referring to the drawings , it will be seen that an illustrative embodiment of a roll assembly suitable for use in conjunction with the invention comprises an axle assembly 2 ( fig2 ) including a rigid tubular central or base axle member 4 and a first curved rigid tubular end axle member 6 having one end 8 fixed to a first end 10 of the central axle member . a second curved rigid tubular end axle member 12 may be fixed at one end 14 to a second end 16 of the central axle member 4 . referring to fig2 in which portions of end axle members 6 , 8 are shown , it will be seen that the end 8 of the first end axle member 6 is disposed within the central axle member 4 and that , in like manner , the end 14 of the second end axle member 12 is disposed within the central axle member 4 . thus , the outside diameter of the central axle member 4 exceeds the outside diameters of the end axle members 6 , 12 by twice the thickness of the central axle member tube wall . referring to fig1 in which a portion of one end axle member 6 is shown in detail , it will be seen that a first end support ring means 20 is disposed around the first end axle member 6 . a substantially identical second end sleeve means ( not shown ) is disposed around the second end axle member 12 . similarly , first intermediate support ring means 24 is disposed around the first end axle member 6 between the central axle member 4 and the first end support ring means 20 . in the embodiment illustrated , the first intermediate support ring means 24 comprises intermediate support ring 28 . the first intermediate support ring means 24 may include additional support rings , as shown in the above referred to related patent application , which is incorporated herein by reference . second intermediate support ring means 30 ( fig2 ) is disposed in similar fashion around the second end axle member 12 between the central axle member 4 and the second end support ring means . in the embodiment illustrated , the second intermediate support ring means 30 comprises intermediate support ring 34 . the second intermediate support ring means 30 may also include additional support rings , as shown in the above referred to related patent application . mounted on each of the support ring means 20 , 28 , 34 , the second end sleeve means , and the central axle member 4 , are spool means 50 comprising bearings 52 and rotatable spool shells 54 . each of the bearings 52 is supported by a support ring means or the central axle member 4 . roll surface means 58 , preferably a rubber - like sleeve , is mounted on the spool shells 54 and is rotatable therewith and is adapted to engage a web material , not shown herein , but shown in the above - mentioned related application . in fig1 it will be seen that moving means 60 are disposed within the end axle members 6 , 12 ( axle member 6 shown in fig1 ) and operate to automatically move the support ring means 20 , 24 , 30 relative to the end axle members to cause movement of the spool shells 54 , and thereby the roll surface means 58 , to automatically alter the pressure exerted on the web material by the roll surface means 58 . the moving means 60 for each of the support ring means are mounted on rigid bars 61 disposed in the end axle members and each comprises a piston and cylinder assembly 62 , including a cylinder 64 , a piston 66 disposed in the cylinder 64 , and a piston pin means 68 extending from the piston 66 through an opening 70 in the end axle member . a distal end 72 of the piston pin means 68 is connected to the support ring means 20 , 24 , 30 . in the embodiment illustrated in fig1 the end support ring means 20 , which is heavier than the intermediate support rings and which is not as well stabilized by the roll surface means , is connected to two of the piston and cylinder assemblies 62 . the intermediate support ring 28 is connected to a single piston and cylinder assembly 62 . each cylinder 64 in the end axle member 6 is provided with a first chamber 74 for a first fluid 76 acting on a first pressure surface 78 of the piston 66 and a second chamber 80 for a second fluid 82 acting on a second pressure surface 84 of the piston 66 . similarly , each cylinder 64 in the second end axle member 12 is provided with a first chamber 74 &# 39 ; for the first fluid 76 acting on a first pressure surface 78 &# 39 ; of the piston 66 and a second chamber 80 &# 39 ; for the second fluid 82 acting on a second pressure surface 84 &# 39 ; of the piston 66 , shown diagrammatically in fig2 . as may be seen in fig1 the chambers 74 , 80 are provided with diaphragm members 86 , such that the chambers are sealed except for fluid inlet and outlet means in each of the chambers . in like manner , diaphragm members are provided in the chambers 74 &# 39 ; and 80 &# 39 ;. all of the first chambers 74 , of which two are shown in fig2 for illustrative purposes , comprise part of a first circuit 88 containing the first fluid 76 , and each of the second chambers 80 comprise part of a second circuit 90 containing the second fluid 82 . similarly , all of the first chambers 74 &# 39 ;, one being shown in fig2 for illustrative purposes , comprise part of a third circuit 88 &# 39 ; containing the first fluid 76 , and each of the second chambers 80 &# 39 ; comprise part of a fourth circuit 90 &# 39 ; containing the second fluid 82 . the first fluid 76 and the second fluid 82 preferably are liquids , such as oil . in operation , the second fluid is maintained under substantially constant pressure . in each of the second and fourth fluid circuits 90 , 90 &# 39 ;, there is disposed a liquid / gas tank 91 ( fig2 ) in which a gas , such as air , from a respective gas circuit 92 , 92 &# 39 ;, is maintained under substantially constant pressure and acts upon a reservoir for the second fluid 82 . in each of the first and third fluid circuits 88 , 88 &# 39 ; there is disposed a master cylinder assembly 100 ( fig2 and 3 ) comprising a master piston 101 housed in a master cylinder 102 having a first master chamber 104 in communication with one of the first or third fluid circuits 88 , 88 &# 39 ; and adapted to contain the first fluid 76 for acting on a first master piston pressure surface 106 and a second master chamber 108 in communication with one of the gas circuits 92 , 92 &# 39 ;, and adapted to contain the gas for acting on a second master piston pressure surface 110 . each master cylinder assembly 100 is provided with a first rolling diaphragm 112 ( fig3 ) interconnecting the wall of the first master chamber 104 and the first master piston pressure surface 106 , and a second rolling diaphragm 114 interconnecting the wall of the second master chamber 108 and the second master piston pressure surface 110 . the master cylinder 102 is provided with a double tapered side wall 116 ( fig3 ). the tapers are structured such that as the master piston 101 moves , the effective area of one diaphragm is increased while the effective area of the other diaphragm is decreased . as the diaphragms move toward the center of the cylinder , more of the diaphragms is exposed to pressure and the diaphragms become pressure surface extensions of the pressure surfaces 106 , 110 . a substantially constant gas pressure exists in the second master chambers 108 and the second and fourth fluid circuits 90 , 90 &# 39 ;. the pressure in the first master chambers 104 and the first and third fluid circuits 88 , 88 &# 39 ; varies in response to a change in pressure between the roll and the web , which causes movement of the pistons 66 , which in turn causes movement of the master piston 101 . the changing first and third fluid circuit pressures create changing forces in the first and third fluid circuits 88 , 88 &# 39 ;, and the piston and cylinder assemblies &# 39 ; first chambers 74 , 74 &# 39 ; in the opposite direction of a changing force on the support ring means 20 , 24 , 30 . in operation , the above - described roll assembly operates to correct the problem of slack edges in a web of material by automatically adjusting its end profile to maintain a selected web tension . the piston and cylinder assemblies 62 are set by selection of pressure in the gas / liquid tanks 91 , and thereby the pressure in the second and fourth circuits 90 , 90 &# 39 ; such that the various forces acting upon the support ring means are balanced ; that is , the weight of the roll , the tension on the web , and the like , are in equilibrium . as a rolling operation progresses , the above - described roll assembly operates to correct the problem of slack or overly - tensioned edges in a web of material by automatically adjusting its end profile to maintain a selected web tension . for example , the web running over the ends of the roll may be slack for lack of proper contact with the roll &# 39 ; s ends . if web tension at an end of the roll is less than that for which the system is set first fluid 76 pressure urges a spool 54 ( fig1 ), and thereby the roll surface means 58 , downwardly into the web . as first fluid 76 leaves the master cylinder chamber 104 , through the circuit 88 , to enter the first chambers 74 of the piston and cylinder assemblies 62 , the master cylinder tapered walls 116 cause the first fluid pressure to increase in the circuit 88 to create greater force in the chambers 74 , to maintain the spool 54 in its adjusted position until there is a change in rolling conditions . as the spool 54 moves downwardly to urge the roll surface means 58 into more forceful contact with the web , pressure in the chambers 74 is required to overcome the tendency of the roll surface means 58 to return to its original position . the master cylinder operates , through the fluid circuits 88 , 88 &# 39 ;, to maintain pressure in the chambers 74 , 74 &# 39 ; sufficient to overcome slack conditions as they occur , and also to balance the spring bias of the surface means 58 toward its &# 34 ; neutral &# 34 ; position . it is to be understood that the present invention is by no means limited to the particular construction herein disclosed and / or shown in the drawings , but also comprises any modifications or equivalents within the scope of the disclosure .