referring now to the drawings , and particularly to fig1 the invented combined clutch and brake apparatus 100 includes a brake thrust disk 3 with ventilation holes 71 , a pressure disk 5 with ventilation holes 72 , a clutch thrust ring 11 , and a pneumatic cylinder 6 kinematically connected to a hub 1 . the hub 1 is non - rotatably mounted on a shaft ( not shown ) that is driven intermittently by the clutch . the brake thrust disk 3 is mounted on a first end 66 of the hub 1 . the brake thrust disk 3 is secured to the hub 1 by first hub screws 2a . the pneumatic cylinder 6 is mounted on a second end 67 of the hub 1 opposite the brake thrust disk 3 . the pressure disk 5 is positioned between the brake thrust disk 3 and the pneumatic cylinder 6 and mounted in a central region 68 of the hub 1 . the pressure disk 5 is movable along splines 4 on an outer surface 69 of the hub 1 . the pneumatic cylinder 6 includes a casing 7 which is movable along splines 4 on the outer surface 69 of the hub 1 . the casing 7 has an annular cavity 30 opening in a direction opposite the pressure disk 5 and having ventilation holes 31 symmetrically spaced in a base 25 of the casing 7 . the ventilation holes 31 provide cooling air to the friction zone of the invented combined clutch and brake apparatus 100 . a movable piston 8 is movably mounted in the annular cavity 30 . the movable piston 8 is sealed in the annular cavity 30 at the base 25 of the casing 7 by a second sealing collar 10 and at a distal end 28 of the casing 7 by first sealing collar 9 . the piston 8 forms an exterior face of the invented combined clutch and brake apparatus 100 . between the movable piston 8 and the casing 7 is an internal space . the hub 1 has openings 47 through which compressed air passes into channels 48 in the base 25 of the casing 7 . the compressed air is then fed into the internal space 49 of the pneumatic cylinder 6 . feeding compressed air into the pneumatic cylinder 6 actuates the movable piston 8 . the casing 7 of the pneumatic cylinder 6 is positioned on the hub 1 such that the body can move axially along the splines 4 . the pneumatic cylinder 6 can therefore change its position relative to the hub 1 . a thrust disk 20 is used to secure the casing 7 of the pneumatic cylinder 6 to the second end 67 of the hub 1 . the thrust disk 20 is secured to the hub 1 by second hub screws 2b . referring now to fig3 and 5 , the thrust disk 20 has an outer ring of holes symmetrically spaced which alternate between a thrust disk smooth openings 21 and a thrust disk threaded openings 22 . as shown in fig5 first thrust ring bolts 23 are inserted through the smooth openings 21 . spring washers 24 are positioned between the heads of the first thrust ring bolts 23 and the thrust disk 20 . the first thrust ring bolts 23 extend into an external surface 29 of the casing 7 of the pneumatic cylinder 6 . as shown in fig4 second thrust ring bolts 26 are inserted through the threaded openings 22 . gage adjustment washers 27 are positioned between the heads of the second thrust ring bolts 26 and the thrust disk 20 . the second thrust ring bolts 26 abut the external surface 29 of the casing 7 of the pneumatic cylinder 6 . referring again to fig1 a clutch thrust ring 11 is attached to an internal surface 19 of the casing 7 of the pneumatic cylinder 6 . a clutch friction ring 14 is positioned between the clutch thrust ring 11 and the pressure disk 5 . a brake friction ring 12 is positioned adjacent the clutch friction ring 14 between the pressure disk 5 and the brake thrust disk 3 . first pins ( not shown ) are placed through holes 60 in a distal region 61 of the brake friction ring 12 and are attached to the frame ( not shown ) of the machine in which the invented combined clutch and brake apparatus 100 operates . the first pins allow the ring 12 to move axially and prevent the ring 12 from moving radially . second pins ( not shown ) are also placed through holes 62 in a distal region 63 of the clutch friction ring 14 and are attached to the rotatable or accelerating parts . the second pins also allow the ring 14 to move axially and prevent the ring 14 from moving radially . first brake friction elements 13a are positioned on a proximal region 64 of the brake friction ring 12 adjacent to the brake thrust disk 3 . second brake friction elements 13b are positioned on the proximal region of the brake friction ring 12 adjacent to the pressure disk 5 . first clutch friction elements 15a are positioned on a proximal region 65 of the clutch friction ring 14 adjacent to the pressure disk 5 . second friction element 15b are positioned on the proximal region of the clutch friction ring 14 adjacent to and the clutch thrust ring 11 . the pressure disk 5 includes cups 17 spaced apart and positioned in a region 54 intermediate the central and outer portions of the pressure disk 5 below the friction elements 13 , 15 . the cups 17 have a closed end 18 and open toward the pneumatic cylinder 6 . braking springs 16 are positioned in the cups 17 . each braking spring 16 is supported at a first end 58 by the closed end 18 of the cup 17 . a second end 59 of each braking spring 16 engages recesses 70 in the internal surface 19 of the casing 7 of the pneumatic cylinder 6 . during operation , the friction elements 13 and 15 become worn and the stroke of the piston 8 must be adjusted accordingly . the adjustment is accomplished by use of bolts 32 installed through the pressure disk 5 and into the pneumatic cylinder 6 . preferably , each of three bolts 32 are inserted through one of three holes 52 symmetrically spaced in a base 53 of the pressure disk 5 . the holes 52 allow the head of the bolts 32 to be positioned completely within the width of the pressure disk 5 . the bolts 32 pass through the ventilation holes 31 , through holes 35 in the base 25 of the casing 7 , and through a proximal region 55 of the piston 8 . gage adjustment washers 34 are positioned on the bolts 32 in a gap between the base 25 of the casing 7 and the piston 8 . the bolts 32 are secured by check - nuts 36 positioned on the piston 8 opposite the gage adjustment washers 34 . each bolt 32 is surrounded by a gage sleeve 33 which extends from the head of the bolt 32 to the gage adjustment washers 34 . the wearing of the friction elements 13 and 15 creates clearances between the friction elements 13 and 15 and their corresponding surfaces . a means is therefore provided for the stepless adjustment of the disks to eliminate the clearances and to keep the friction elements 13 and 15 in contact with their corresponding surfaces . the unit for stepless adjustment of clearances between the frictional disks 12 and 14 , and also between the disks 5 and 11 , includes an adjustment nut 37 with stiffening ribs 38 on its circumference 57 . the nut 37 is installed on the distal end 51 at the external side 50 of the brake thrust disk 3 , and the device for locking the adjustment nut 37 to prevent it from turning around the axis is made , for example , as two t - shaped stops 39 . the stops 39 are installed diametrically opposite to each other on the external side surface 56 of the nut 37 . the vertical cylindrical part 40 of the stop is installed in a radial opening 41 made in the adjustment nut 37 . the specially made lower end 42 of the stop 39 interacts with the same profile surfaces of one of the symmetrical grooves 43 located in a circular pattern on the external side surface 50 of the thrust disk 3 of the brake . the horizontal part 44 of the t - shaped stop 39 is rigidly attached by means of bolts 45 to a platform 46 made on the external side surface 56 of the adjustment nut 37 . in operation , the invented combined clutch and brake apparatus 100 works as follows . after a signal , compressed air is fed through the openings 47 in the hub 1 , through the channels 48 in the base 25 of the pneumatic cylinder casing 7 and into the cylinder internal space 49 between the cylinder casing 7 and the movable piston 8 . the compressed air causes the piston 8 to move axially away from the casing 7 . as the piston 8 moves away from the casing 7 , the bolts 32 , gage sleeves 33 , the washers 34 , and the check - nuts 36 connecting the pneumatic cylinder 6 and the pressure disk 5 force the pressure disk 5 toward the clutch thrust ring 11 . as a consequence , braking spring 16 is compressed between the casing 7 and the pressure disk 5 . at the same time , the pressure disk 5 moves axially away from the second brake friction elements 13b on the brake friction ring 12 thereby releasing the brake . as the pressure disk 5 continues moving axially toward the casing 7 , the pressure disk 5 presses against the first clutch friction elements 15a on the clutch friction ring 14 causing the second clutch friction elements 15b to press against clutch thrust ring 11 thereby engaging the clutch . as compressed air is released from the internal space between the casing 7 and the movable piston 8 , the braking springs 16 force the pressure disk 5 axially away from the casing 7 . consequently , the pressure disk 5 releases the second clutch friction elements 15b on the clutch friction ring 14 from engagement with the clutch thrust ring 11 thereby releasing the clutch . furthermore , the braking springs 16 force the pressure disk 5 axially toward the brake thrust disk 3 causing the first brake friction elements 13a to press against the brake thrust disk 3 thereby engaging the brake to slow down the driven parts of the invented combined clutch and brake apparatus 100 and to end their rotation . because friction elements 13 and 15 wear out during operation of the invented combined clutch and brake apparatus 100 , stepless adjustments must be made to the clearances between the brake friction ring 12 and the brake thrust disk 3 and between the clutch friction ring 14 and the clutch thrust ring 11 . the present invention allows the stepless adjustments to be made from either the clutch end or the brake end or simultaneously from both ends of the engagement unit . from the brake end , the clearances between the brake thrust disk 3 and the brake friction ring 12 can be adjusted as follows . first , the bolts 45 are unscrewed and the diametrically opposed t - shaped stops 39 are removed from the radial openings 41 . the lower ends 42 of the t - shaped stops 39 are removed from one of the grooves 43 . next , the adjustment nut 37 is rotated as far as required to adjust the clearances between the brake thrust disk 3 and the brake friction ring 12 . the t - shaped stops 39 are reinstalled in the external side surface 56 of the adjustment nut 37 and positioned in the radial openings 41 such that the lower ends 42 of the stops 39 enter one of the grooves 43 . the bolts 45 are then screwed into place . from the clutch end , the clearances between the clutch thrust ring 11 and the brake friction ring 14 can be adjusted as follows . first , the three first thrust ring bolts 23 are loosened and the three second thrust ring bolts 26 are unscrewed from the threaded openings 22 . next , gage adjustment washers 27 are removed from between the heads of the bolts 26 and the thrust ring 20 . the three second thrust ring bolts 26 are then screwed into the threaded openings 22 until their free ends abut the external surface 29 of the casing 7 of the pneumatic cylinder 6 . when a set of gage adjustment washers 27 are removed , the bolts 23 and 26 move the casing 7 closer to the pressure disk 5 at a distance equal to the thickness of the washers 27 removed from the bolts 26 . as a result , the distance between the pressure disk 5 and the clutch thrust ring 11 is reduced and the clearances between the first clutch friction elements 15a and the pressure disk 5 and the clearances between the second clutch friction elements 15b and the clutch thrust ring 11 and disks are adjusted . often it is necessary to adjust the axial travel of the piston 8 in the annular cavity 30 of the casing 7 of the pneumatic cylinder 6 . the present invention allows the axial travel of the piston 8 to be adjusted by removing the check - nuts 36 from the bolts 32 . adjustment washers 34 can then be removed or added as necessary . the check - nuts 36 are then replaced on the bolts 32 . removing adjustment washer 34 reduces the distance between the piston 8 and the pressure disk 5 thereby decreasing the length the piston 8 can travel axially away from the pressure disk 5 . from the foregoing , it is readily apparent that we have invented an improved combined clutch and brake apparatus having increased reliability and safety and an increased service life . by providing a pneumatic cylinder having a movable piston positioned in an annular cavity in the casing of the cylinder where the movable piston forms an exterior face of the invented combined clutch and brake apparatus , the present invention allows easy access to perform a fast replacement of worn out sealing collars in the pneumatic cylinder . the present invention also provides a means for simple time - saving stepless adjustment of clearances between the friction elements and the clutch and brake disks caused by wear to the friction elements . similarly , the distance that the movable piston will travel can be efficiently adjusted as desired . further , the present invention allows a failed sealing collar to be replaced efficiently . as a consequence , the present invention allows the clearances between the friction elements and the clutch and brake disks and the distance that the movable piston will travel to be serviced in less than 3 minutes . the present invention is an apparatus than operates more economically than heretofore has been possible . it is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof , and that various modifications and additions may be made to the apparatus by those skilled in the art , without departing from the spirit and scope of this invention , which is therefore understood to be limited only by the scope of the appended claims .