first chamber 136u and the third chamber 136l are in fluid communication it is understood that although the channel 148a is shown as disposed within the rotating shaft 12 it may be disposed with equal effect within the housing 10 a pressure relief arrangement 150 is provided for relieving the pressure in the third and the first chambers the arrangement includes a conduit or bore 152 provided within the floating piston 157 and communicating the second chamber 136c with the third chamber 136l it is likewise to be appreciated that the pressure relief arrangement may take any form whereby the third chamber and the first chamber may be relieved for example the channel 148a may be provided within the rotor 12 or the housing 10 in accordance with this invention the arrangement 150 includes a valve 158 provided in the conduit or bore 152 the valve element may take the form of a check valve having a ball 158a biased against a seat by a spring 160 the spring 160 exerts a force acting in the direction 162 urging the ball 158a toward the seat 174 to thereby interdict communication between the second and third chambers as will be seen herein the magnitude of the force imposed by the spring 160 is selected in accordance to a predetermined pressure magnitude which is desired to be present in the fluid within the first.