Abstract: An apparatus includes a first pump module, a second pump module and a sealing disc. The first pump module includes a first flange having a first opening, a second flange having a second opening and at least one first pump. The second pump module includes a third flange having a third opening, a fourth flange having a fourth opening, and at least one second pump. The sealing disc is positioned between and in sealing contact with the second flange and the third flange and has a disc opening with a cross-sectional area that is less than a cross-sectional area of the second opening in the second flange and that is less than a cross-sectional area of the third opening in the third flange, where the disc opening is aligned with the first, second, third and fourth openings.