from reservoir 16 through pipe 18 through passage 94 through port 96 around armature 44 through port 54 and into the gas storage device 66 through port 64 around armature 46 through port 42 through passage 104 and through pipe 22 to tube 10 after this predetermined time has expired solenoids 40 and 42 are deenergized enabling the gas stored in gas retaining device 66 to be retained in the event this amount of gas is insufficient to restore the gas pressure in laser tube 10 to the proper level as sensed by the voltage detector 30 the voltage detector 30 will again send the appropriate pressure related signal through line 32 to the voltage comparator 31 to reinitiate the same cycle and which cycle is repeated until an adequate pressure is reestablished in laser tube 10 thus signifying an adequate volume of gas within laser tube 10 in the second embodiment schematically illustrated in fig3 an alternative gas metering device 20 39 replaces the previously described gas metering device 20 of fig1 and 2 and the timer 34 39 replaces the previously described timer 34 otherwise those parts which appear in both fig1 and 3 are given the same numerical references and the further description will primarily refer to the alternative gas metering device 20 39 shown in fig4 in fig4 the single solenoid 110 includes an armature 112 having a valve closure block 114 which serves to open and close the port 116 and is loaded by a spring 118 which bears against a spring loading block 120 forming port 122 connected to passage 124 in block 126 held by c ring 128 a.