Altmann Analytik Check Valve Cartridge, Ceramic Ball & Seat, 2/pk, for Waters Modell 510, 515, 600, 610, 1515, 1525, 2690, 2690D, 2695, 2695D, 2795,

equivalent to Waters 700002399 The PerformancePlus™ Inlet Check Valve Cartridge is an optional check valve that helps with sticking issues.