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The advantages of a home-made pressureless tank, in our purpose of accumulator in a solar boiler, can go unnoticed.
As it is not subjected to pressure, it is easy to use plastic tanks.
Although you can also use any type of material in this format.
It should also be said that a metal tank exposed to the air will rust quickly.
Although it is true that plastic is not specially designed to withstand high temperatures, up to a certain limit it can do it perfectly.
The home-made pressureless tank is a very good and very economical solution.
As long as it is a well-built and well-insulated tank, as is the case with the Building a gravity water tank for a homemade solar heater homemade manufacture of my own tank.
The solar heater application tank can be of 2 types.
My project to build a homemade solar heater is based on a depressurized tank, and its material is food-grade plastic.
In order to be able to use the homemade pressureless tank in the shower and taps, I have installed the tank on my roof (about 6 meters high)
As for the material, I am going to make a practical comparison between the "pressurized tank" and the "depressurized tank" (also known as gravity tank)
I always mention the pressure tank first in this list, and the other way around second.
A pressure tank, usually made of metal, is complex to manufacture at home, and can be expensive.
The pressureless tank, if homemade, will be conveniently made of plastic for ease of handling and use.
The pressure tank must inevitably be made of metal.
A metal tank is difficult to build at home.
A tank recovered from a waste site will be in a sorry state.
The pressureless gravity tank can perfectly be made of plastic.
It is easy to acquire very economical plastic tanks in perfect condition.
The pressure tank cannot be opened.
To check its interior, the first thing to do is to isolate it from the pressure circuit and empty it.
As there is no pressure or tightness, the gravity tank can be opened even when it is in service and working.
The steel of the tank is attacked by several factors, high temperature, high pressure.
Glavanic corrosion can occur due to the use of metal with copper. All of them need a special device to prolong its life.
This device is usually an electronic anode, or physical magnesium anode that deteriorates in a few years.
The home-made pressureless tank, or gravity tank, if it is made of plastic, will not need any type of maintenance.
Long-term visual supervision is sufficient.
The pressurized tank directly receives the pressure of the water in the home.
It must be able to withstand this pressure, which is usually between 4 or 5 bars.
But even this pressure can grow more when the accumulated water increases in temperature. (High temperature also increases pressure)
So that we are going to need a diaphragm to be able to withstand this increase in pressure.
And we also need to install a safety valve.
Apart from the risks of leaks and breakages typical of high pressure in elbows and unions, there is also the risk of maintenance and deterioration of the devices mentioned above.
In the depressurized tank, the unions and elbows do not need a strong and perfect seal.
The tubes can be simple hoses.
There is no type of danger related to high pressures.
A leak through a pore will be less serious than in a high pressure system.
In a pressurized tank, the water flow is moved by the pressure itself.
That is, we open a tap, and the water comes out with the same force as it enters. (In reality, a pressurized tank is like a large pipe)
We can put it anywhere. As if we buried it under the ground.
In the non-pressurized tank, the water output will be supplied by gravity.
So it must be placed at a high point.
Any tap that is at the same height as the tank or above it will not draw water.
In this case you will need a water pump. And this involves costs.
In the pressure-sealed tank, if the general water supply to the house stops, the tank will not allow the water to escape.
In the non-pressurized home tank, by its very nature, we can consume its contents even if there is no water inlet.
If there is no water inlet, the non-sealed tank will only stop supplying us when its stored content runs out.
A pressure tank, as I said before, is like a giant pipe.
Therefore, every time a tap is opened, for every drop of hot water that comes out, a drop of cold water enters.
In other words, consuming 20 liters of stored water means refilling another 20 liters of cold water and mixing the contents.
This means that the water is mixed at the rate at which it is consumed.
And if the incoming water is very cold, it will reduce noticeably and quickly the energy accumulated in the tank.
(Some will not notice it and will not be aware, because they use electrical resistances to support to heat the water, at the expense of the electric bill)
The pressureless tank, the processes of water inlet and outlet can be isolated.
We can have any mechanism that fills the tank in a way conditioned by the factors that interest us.
Even if I have 300 liters of warm water before a bad storm, I can close the inlet valve.
Do you know what this means? Well, 300 liters of water that will not mix, and will come out until its last drop at its stored temperature.
In a pressure tank, the water capacity is determined by the size of the tank itself.
That is, you cannot buy a 300 litre tank, and then adapt it so that it does not store more than 100 litres.
Another problem is the difference in stationary performance.
In other words, it may be small in summer and large in winter.
The pressureless tank is ideal for this purpose.
As it is not airtight, you can decide to use a large part of it, or a small part.
With a simple filling valve with a float, you can define how full it is.
In winter you can convert a 300 litre tank into a 100 litre accumulator. (The less water, the faster it heats up)
And in summer you can use its full capacity to prevent temperatures from being excessively high.
A typical standard, sealed and pressurized solar thermal installation is supported by several safety devices.
Devices that are taken to the extreme, sometimes failing and literally bursting the system.
They burst because the water has nowhere to escape. It is an overpressure problem.
This is the main reason for so many broken solar thermal installations and their clogged screens.
If there is one thing I can boast about with my home-made pressureless tank in my solar thermal use, it is that I have no risk of overpressure.
What happens in an excess of temperature and pressure:
The water does not harm anything because it has infinite space to occupy (if it exceeds the space of the accumulator, it will spill outside)
The water relaxes its temperature naturally through the steam that will come out through the vent.
The steam releases excess energy.
It will do so through the vent that we provide, and if there is none, it will do so through non-airtight spaces.
Pressurized sealed tank. What can we say? It will depend on its safety systems (diaphragms and valves), or the use of an electric resistor, which will save the inevitable bursting of the installation.
When water freezes, it also expands, and needs extra space.
The pressureless tank.
If freezing does not occur very very quickly, the water will easily find plenty of space to expand.
The space is free in the tank itself.
It seems that the depressurized tank wins by a landslide.
The home-made pressureless tank only limps in one point.
Although this point is a very critical and very important point.
As the pressure of the water coming from the street is lost when filling the tank, we have to come up with something so that the outlet is able to reach our taps, and that the flow and pressure is more or less generous.
I have already built my solar heater with a pressure tank in the past, and the results were very good.
But I had constant problems with water leaks, and at the same time a pore in the tank...
It was an 80 litre tank, and despite the small storage and consumption system, it was not very efficient.
So I opted for the home-made pressure-free tank, for the advantages I have mentioned.
The truth is that the result has been excellent.
And despite doubts about its resistance and lifespan, I have been using it since 2010 without problems.
This is the diagram of the tank with its mechanical components: (The numbers are the measurements I use on the accessories)
This is the vent for the home tank.
When water enters faster than the water leaving, or enters without leaving, the difference in air pressure comes out through here.
(And vice versa)
Even though the air entering may be cold, it does not seem to have much of an effect.
In this vent tube, water also evaporates naturally when its temperature is excessive.
This is the water inlet device (cold water).
It has the same mechanism as that of a washbasin cistern.
Here we can configure the height of the floating body, which will be the maximum water height level.
This is the point discussed above about convenience depending on stationary time.
The tube that carries this water to the bottom, which is where the coldest water is in the tank.
A non-return valve is added to this connector (the grey box with a black arrow), to force the direction of the water and prevent it from going back.
This is the water outlet device (hot water).
The so-called fishing tube. Its function is to float and suck the water from the top (warmest part)
It must be this way because in this tank the water level is continuously variable, it is not possible to make an outlet at a fixed and specific height.
The fishing tube must be a flexible tube that does not harden with time or heat.
The tube will remain attached to a floating body, I use a small empty bottle. (an aluminum canister can be used)
The fishing tube will be in charge of to chase the upper water level, always collecting water without air, and from the warmest part of the tank.
You can add a stopcock to this connector (the red stopcock), to stop the imminent emptying in case of a breakdown.
At the bottom of the tank I put a plastic mesh, to prevent the fishing tube from reaching the bottom.
I do this as a precaution in case there is lime or residue at the bottom.
Since there is no natural pressure to flood all our tubes, in case of having tube C empty, we will need a manual «start» action.
Why?
Simply if tube C is not full of water, there will be nothing to suck the water from the tank.
It is the water that goes down that makes it suck and «stretch» from the water in the tank.
This action can be the suction of tube C (we can even suck it with our mouth)
We can also do it by connecting a garden hose or tap to tube C.
So that the domestic water pressure fills the entire conduit C.
A trick to fill the “C” tube from home without intervening or dismantling anything.
It all consists of half opening a tap.
Home taps open 2 circuits, the cold water circuit and the hot water circuit.
In an intermediate position, it opens both outlets to mix their flows. (what we would do to obtain warm water)
Ok. Well, in this mixing position, we physically cover the mouth of the tap itself.
By blocking the cold water that comes out, it will flow through the hot water conduit. (The hot pipe rises to our home tank without pressure)
Since this pipe is empty and our tank has no pressure and does not offer resistance, the water will rise.
The pipe C will fill up and the air bubbles will come out freely inside the tank.
And that's it, after a while we will simply open the hot water and see if the water output remains for a while to indicate that the tank is giving its flow.
Once we consider the pipe “C” full of water and without air, we consume a considerable amount of this water.
If the water comes out and does not stop in a certain time, it means that the pipe “C” is in service and ready for use.
enthusiast with two decades of experience using this operating system, which has enriched my approach to development and technical problem solving. 
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, with approximately three years of experience in 
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, combining my skills with a deep passion for technology. 
environments, which I use in all my programming projects.