inlet channel 171 b in the upper mounting plate 121 as well as fully encircling the small diameter o ring 181 v in similar fashion referring now to fig4 a and 4a 2 a small diameter o ring 182 v is positioned within the gap 160 encircling the outlet channel 172 b in the upper mounting plate 121 with a large diameter o ring 182 w positioned within the gap 160 and encircling both the outlet channel 172 a in the upper section 111 of the housing 110 and the outlet channel 172 b in the upper mounting plate 121 as well as encircling the small diameter o ring 182 v referring to fig4 a 4 a 1 4 a 2 4 a 3 5 a 5 a 1 the thickness or longitudinal y height of the large diameter o rings 181 w and 182 w is selected so that these o rings 181 w and 182 w are sealingly engaged within the gap 160 regardless of whether the mounting plates 120 are in the open or closed longitudinally y position so as to prevent fluid from flowing freely within the gap 160 the thickness or longitudinal y height of the smaller diameter o rings 181 v and 182 v is selected so that these o rings 181.