Not sure where you got the area in shear of a 10-32 screw.... but it looks like you took the diameter of the head, and ignored the hex hole for the Allen key.... I use an area of 0.047 sq.in. for the head of a 10-32 screw.... Otherwise your math looks fine.... High tensile SHCSs are usually rated at 170 Ksi for tensile, which would be 102 Ksi in shear.... So, I would use (170,000 x 0.60) = 102,000 x 0.047 = 4794 lbf. / 3 = 1598 lbf. x 4 screws = 6392 lbf.... Since your required load is 2167 lbf. and you already allowed for the 3:1 safety margin, you should be more than OK.... PROVIDING that the pockets in the valve are deep enough that the shear line is actually going through the head of the screw....If, on the other hand, the shear line is through the threads, the area is only 0.020 sq.in.... This would give 102,000 x 0.020 = 2040 lbf. per screw.... For 4 screws, that is 8160 lbf., divided by the load of 2167 lbf. gives a safety margin of 3.7:1, which should still be OK.... If the screws you are using are only 145 Ksi tensile strength, then you would be a bit less (but still just over 3:1) with the threads in shear.... Bob
The forces applied to a valve like this will be axial, putting the screws in sheer tension. The amount of space between fasteners side to side is not overly important since the load will be applied front to back. What do you mean yield during testing was concerning? Did you manage to get holes in 4130 tubing to elongate?
maybe Bob can do the math on the single Pin dowel method.. I know its strong enough to deform most tubes before failure, So ive never had any trepidation using it ( i only do it with 1/4 inch dowels ) This assumes the pin is 4140 or 4130