small barbs 62 as shown in fig4 preferably needle body member 56 is made from 316 stainless steel or other suitable corrosion resistant material and the needle tip member 58 is made capable of providing a suitable sealing surface with radial seal 106 to be described below from corrosion resistant material such as pfte nylon polypropylene etc having good corrosion resistance and a low coefficient of friction the benefit derived from constructing the distribution needle from two different components is that the material of body member 56 is resistant to wear and corrosion thereby assuring accurate positioning of needle 18 and the material of needle tip member 58 minimizes friction between distribution needle 18 and sleeve 16 described below or other bearing surfaces such as between the tip portion of the distribution needle and the needle receiving inlet flow orifice 72 as described below this in turn enhances smooth accurate axial positioning of the distribution needle within the assembly the lowermost end 66 of the tip portion 68 of distribution needle 18 i e the lowermost end of the needle tip member 58 is conically shaped and the remainder of the tip portion is generally cylindrically shaped the distribution needle 18 has a series of ribs 70 extending circumferentially around approximately the upper two thirds of the tip portion 68 while approximately the lower one third of the tip portion 68 is smooth walled so as to fit through and slide easily within needle receiving inlet flow orifice 72 formed in the end wall 39 of the distribution sleeve 16 the number of ribs 70 may be between four and six and would depend on needle length the distribution needle 18 increases in diameter over the length of the frustroconical flow accelerating throat forming portion 74 to have essentially.