referring to fig1 through 4 , a prior art internal pulsation damper 10 for inclusion within a fuel rail for an internal combustion engine is formed as an elongate pillow 12 , fig1 showing a transverse cross - sectional view thereof . the shown cross - sectional shape is known in the art , and referred to herein , as a “ flat oval .” pillow 12 is provided with first and second diaphragm sides 14 separated and connected by longitudinal rigid short sides 16 of height 17 ( typically about 3 . 41 mm ) which are typically curved as shown such that the cross - sectional shape is a flat oval . sides 14 are joined at the ends of pillow 12 , as by compression of sides 14 ( pinching ) to form a crimp , defined by a flattened region 15 as shown in fig2 , and then welding 19 of sides 14 together as shown in fig2 and 3 , to form a sealed chamber 18 within pillow 12 . chamber 18 is filled with a gas , preferably air . pillow 12 is disposed within a fuel rail ( not shown in fig1 through 4 but similarly to improved damper 10 ′ disposed in a fuel rail 20 in an internal combustion engine 70 as shown in fig8 and discussed below ). the aspect ratio of pillow 12 , that is , the ratio of the typical height of sides 16 ( 4 . 8 mm ) to the typical width of sides 14 ( 17 . 2 mm ) is about 4 . 8 / 17 . 2 = 0 . 28 . in operation , pillow 12 is surrounded by fuel 22 being pumped from a source to fuel injectors ( not shown ) connected to the fuel rail . hydraulic pulses being transmitted through fuel 22 are absorbed by inward / outward flexure of diaphragm sides 14 and corresponding compression / expansion of gas in chamber 18 . the work done in flexing the sides and compressing the gas consumes the energy of a pulse . the damping characteristics of pillow 12 are limited , in part , by the volume of chamber 18 . a problem with a damper formed in accordance with the prior art is that the flat oval shape is compressed at each end by a press ( not shown ) to form the flattened region 15 . as short sides 16 are subjected to a progressively smaller radius , the long sides 14 are caused to freely flare outwards 21 until near and at region 15 the sidewall material collapses and is forced into a folded crease 23 along each side 16 . such creasing deforms and weakens the structure of the metal of the tube and predisposes the metal to fatigue failure along the crease . it is a primary object of the invention to prevent the formation of a fatigue - inducing crease at the extremities of sides 16 . referring to fig5 through 7 , an improved internal pulsation damper 10 ′ is formed in a fashion similar but not identical to prior art damper 10 . a portion of a first improved damper 10 ′ a is shown in fig5 along with a portion of a second improved damper 10 ′ b in preferred tooling in accordance with the invention as described below . the improvement consists in providing lateral constraint elements 30 for preventing sides 16 from freely flaring out in a first transverse direction 31 during compression of the tube in a second transverse direction 33 and thereby forming creases 23 as in the prior art . constraint elements 30 preferably comprises posts 32 spaced apart by essentially the long outer diameter of the raw tubing from which a damper is to be formed . posts 32 may be connected by a cross - member 34 to provide a rigid u - shaped structure resistant to flaring forces generated during compression of the tubing . preferably constraint elements 30 are rounded on the tube - bearing surface 36 to facilitate deformation of the tube into a crimp 37 without a sharp crease . preferably , a loose - fitting trough 38 having sides 40 and a bottom 42 is provided for holding the raw tubing of the damper during deformation of the ends thereof in accordance with the invention . in preferred tooling , posts 32 a and 32 b are spaced apart longitudinally of the dampers adjacent an anvil 44 having an anvil surface 46 of a length preferably greater than the combined length of compressed regions 15 a and 15 b such that a portion 15 x may be cut from the crimped material in a subsequent step ( not shown , as by conventional punching ) wherein adjacent pulse dampers are separated from each other . anvil 44 may be reciprocable 45 . such length extends the working life of a reciprocable 47 hammer 48 by requiring hammer 48 to have an equivalent length 50 greater than the length required simply to compress regions 15 a , 15 b . preferably , length 50 is selected to be less than the spacing of posts 32 a , 32 b such that a distortion zone 52 a , 52 b is created between the posts and the anvil / hammer , allowing the folding of the damper ends into a crimp 37 to proceed as follows without creating a crease 23 . as hammer 48 engages the raw tubing against anvil 44 , the tubing begins to flatten as in the prior art . being constrained from free flaring as in the prior art , however , by posts 32 , the tubing becomes flattened against the posts , forming shoulders 54 as the distance between walls 14 diminishes and creating a quasi - rectangular cross - sectional shape , as shown in fig7 . the thus - planarized sidewalls 16 then flare out abruptly between the posts and the anvil / hammer by bending about the posts through an angle 56 of preferably about 45 °. simultaneously , walls 14 progressively approach each other in a smooth deformation 58 , ultimately forming region 15 . thus , region 15 is formed as a transformation of the raw tubing “ flat oval ” profile without creating a longitudinal crease 23 . the folding is very similar to the “ gable end ” of a milk carton , as is well known in the prior art , except that the sidewalls flare radially outward to form region 15 as simply two thicknesses of material , rather than folding radially inward and then being tucked between walls 14 to form a complex region having both two and four thicknesses of material . in operation , lengths of raw metal tubing are provided having the proper diaphragm characteristics in walls 14 and support characteristics in walls 16 . the flat oval tubing has a short inner width 100 , a short outer width 102 , a long inner width 104 , and a long outer width 106 . such lengths may be , for example , about 20 feet and sufficient to form a plurality of dampers 10 ′. the tubing is inserted into trough 38 with a first end of the tubing extending between posts 32 a and across anvil surface 46 . hammer 48 is engaged , forming a first closed end preferably having an extended region 15 including a region 15 x . the hammer is retracted and the tubing is advanced along trough 38 past posts 32 a , 32 b by a distance equal to the desired length of a pulsation damper plus region 15 x . the hammer is again advanced to compress region 15 a , 15 x , 15 b , completing the closure of a first damper 10 ′ a and the initial closure of a second damper 10 ′ b . this sequence is repeated until the length of tubing is exhausted . as noted above , subsequently each region 15 x is chopped from the string of attached dampers 10 ′ to sever them and form a region 15 on the end of each , the regions 15 x being discarded or recycled . the damper ends are then hermetically sealed as by welding , soldering , or brazing , and preferably by welding 19 . referring to fig8 , improved damper 10 ′ may be suspended and secured in fuel rail 20 , for use in an internal combustion engine 70 , by capturing the pinched ends 15 of damper 10 ′ in mounts 60 disposed in the fuel rail , which may be attached to engine 70 as by brackets 72 . an internal fuel rail damper in accordance with the invention has a greatly extended working life when compared to a prior art damper . in an over - stress bench test , the improved damper was functional for more than 10 6 cycles , whereas the prior art damper failed in fewer than 10 3 cycles . while the invention has been described by reference to various specific embodiments , it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described . accordingly , it is intended that the invention not be limited to the described embodiments , but will have full scope defined by the language of the following claims .