portion 26 accordingly the valve plug 20 is guided within chamber 18 while at the same time minimizing flow of fluid between portion 26 and the housing 14 this construction insures that the single plug check valve of the present invention may be used at all angle orientations the valve plug 20 further includes openings 28 in the first diameter portion which communicate with an internal passage 30 having a diameter d 4 for communicating fluid which passes through openings 24 in valve seat 12 through the valve body with particular references to fig1 4 the special design of the valve plug of the present invention which guarantees minimum pressure drop across the valve and thus maximum flow through the valve body will be described in order to insure minimum pressure drop across the valve and thus maximum flow through the valve it is a particular feature of the present invention that the first diameter portion 22 of the valve plug 20 define with the valve housing 14 an annular flow area a 2 in fig3 which is substantially at least as large as the flow area a 1 in fig4 defined by the valve seat 12 the annular flow area a 2 is equal to the area defined by the housing 14 minus the area of the first diameter portion 22 of.