wall 54 of constant diameter which extends toward a lower wall 56 of increasing diameter fig4 illustrates a third alternative embodiment where the cavity region 46 is formed by cap 44 having upper wall 52 of decreasing diameter extending from dirt trap opening entrance 50 toward middle wall 54 of constant diameter which extends toward a stepped increase in diameter forming lower wall 58 additionally valve body 12 may include a vane or ribs to direct particulates into dirt trap 18 port 20 includes a port opening entrance 22 a port wall 24 an undercut 26 and a land 28 see also fig1 b port opening 22 is adjacent to inlet passageway 15 port 20 has a decreasing diameter from port opening 22 toward undercut 26 in the preferred embodiment the cross sectional area of port 20 is circular and the diameter is greatest at port opening 22 and decreases continuously toward undercut 26 this decrease in diameter provides an angle between port wall 24 and longitudinal axis 40 of plug assembly 32 the goal is to maximize this angle this angle can be in the range of from about 15 to 45 degrees a more preferred embodiment having an angle of 30 degrees in the preferred embodiment the decrease in diameter is at a uniform rate however the decrease of port 20 diameter could be at varying rates undercut 26 is located adjacent to port wall 24 and is formed by a stepped decrease in diameter of port 20 this stepped decrease in diameter provides an angle between port wall 24 and the longitudinal.