Improvements in or relating to web driving apparatus

872,441. Feeding magnetic tapes. ELECTRIC & MUSICAL INDUSTRIES Ltd. March 14, 1958 [March 14, 1957], No. 8388/57. Class 40 (2). [Also in Groups XVI, XXIV and XXXIV] Magnetic tape driving apparatus comprises at least one reservoir capable of having suction applied thereto so as to create a partial vacuum in the reservoir to maintain a loop of tape therein, means for causing the degree of vacuum in the reservoir beneath the loop to vary in accordance with the position of the loop, and means whereby the feeding of tape to or withdrawal of tape from the reservoir is controlled in dependence on the degree of vacuum in the reservoir beneath the loop. As shown, the reservoir comprises a box 1, Fig. 1a, open at its upper end, the distance between the front and rear walls being only slightly greater than the width of magnetic tape 4 being fed. A loop of tape 4 closes the lower portion of the box. Slots 2 in the walls of the box are enclosed by a chamber 3 connected by a tube 5 to a source of suction. When suction is applied, the tape 4 is sucked in a downward direction. Should the bottom of the loop descend below the slots 2, the vacuum is decreased an amount corresponding to the vertical of the position of the loop. A tape reel 6, Fig. 2, is either driven or braked by a combined pneumatically operated clutch and brake mounted on a shaft 8. The clutch and brake comprises a pinion 9 axially movable on the shaft 8 in response to a differential in air pressure in chambers 15 and 17 defined by the pinion. A disc 12 carrying a ring 13 of friction material is secured to the shaft 8, while a pinion 10 having a ring 13 on its inner face is rotatable on the shaft 8. The pinion 10 is driven by a continuouslydriven pinion 11, the drive being transmitted to the reel 6 upon engagement of the frictional ring 13 on the pinion 9 with the ring 13 on the pinion 10. Similarly, the reel 6 is braked when a second ring 13 on the pinion 9 engages the ring 13 on disc 12. The position of the pinion 9 is determined by the vacuum within the box 3, Fig. 1a, in dependence of the length of loop therein. In an embodiment including a pair of reservoirs 21, 22, Fig. 3, tape 25 is unwound from one reel 26 and 27 and rewound on the other reel. The reels are each driven and braked by a combined pneumatically-operated clutch and brake 23 or 24 controlled as described above and provided with chambers D and B corresponding to the chambers 17 and 15, respectively. The tape is driven between the reservoir