Viscosity-Specific: Foam pumps are designed for specific liquid viscosities (thickness). Using a product that is too thin can cause dripping, while one that is too thick will not aerate properly and may clog the screen.
"Prime Time": A new or refilled pump requires a few presses to draw liquid up the dip tube and prime the mechanism before foam is produced.
Clogging: If not rinsed occasionally, product residue can dry and clog the very fine screens, leading to a weak spray instead of foam.
Orientation: Most are designed to work upright. Tilting or inverting the bottle will break the suction of the dip tube.