In a tubular filter-aid filter, when the filter starts to clog and requires backwashing, inlet and outlet valves are __ and the drain valve is __.
A. Open, open
B. Open, closed
C. Closed, closed
D. Closed, open
Answer: D
In a tubular filter-aid filter, when the filter starts to clog and requires backwashing, inlet and outlet valves are __ and the drain valve is __.
A. Open, open
B. Open, closed
C. Closed, closed
D. Closed, open