46 of housing 44 u2032 return to the intake 46 is through the hollow shaft 14 and along the outside of the shaft 14 through the ball bearings 16 into the chamber 76 which connects through the hole 78 formed near the base of the blades 80 comprising impeller 18 e g in the lower pressure portion of the volute referring to fig2 a second alternative embodiment of the pump of the present invention is indicated generally at reference numeral 182 in this second embodiment all the component parts thereof are similar to those of the embodiment shown in fig1 and are numbered with the same reference numeral preceded with a u201c 1 u201d e g impeller 18 in fig1 corresponds generally to impeller 118 in fig2 pump 182 is particularly intended for use with those fluids such as liquid nitrogen which can be vented to the atmosphere and circulates the fluid being pumped internally in the same manner as does pump 10 in fig1 but also provides a check valve 184 through which a portion of the pumped fluid is passed to the atmosphere through a vent tube 185 from the back half 144 u2033 of housing 144 where the pumped fluid is known to be free of water moisture and other materials that might freeze at the low temperature of the fluid to being pumped the vented fluid can also alternatively be captured.