Pressure and leak testing a vessel
NEVER pressure or leak test a vessel with air or other compressible gas. NEVER!
Even at low pressure, a moderate volume of compressed air or gas can store an enormous amount of energy, and if your vessel should fail, that energy can be released violenty, with enough force to kill or seriously injure you or bystanders.
A much safer way to pressure test a vessel is to fill it with water. Make certain there are no pockets of air trapped in the vessel.
Water is much safer than air or gas, because it does not compress, so cannot store much energy under pressure. If your vessel does fail, there will simply be a release of liquid onto the floor.
It is also easier to locate a leak with water, rather than air, because you can see where the water is leaking from, and you don't need to use a pressure gauge to detect a drop in pressure, just look for drips or a puddle on the floor!
First fill the vessel with water, ensure there are no pockets of air and that all pipework is full of water too. Connect a vertical pipe to the top of the tank, and have a funnel in the top of that pipe.
Don't connect your water supply hose directly to the tank, just pour water in through the funnel.
The pressure in your tank will depend on the total height of water. Every 12 inches / 30cm of pipe will add around 0.5psi / 30mbar of pressure. So a 30 foot / 10 metre height of pipe will have a pressure of around 15psi / 1 bar at its bottom.
There are not many reasons why you would need to pressure test a tank for biodiesel processing anyway, as you can generally run the whole process at atmospheric pressure.
The only reason for a pressure test in a homebrew biodiesel processor may be to reveal leaks, but as the processor will be running at atmospheric pressure, you won't need to pressurise the tank beyond the pressure caused by the liquid in the tank itself.
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