NOVELTY - Hydrogen generator (1) comprises container (2) having aqueous solution of metal hydride; pump (5) connected to container, to pump out aqueous solution; reaction chamber (7) containing catalyst (10), connected with pump to receive aqueous solution; first liquid collecting area (30) connected with reactor chamber for collecting reaction exhaust products (31); gas outlet (13) connected to reaction chamber for extracting gaseous products; and controllable valve (37) connected to exhaust products outlet (32), and opening into environment.    USE - As hydrogen generators to supply fuel cells with gaseous hydrogen, e.g. for vehicles such as small aircrafts.    ADVANTAGE - The hydrogen generator has compact, lightweight structure. The controllable valve is rather high and the duty rate can be in the order of 1:10, where the path from outlet to conduit end is short and does not contain complex elements, thus preventing danger of crystallization. The controllable valve can block exit of liquid through discharging conduit, so as to discharge condensed water into fuel container or directly into pump. This can be suitable for cleaning cycle for restarting generator after interruption, thus preventing clogging of system by crystallization; or for diluting solution of metal hydride.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for operating hydrogen generator involving pumping quantity of aqueous solution from container into reaction chamber; awaiting initiation of catalytic reaction in reaction chamber; measuring pressure at pressure sensor (27) and temperature at temperature sensors (28); and adjusting temperature of reaction chamber by use of heating and cooling units.    DESCRIPTION OF DRAWING(S) - The figure shows sectional view of hydrogen generator.    Hydrogen generator (1)    Container (2)    Pump (5)    Reaction chamber (7)    Catalyst (10)    Gas outlet (13)    Pressure sensor (27)    Temperature sensors (28)    First liquid collecting area (30)    Exhaust products (31)    Exhaust products outlet (32)    Controllable valve (37)    Discharging conduit (46)