other side of valve 5 as well as to the normally open port of a manually operated three way valve 8 via an accurately adjustable metering valve 10 providing a passage of variable diameter valve 8 may be a ball valve air regulator 3 is also connected to deliver driving air to air driven hydraulic fluid pump 20 the common port of three way valve 8 is connected to the operators 21 39 and 22 39 of air operated hydraulic fluid control valves 21 and 22 valve 21 is normally closed while valve 22 is normally open these being the states which they assume when the air pressure in their operators drops below a particular value all of the remotely controlled valves illustrated in the figure are shown in their normal state the form in which the valves are illustrated is selected to permit easy understanding of their operation and is not intended to suggest any specific form of construction thus each valve in the system can be a slide valve ball valve flap valve etc pump 20 has its inlet side connected to the supply outlet of a hydraulic fluid reservoir 19 and its outlet side connected to one side of valve 21 the other side of valve 21 is in turn connected to one side of valve 22 while the other side of the latter valve is connected to a line for returning hydraulic fluid to reservoir 19 the conduit connected between valves 21 and 22 is also connected to a manually operated shut off valve 23 whose other side is connected to a series arrangement of a manually operated valve 25 and a relief valve 27 leading to the return line to reservoir.