Maximizing Water Volume from 50L Diaphragm Pressure Tank with 1.5-3 Bar Pressure Switch Range

Hello,

I have a 50 l diaphragm pressure tank. A pump with a pressure switch is connected to this tank - which pumps water in the range of 1.5 bar (on) - 3 bar (off). The pressure in the tank membrane is preset to 1.5 bar. After repeated attempts to pour water into the bucket, no more than max. 12-13 l comes out to restart the pump. I have the following question:

What can theoretically and practically be the volume of water received without switching the pump on again? It seems to me that the value about which I wrote above is too small.

I would add that I tried with different diaphragm pressure settings from 0.8 to 2 bar and this 1.5 bar seems to be the most appropriate in this situation. The tank is new.

Am I doing something wrong?

wojtas_master wrote:

Am I doing something wrong?

Yes. Looking for a "hole in the whole". Any hydrophore tank is not a canister from which we will collect all the liquid previously poured into it. Only 1 / 4-1 / 3 of water from its total capacity is taken from each hydrophore. These are the laws of physics and nothing will change that.

I'm not looking for a hole in the whole, just a normal answer. I once read somewhere that the actual capacity should be around 50% of the tank, hence my question. In my case it is 24% or half less than what I assumed.

If

wojtas_master wrote:

I tried with different diaphragm pressure settings from 0.8 to 2 bar and also 1.5 bar

You yourself noticed that the water intake did not differ much. You will take the most water, with a large differential pressure on-off. The smaller this water difference is charged to me.

wojtas_master wrote:

I'm not looking for a hole in the whole, just a normal answer. I once read somewhere that the actual capacity should be around 50% of the tank, hence my question. In my case it is 24% or half less than what I assumed.

Of course you are not looking for a hole. A simple question, but not everyone knows the answer. I honestly don't think so either, but it may be that this low capacity is due to the existence of an airbag over water. Please note that this tank works like this. At the beginning it is completely empty and above the diaphragm you create a pressure of say 1.5 bar. Then the diaphragm bends to the water side. You've already inflated it, screw the tank to the system and start pumping water. The main question is whether the water will take up the entire volume under the diaphragm or not. If it doesn't, because part of it will take air, then you will naturally get a smaller water volume, because even though compressed air over the water takes some space - although I have no idea if it will be a volume of 1 liter or 10 liters. According to me, the tank should be vented from the water side, i.e. the air should only be above the diaphragm and only water under the diaphragm. In my opinion, a useful amount of water from a tank of about 50 L will be about 25-30 liters. Please note that if you had properly pre-inflated the tank with air, after pressing the water, the pressure should be enough to push out the entire volume of water. However, this pressure will decrease up to 0 bar - as all the injected water flies out. However, you need to pump water between e.g. 1.5 and 3 bars, so this means that you will not be able to use half the tank volume, but less (although, in my opinion, you should be able to pump more than 25 liters of water into a 50 liter expansion tank). You would have to use a higher inlet pressure and thus pump water for a higher pressure to be able to get more water with one pump start.
For example, I have a 300-liter classic tank, without a diaphragm. Initial pressure of about 1.7 bar and then load the water with the pump to about 3.5 bar. The switch-off threshold is at 1.3 bar (for 1 bar water is not flowing too well up from the basement).
I used to check it a long time ago and managed to pour out about 70 liters of water in this condition, i.e. 6-7 buckets. It's a bit small for a 300 liter tank.

^ToM^ wrote:

For example, I have a 300-liter classic tank, without a diaphragm. Initial pressure of about 1.7 bar and then load the water with the pump to about 3.5 bar. The switch-off threshold is at 1.3 bar (for 1 bar water is not flowing too well up from the basement).
I used to check it a long time ago and managed to pour out about 70 liters of water in this condition, i.e. 6-7 buckets. It's a bit small for a 300 liter tank.

And you will not achieve more. From this it follows that you download about 1/3 of the tank capacity. And I gave such an answer.

^ToM^ wrote:

You would have to use a higher pre-pressure and thus pump water for a higher pressure to be able to get more water with one pump start

Only that it won't change much, not much more water for collection. Everyone would like to take a lot of water and buy the tank as little as possible.

You will not get more if you have 12 13 l is max. maybe 15l but that's all and the game is not worth the candle. And the fact that you read that 50% of the volume is probably an advertising gimmick for those who are at odds with physics. Perhaps it is possible, but when pumping the max. Pressure of the tank and for pouring into a slow spout without pressure, and probably the tank would still have to be set with the drain down. That's it for me.

Thank you for your answers, I now know that it should be calculated in the future. Fortunately, such a tank as I bought did not cost a fortune (PLN 105) so it is ok. Its use will be for watering the garden and household work, so the nuisance of frequent switching on will not be significant compared to typical home work - in a washing installation, etc.

The largest working capacity will be obtained when the diaphragm is at 0 pressure (valve unscrewed). The problem is whether, under water pressure, the diaphragm will stretch to the entire tank and rupture. We do not know the strength of the rubber diaphragm.

>>21223141 You are writing nonsense. In this case, you inflate the water to the diaphragm, make the pressure (with a pump) and take a few litres of water, or even less, because the water is not compressible.You don't understand how it works.

When I drained the water from a pressure of 4 atm. to 0, about 15 litres flowed out. (diaphragm pressure 2 at). The tank is definitely more than 15 litres, probably 50.

obatelgrzegorz wrote:

The highest working capacity will be obtained when the diaphragm is at pressure 0 (valve unscrewed)

.
If you leave the valve unscrewed you will inflate the entire water tank and there will be no pressure to collect the water.
The diaphragm acts to isolate the water from the tank and the air( so that it doesn't dissolve in the water and pump less often).
There must be some initial pressure to use the collected water in the tank. The larger the air cushion, the more water you will use, but it will not be 100% of the tank capacity.

The useful capacity is simple to calculate.
V(useful)=V(total)*(1-P_bottom/P_top), pressures in absolute value.
This applies to tanks with and without a diaphragm.