It is easy to confuse the volume and effective volume of a pressure tank. To put it simply, it refers to the difference in the volume of water contained in the pressure tank's airbag after the system is installed, when the system is running, and when it is not running under static pressure. For example, if the volume of water in the airbag is 100L after the system is running and 20L in the static pressure state, Then the effective volume is 100-20=80 liters.
The effective volume of Aquafill pressure tanks is directly related to the working conditions and the size of the pre-charging pressure. For pressure tanks of the same volume, the effective volume varies under different working conditions or different pre-charging pressures. There are also slight differences in closed-cycle systems and constant pressure systems, but it is basically calculated based on PV= constant value. For example:
In a closed-cycle system, to increase the effective volume of the Aquafill pressure tank, the pre-charging pressure of the pressure tank is generally set to be consistent with the static pressure of the system. Since the working medium pressure of the system is the same as the pre-charging pressure, the working medium just cannot enter the airbag at this time. When the system starts to operate, the maximum amount of working medium that can be absorbed in the airbag depends on the take-off pressure of the system safety valve. Because the pressure always goes to the easiest place. When the safety valve starts to release pressure, since the pressure relief port is directly connected to the atmosphere, the medium no longer enters the airbag. Assuming that the static pressure of the system and the pre-charge pressure of the pressure tank are both 1.5bar, The take-off pressure of the system safety valve is 6bar, and the total volume of the pressure tank is 100 L. The effective volume is calculated as follows when PV= is fixed:
P0*V0=P1*V1 V1= P0*V0/P1
P0=1.5bar, V0=100L(ignoring the volume of the airbag, the volume of the pre-filled gas is equal to the volume of the tank), P1=6bar
V1= P0*V0/P1=1.5*100/6=25L
When the safety valve is about to release pressure, the volume of the pre-filled gas between the Aquafill pressure tank airbag and the tank body is compressed to only 25L. Therefore, the volume of the working medium in the airbag is equal to the volume of the tank minus the volume of the pre-filled gas, that is, 100-25=75L. From the above calculation process, it can be known that when the take-off pressure of the system safety valve is different, the effective volume will also be different. By the same principle, if the precharge pressure is not the same as the system static pressure, the result will also be different.
In a constant pressure system, to maximize the effective volume of the Aquafill pressure tank, the starting pressure of the water pump is generally set to be consistent with the pre-charging pressure of the pressure tank. In this way, when the system is short of water, all the water in the pressure tank airbag is replenished to the system, and the water pump just starts to start, avoiding the situation where the water in the pressure tank airbag has not been utilized before the water pump starts. The stop pressure of a water pump is equivalent to the lift pressure of a safety valve in a closed-cycle system. The calculation process is similar to the above. Therefore, the pre-charge pressure, start pressure, and stop pressure are different. For pressure tanks of the same size, the effective volume is not the same. Thus, blindly marking the effective volume on the pressure tank is incorrect.
