the outer tube 32 relative to the inner tube 34 as described in greater detail below translation of the control knob 40 outer tube 32 relative to the shutter index element 44 inner tube 34 and the effect on fluid flow is shown in greater detail in fig5 8 in each of fig5 8 the control knob 40 fig4 a has not been shown for purposes of clarity instead only the support 56 which extends from the control knob 40 to the collar 38 fig4 a has been depicted further the shutter index element 44 is shown as including the axial slot 58 a connected to four circumferential slots 64 a 64 d as previously described the support 56 can be maneuvered along the axial slot 58 a into selective engagement with each of the circumferential slots 64 a 64 d thereby locating the support 56 within any one of the circumferential slots 64 a 64 d and resulting in a defined relationship of the outer tube 32 relative to the inner tube 34 to assist a user in positioning the support 56 the shutter index element 44 may further include indicia 66 a 66 d associated with the circumferential slots 64 a 64 d respectively the indicia 66 a 66 d may assume a wide variety of forms for providing a user with an indication of outer tube 32 inner tube 34 positioning for example the indicia 66 a may be.