A finger-operated spray pump assembly including a tank, a primary piston slidably fitted inside the tank, a secondary piston slidably fitted inside the primary piston, and a spring fitted inside the primary piston and on the outside of the secondary piston for biasing the primary piston away from the...http://www.google.es/patents/US4154374?utm_source=gb-gplus-sharePatente US4154374 - Finger operated spray pump
