to be described and are also equipped with observation ports 52 54 a bracket 56 58 is secured to the outer surface of each sidewall 30 32 and supports a spherical mount 60 62 the deflector 14 is made up of two largely mirror image half frustoconical walls 64 66 with each wall being secured to and extending along the length of a corresponding housing half 22 24 so that when the halves 22 and 24 are closed together the walls 64 66 cooperatively define the substantially frustoconical deflector 14 as illustrated in fig4 and 5 the wall 64 is welded or otherwise affixed to the inner surface of sidewall 30 and is further supported by means of tabs 68 secured to rear end wall 26 as such it will be observed that a semicircular generally triangular in cross section open ended airway 70 is defined between the outer surface of wall 64 the inner surface of sidewall 30 and the inner surface of end wall 26 a semicircular air outlet 72 is in communication with airway 70 and is defined between the inboard margin 74 of wall 64 and a semicircular collar 76 the latter being secured to and extending forwardly from rear end wall 26 the frustoconical wall 66 is likewise secured to the inner surface of housing sidewall 32 thereby also defining a semicircular generally triangular in cross section airway 78 between the outer surface of wall 66 the inner surface of sidewall 32 and the inner surface of end wall 28 a lower.