rise

 

[Richard Condon]

Hello all, I am a time served plumber with a lot of experience. I worked for a local plumbing company in Tipperary Ireland in '85 - 86 and then moved to London where I worked for companys there and also self employed. I worked in London for 14 years. In Ireland we still use imperial sizes e.g. 15mm copper is 1/2", 22mm copper is 3/4" and 28mm is 1". Also here in Ireland we use number codes for fittings, whereas the UK system describes the fittings e.g. male iron to copper etc.

Of course there is no solid fuel systems in The London area which leads me onto my query regarding gravity flow systems to solid fuel stoves.

I have plumbed many solid fuel stoves / cookers where the cylinder is near the stove, the cylinder can be put on a low platform to allow for a rise in the pipework to facilitate gravity flow. It is similar also if cylinder is nearby upstairs. The 1" or 28mm flow pipe can then be continued without any obstructions eg valves etc over the F&E tank as the expansion. The system can also vent through the unobstructed cold feed also fit 3 bar safety valve. When the heat goes on the gravity heats DHW, a pipe stat is fitted to the flow which powers the pump and heats the radiators

QUERY:

My stove is in Kitchen (bungalow) and the cylinder is 6M across floor. Its in my head that you can get gravity flow to work in a circular motion eg take 28mm flow from stove, up, accross ceiling void, down through cylinder coil and back under floor.

Of course I can fully pump both circuits, which will solve it, But i would love to know if it is possible to gat Gravity Flow Working in this way

 

[Chuck]

My stove is in Kitchen (bungalow) and the cylinder is 6M across floor. Its in my head that you can get gravity flow to work in a circular motion eg take 28mm flow from stove, up, accross ceiling void, down through cylinder coil and back under floor.

In theory, this won't work because the head driving circulation around a gravity system is proportional to the height of the dissipating elements (your cylinder coil) above the boiler, which is zero.

Even in cases where gravity systems might be okay I'd rather have a fully pumped system because I don't like cold baths...

 

[John.g]

Yes the flow must always rise

One would think so yes but the maxipod thermal store shows the flow rising up, then down to the cylinder, I wonder does this increase the mean circulating height between the boiler and cylinder or just helps to prevent reverse circulation.

 

[chris watkins]

The gravity circulating head can be calculated if you know the head (height between flow & return), length of pipe run & the fittings to be used.

It is all about the frictional resistance so if you can use pulled bends &/or swept fittings this will help greatly.

 

[John.g]

And the greater the circulating height, the greater the circulating force. (circulating height is the mean distance between the boiler/stove flow&return and the cylinder flow&return,
I took these temperature readings (cold cylinder) many years ago from a stove where the cylinder was ~ 15 ft above the stove, if the calcs are anyway accurate it just shows how small the circulating force is, 0.008M in this case and as you say, how important it is to have as low a frictional resistance as possible with proper fittings and piping diameters.

Circulating head in M/M(Height)= (difference in densities)/((mean density)
Temp/density​	40C​	992.21kgs/m3​		Cal Flow​	1.1​	LPM​
Temp/density​	55C​	985.69kgs/m3		Energy​	1.15​	Kwh​
Circ Height​	5​	M
Circ Force​	0.008​	M	0.32​	ins