Fig. 3 Nylon Iockwheels fit into slots in base; a quarter turn of locking ring then seals funnel to base.
7 Connect the filtering flask or manifold to the vacuum source, with silicone rubber tubing, pour the
sample into the funnel and apply vacuum to filter the sample.
CAUTION
If the vacuum source is a dry–air pump, such as Millipore Cat. No.
XX55 000 00, liquids should not be allowed to enter the pump intake. The
simplest way to guard against this is to install a second side-arm flask
between filtering flask (or manifold) and the pump as shown in Figure 4.
Fig. 4 Second side-arm flask connected in series keeps liquid droplets or water vapor out of pump.
8 When the sample level has lowered to the neck of the funnel, rinse down the funnel walls with about
30 ml of filtered water or appropriate solvent, not letting this liquid strike the filter surface. This flushes
residue from the walls, and helps to secure a uniform contaminant distribution on the filter surface for
statistical counting. In microbiological tests, the rinse fluid must be sterile and buffered. In other tests,
a filtered jet from the Millipore Solvent Filtering Dispenser can be used.
9 As soon as all sample and flushing fluid has passed through the filter, shutoff the vacuum and gently
rock the holder assembly to break the stopper seal and vent the flask vacuum. Rotate the locking ring
to the left until it stops, releasing the funnel from the base. Lift off the funnel and transfer the filter with
smooth–tip forceps to a clean petri dish for visual particle counting, or to a prepared media pad or agar
4
