A method of integrity testing a filter capsule; said method comprising providing a manifold assembly unit comprising a filter capsule having a pressure input port, a feed port and a permeate port, a pair of valves in fluid communication with the feed port and a pair of valves in fluid communication with the permeate port, wherein each valve has an axial length and independently comprises a body having: a first end containing a face configured to be attached to an upstream component; a second end configured to be attached to a downstream component; and a bore extending axially from the first end to the second end ; a plunger axially movable within said bore between an open position and a closed position, the plunger having a first end and a second end; and an actuator (50, 50'; 80) operatively connected to the plunger by a pair of split rings , each split ring including a radially inwardly extending plunger engaging member and a radially outwardly extending actuator engaging member operatively connecting the actuator (50, 50'; 80) and the plunger , such that movement of the actuator (50, 50'; 80) causes the plunger to move axially between the open and closed positions without altering the axial length of the valve, wherein: the valve is in the closed position when the first end of the plunger is in alignment with the face of the body ; and the first end of the plunger being in alignment with the face of the body forms a steamable surface and a sterile barrier against the environment to a remainder of the interior of the bore , the plunger and a downstream component; said method further comprising: closing all but one of said valves; applying gas pressure to said pressure input port; determining the flow rate of said gas and comparing it to a predetermined value. a first end containing a face configured to be attached to an upstream component; a second end configured to be attached to a downstream component; and a bore extending axially from the first end to the second end ; a plunger axially movable within said bore between an open position and a closed position, the plunger having a first end and a second end; and an actuator (50, 50'; 80) operatively connected to the plunger by a pair of split rings , each split ring including a radially inwardly extending plunger engaging member and a radially outwardly extending actuator engaging member operatively connecting the actuator (50, 50'; 80) and the plunger , such that movement of the actuator (50, 50'; 80) causes the plunger to move axially between the open and closed positions without altering the axial length of the valve, the valve is in the closed position when the first end of the plunger is in alignment with the face of the body ; and the first end of the plunger being in alignment with the face of the body forms a steamable surface and a sterile barrier against the environment to a remainder of the interior of the bore , the plunger and a downstream component; said method further comprising: closing all but one of said valves; applying gas pressure to said pressure input port; determining the flow rate of said gas and comparing it to a predetermined value. closing all but one of said valves; applying gas pressure to said pressure input port; determining the flow rate of said gas and comparing it to a predetermined value. <EOS>