49. Open bypass valve and close the inlet and outlet valves for the back flushing filters.

A、
A、 Close bypass valve and open the valves for the back flushing filters.;

B、
B、 Open bypass valve and close the valves for the strainers.;

C、
C、 Close bypass valve and close the valves for the back flushing filters.;

D、
D、 Open bypass valve and close the valves for the back flushing filters.