Abstract: A sprinkler head assembly rotatable about a generally vertically extending axis, an impulse arm operable in response to the flow of water under pressure for effecting progressive movements of the sprinkler body about said axis, an outwardly facing annular valve seat on the sprinkler body disposed in surrounding relation to the outlet, a poppet valve cooperable with the annular valve seat, a mounting assembly for mounting the poppet valve on the sprinkler body for movement exteriorly of the sprinkler body (1) from an open position disposed out of the path of the stream progressively through the stream and generally inwardly onto the outwardly facing annular valve seat into a closed position with respect to the outlet so as to contain water under pressure within the sprinkler body and prevent flow thereof outwardly of the outlet beyond the annular valve seat and (2) from the closed position generally outwardly from the outwardly facing valve seat and progressively out of the stream into the open position, and a