the flanged end of the compliant portion 74 the pocket 106 has a larger diameter than that of the needle 24 thereby to reduce the overall contact area between the compliant portion 74 and the needle 24 when the collar is slid along the needle 24 as described below the face of the compliant inner portion 74 has an integrally formed cylindrical boss 104 extending axially downward therefrom the boss 104 minimizes the contact area between the outlet and inlet assemblies 12 and 14 to provide a robust seal as will be explained below the compliant portion 74 preferably is made of ethylene propylene dimer monomer although other similar elastomers could be used that fits tightly around the needle 24 the collar 26 and compliant portion 74 move together along the length of the needle 24 the collar 26 is biased toward the lower end of the housing 22 toward a 34 closed 34 position by a spring 58 the spring 58 is compressed between the upper wall of the housing interior 48 and the collar flange 66 in the closed position the face 80 of the collar 26 that is the continuous surface defined by both the rigid portion 72 and compliant portion 74 is flush.