right angled cross in this closed position any pressure within the tank and particularly the force of liquid fuel will act on the web portions 52 to force the rims 55 closer together under most operating conditions the configurations and natural resiliency of these parts are sufficient to hold the check valve closed under some conditions however such as in cold weather when the elastomeric material tends to be stiff it is desirable to augment the closing force of the check valve parts for this purpose biasing means such as fieldable ring means in the form of an o ring or garter spring 60 see fig2 and 5 may be mounted on the check valve end of the body 30 in a groove 61 see fig4 and 6 in the outer surface of each of the finger like portions 42 this spring also augments the natural resiliency of the body 30 in biasing the web member rims 55 into sealing engagement with each other in use and referring particularly to fig3 the discharge end 15 of a fuel pump nozzle is inserted through the body 30 until it has forced the gusset members 50 apart and projected beyond the rim portions 55 this action of physically opening the check valve does not require excess stretching of any of its component portions since the total sum of the lengths of the rim surfaces 56 is substantially greater than the inner circumferential dimension of sealing lip 33 and therefore than the correspondingly outer circumference of the nozzle 15 rather the gusset members are simply spread apart as.