Bilge pumps problems in transfering bilges & solutions

I think everyone will meet this issues. Sharing my experiences below,

1) Check your pump suction & discharge pressure
2) Close your suction valve. The suction pressure should drop down to vacuum. If the pressure gauge already shows vacuum, your pump inlet filter are already dirty.
3) Check that there is only 1 bilge well valves opened, it is harder to take suction if 2 are open
4) Prime your bilge well line/ pump with seawater properly, Fully open and slowly throttle close, closing observing the discharge pressure. once suction pressure shows slight vacuum, it means your pump is taking suction.
5) If fails, it could be your bilge well filters dirty. ( often this is not the cause )

I’ve experienced air leakage into the bilge system from the bilge well valves before, thus not able to take suction. (imagine sucking a straw with holes)
also i’ve experience small rags that got into the valve, choking the non return globe valve.

If all fails, problem can be your bilge pumps. Some pumps uses valves, these valves could be leaking, springs defective.