shell 30 and flows into the mounting recess 561 of the support lid 56 through the o ring 443 of the push rod 44 and the bottom edge of the support lid 56 when the water is gradually filled with the mounting recess 561 the water also flows in the through hole 444 of the push rod 44 through the aperture 445 of the push rod 44 when the water pressures in the through hole 444 of the push rod 44 the mounting recess 561 of the support lid 56 and the receiving recess 32 of the inner shell 30 are the same the pressures differences are eliminated and the elastomer 41 pushes the push rod 44 reposition during a certain time when the push rod 44 is pushed to original position the o ring 443 of the push rod 44 seals the through hole 33 of the inner shell 30 so that the water cannot flow out of the inner shell 30 therefore the water stops flowing meanwhile the water is filled with the receiving recess 32 of the inner shell 30 and between the through hole 444 of the push rod 44 and the mounting recess 561 of the support lid 56 to allow the water to flow again the push rod 44 is pushed into the inner shell 30 again the water filled between the through hole 444 of the push rod 44 and the mounting recess 561 of the support lid 56 forces the annular wing 431 of the gasket 43 to retract toward the push rod 45 then the water can flow into the receiving.