Flow washers are conventionally utilized in water discharging conduits in an effort to control the flow of water therethrough so as to make the flow volume more uniform under various or varying source pressure conditions. Such flow washers are frequently utilized under such varying conditions in combination with timers, in an effort to dispense a predetermined quantity of water where such is desired, as in washing machines. Since city water pressures vary between 15 p.s.i. and 120 p.s.i., the flow volume through a given valve will vary widely, absent such a flow washer.
https://patents.google.com/patent/US4592390A/en