cycle may last about 4 to 5 minutes under maximum water demand full load engine conditions the discharge being produced by the spring 102 as modified by manifold suction pressure when the chamber 84 is discharged the brief liquid refill cycle takes place on shutting down the engine the ignition circuit is opened and hence the energization of all circuits is terminated this then open circuits the solenoid valve 26 which permits the discharge of water from the vacuum pump 24 by way of line 47 valve 26 and line 45 back to the reservoir 32 under the action of the spring 102 referring to fig4 the spray nozzle means 50 is illustrated as being connected by bifurcated connections 110 with spacer plate 40 having siamesed bores 112 112 therethrough for a twin barrel carburettor 36 in the case of fuel injected vehicles either port injected or throttle body fuel injected the water inlet is located below downstream of the butterfly throttles such that the water injection rate is influenced by the butterfly air control or the air fuel control respectively in operation of the liquid injection cycle when the force generated by water entering inlet 54 as modified by vacuum from the induction manifold 38 exceeds a predetermined.