than having excess unvaporized liquid coolant being entrained in the impinging hot gas stream and being convected downstream where it would have no or minimum cooling benefit to the strut an example of the circumferential variation in coolant passage is illustrated in fig7 the housing 30 is provided with a passageway 47 therethrough which communicates with the conduit 45 on the one hand and with a conduit 49 on the other hand communicating with a reservoir 51 of cooling fluid via a valve 53 and a pump 55 as should be understood the valve 53 may be selectively opened and closed and the pump 55 may be selectively activated and deactivated to control flow of cooling fluid from the reservoir 51 through the conduit 49 passage 47 conduit 45 passage 43 chamber 39 and thence out the orifices 41 with further reference to fig6 it is seen that passageways 57 and 59 communicate on the one hand with the interior of the cylinder 31 and on the other hand with respective conduits 61 and 63 a four port reversing valve 65 is interposed between the conduits 61 and 63 an further conduits 67 and 69 the conduit 67 is connected to the outlet 71 of a sump 70 via a valve 73 and a pump 75 the conduit 69 directly connects with an inlet 79 of the sump 70 as should be understood with.