It is the speed at which a liquid flows and is measured in gallons or liters per minute. Flow rate of a liquid can be affected by the liquids’ A resistance to flow as a function of force, or gradual yielding of force. Viscosity is in units of centipoises or centistokes. For a given filter and differential pressure, flow rate will decrease as viscosity increases; e.g. oil will have a flow rate much slower than water. The viscosity of water is 1 centipoise...., differential pressure, temperature and type of filter used.