can also be optimized for the expected flow velocities there can be ridge combinations that are transverse as shown in fig4 combined with some ridges that are closer to parallel to the flow direction a surface roughening on the face of the insert that faces the passage 44 is another alternative to control the vortex 32 u2032 another approach is seen in fig5 where the insert 65 has a void 66 that in the fig5 is illustrated as square here again as in fig3 and 4 what is shown is a part of the insert 64 without the mirror image of it that is not in the illustration here again the void shape can be varied and optimized by mathematical modeling there are other options for vortex control that can be implemented for one the width of the gap 36 can be varied another approach is to increase the volume of the space behind the flapper and the surrounding housing one example is to machine grooves on the back side of the flapper that faces the wall 42 u2032 such as schematically illustrated by the dashed line 68 there is a limit to the extent that the grooves on the back of the flapper can be used especially in the larger sizes as the flapper has to take large pressure differentials when closed and adding grooves can promote flapper distortion.