hard surface split rings 38 and 40 butt against opposing ends of sleeve 36 and the uppermost split ring 40 can make contact with shoulder 42 on the lower end of intermediate housing 22 to retain the upper housing 20 in place a limited amount of axial play between the upper housing 20 and the lower and intermediate portions 24 22 is permitted with shoulders 44 46 on the intermediate and upper housings 22 20 making contact when the weight of the drill string is applied as during drilling while split ring 40 butts up against shoulder 42 when the tool is under tension as during lifting out of the hole wear rings 48 50 and seal rings 52 54 are provided between the relatively movable assemblies described above and a suitable lubricant is provided on the relatively movable surfaces the neck 32 of the upper housing portion 20 has an elongated central bore 60 therein of constant diameter defining a passage for drilling fluid from the upper end of the tool downwardly toward the flow control means which will now be described seated in the central passage defined by the bottom housing 24 just downstream of the neck 32 and against a step 64 provided in the housing interior wall is a venturi assembly having a valve therein that provides intermittent interruption of the flow of drilling mud or fluid the drilling mud or fluid is pumped downwardly in well known fashion through the drill string from the surface and passes along the bore 60 in neck 32 in the direction of the arrows the manner in which this flow is intermittently interrupted or pulsed will be apparent from the following description the several views fig3 5.