Gravity Water Flow

[chiangrai]

I have a gravity water flow source..It's a tank made of 4 concrete rings on a slope about 20 feet above the house.

It has a half inch PVC pipe coming out of it as the only out pipe and has good pressure.

So I plumed a tap up to it in the bathroom and that had good pressure.

Then I carried on and brought the pipe up and down again to the shower which is about 12 feet away but the pressure was really week when I finished it.

It's a small gas shower and there was not enough pressure it .

How did I loose this pressure.I thought that going up.was not a problem if you go down again to the same level..Was it the 90 degree bends that did it,there was a lot of them.

I saw some 90 degree PVC pipe connectors in the hardware shop that were light brown and curved instead of angular and blue like the ones I used.

Would changing to them increase the pressure.

Or should I replace the half inch pile coming out of the tank for a bigger one.

If so how would I bring it down the slope without stepping it with 90 degree connectors.

[cooked]

I'm guessing that you have an air lock at the highest point. The shape of the joints will have a very minor influence on water pressure. Radiators in cold climates need to be 'bled'. Work out how tp do it with your setup.

[bankruatsteve]

If not too much trouble/expense, you should go with at least 1" PVC from the tank to house connection.

[chiangrai]

Ok,so if minimum 1 inch pipe at the tank what;s the maximum and

is there some type of a flexible pipe I can attach to it like a hosepipe

so as to bring it down the slope.

Don't know how I would bleed it.

[STMx]

Shower is higher than bath so the pressure is lower. Modern showers need at least 2-3 m of water pressure.

[canopy]

As others say, up sizing your pipes is a good idea. Less pipe friction means you'll get more flow and also can run more than one tap in parallel. But it won't solve this particular issue. The problem is internally shower heaters send water through tiny pipes inside, way smaller than half inch. You could use a demand pump or replace the gas heater with a solar water heater that doesn't reduce the pipe size.

[bankruatsteve]

Your tank likely has 1" outlet so using larger pipe might help as additional reservoir down the slope but at constant flow would be restricted by the 1". You say you went "up and down" for the second shower. What exactly did you do? IE: for every up that you went will negate the gravity pressure correspondingly after that. Could be your 2nd shower is effectively just siphoning.

[sometimewoodworker]

If you can keep all the pipe in large bore pipe all the way to the water heater you will have better pressure.

Any length of small bore will reduce the pressure, the longer the run the lower the pressure. Also all sharp 90 degree bends reduce the pressure.

If you have a pump the pressure reductions may not be very significant but with gravity feed they are much more noticeable.

[chiangrai]

Thanks Sometimewoodworker,

Have you seen the beige colored pvc pipe connectors

with rounded 90 degree bends as opposed to the blue ones with sharp 90 degree bends.

Do they reduce the pressure less.

Do you know a good type of hose to bring the water down from the slope

or should I use pvc pipe.I want to berry it.

Is there any point in using a pipe bigger than 1 inch coming from the tank,

maybe as far as the bottom of the slope.

[NamH2O]

This should explain all yu need to know about Gravity Feed.

The water pressure available in a gravity-tank fed system is directly related to the height of the cold water storage tank. To calculate the available pressure simply measure the distance, in metres, from the bottom of the cold water tank to the outlet of the tap or shower and multiply by 0.1 - this will calculate the pressure in bar...

for example : 0.1 bar (1.45 psi) is equal to approx one metre of height between the bottom of the water tank and the outlet of the tap or shower.

1 metre height of water = 0.1 bar

2 metre height of water = 0.2 bar

3 metre height of water = 0.3 bar

4 metre height of water = 0.4 bar

etc

in the example opposite

The shower outlet will have a water pressure of 0.1 bar

and the kitchen tap will have a water pressure of 0.5 bar

So to achieve even 1.0 bar of water pressure from gravity fed hot water systems you would need to have a cold water header tank in the loft which is 10 metres above the height of the tap you are using, clearly this is not possible in most homes.

Mains pressure: This is the pressure of the water supply entering the house measured from the stop tap. Water companies will maintain a minimum requirement of 1 bar water pressure, and a flow rate of around 9 litres per minute.

Water pressure is often confused with water flow but they are not the same. To understand the difference between water pressure and water flow click here

[happynthailand]

if it was me i would install a small water pump close to the house

problem solved

[sappersrest]

Nam H2O.

great post, well explained.

[sipi]

Yes, as NamH2O explained, for every 10 metres you gain 1 atmosphere (101.4 kPa/ 14.7psi approx) of pressure. The first rule of scuba diving.

[sometimewoodworker]

Thanks Sometimewoodworker,

Have you seen the beige colored pvc pipe connectors

with rounded 90 degree bends as opposed to the blue ones with sharp 90 degree bends.

Do they reduce the pressure less.

Do you know a good type of hose to bring the water down from the slope

or should I use pvc pipe.I want to berry it.

Is there any point in using a pipe bigger than 1 inch coming from the tank,

maybe as far as the bottom of the slope.

As to slow bends, sorry no. But the more gradual the change of direction the better.

LDPE or HDPE pipe is probably a good bet for low pressure use and it comes in 50metre lengths, and is quite cheap.

Bigger is always better for low pressure use if it's possible to use it. There will be a point where the increase of size makes no significant difference. To know where that point is you need someone far more qualified than I am.

[Gandtee]

if it was me i would install a small water pump close to the house

problem solved

I disagree. Yes the problem solved, but you have the cost of the pump and the cost of running it. Maybe the likelihood of power failures also. I'd just go for a small release valve at the top of the loop to bleed the air occasionally as the problem seems to be an airlock.

I installed a tank in the roof space which supplies an electric shower and domestic water. It's barely 3m above the shower. The old shower worked perfectly until it failed due to old age( a bit like me) The new one failed to work. I removed the water control valve which came with the shower and it works perfectly.