The invention discloses an electric
water heater provided with a
water flow sensor and a blow-molded water tank and capable of realizing external
semiconductor or
optical energy heating. The water tank 8 is made of a non-metallic material with an injection molding technology; the
water flow sensor 4 is mounted on a water inlet pipeline of the water tank and comprises a component A and a component B; according to the component A, when water flows,
water flow pushes impellers or rotors or Hall elements 4-8 to rotate, pulse signals or current and
voltage signals and the like are output through induction of the water flow, an intermediate
relay is pulled in, a circuit is on, and one or more groups of
electric heating tubes are electrified to work; when the water is turned off, the water stops flowing, the circuit is off, and the
electric heating tubes stops heating; according to the component B, a transverse through hole is formed in the small end of a
piston 4-9, a through hole is further formed in the middle of the
piston 4-9, in the water inlet process, water passes through the transverse through hole and enters the water tank via the hole in the middle of the
piston 4-9, entering of the water is not blocked in the water inlet process, when the water tank is full of water or the water inlet amount is larger than the water outlet amount and pressure in the water tank is increased, the large end of the piston 4-9 produces backpressure, the piston shifts, and a water inlet 4-11 is turned down or even turned off.