Why Press the PET spray bottle twice before use it?
When the liquid starts to be drawn, the trigger starts a downward stroke instead of the upward stroke (the piston is outside the hydraulic chamber). When the wrench is pulled back for the first time, the piston is pushed in but no liquid is drawn out; there is only air in the hydraulic chamber. The piston slides out of itself to suck liquid from the reservoir.
When the PET spray bottle piston begins the first upward stroke, the pump begins to draw cleaning fluid from the reservoir. But at the same time, it sucks up the air in the plastic pipe that connects to the reservoir. Before you start spraying the cleaning solution, use the pump mechanism to remove the air. Therefore, it may be necessary to flip the wrench back and forth several times.
This simple pump design is called a reciprocating piston pump and has a wide range of applications. In addition to pressing water, air and other liquids, this design can also be used to extract water and oil from the ground.
There are also reciprocating pump systems in the human body: When the heart is dilated, low pressure blood is inhaled through a one-way valve; when the heart contracts, high pressure blood is forced back into your body from the other one-way valve.
