I have a water pump(regular) with a bladder. The pumpcuts in and pumps up to the cut off pressure. Slowly, over approx an hour the pressure drops very slow (a little wiggling og the pressure gauge needle) and cut in at the starting pressure?
Turmed of the water supply to the house and same thing happens. New foot valve. Water comes from a closed cistern and about a 10 foot drop from pump.

OK! If you've shut the house supply off and the pressure still drops then one of two things are happening.
1. The new foot valve isn't doing its job, ( was the foot valve replaced because you were losing pressure and you thought that would fix the problem?) If so the foot valve is probably OK. Which means we open door #2.
2. There is a small leak in the suction line which shouldn't be too hard to check since it's only a 10 foot drop. Good luck, Tom

Hi Tom
Thanks

The drop (elevation difference)from the pump to the cistern is 10' but the total line is about 250 feet 4' underground. If I understand you correctly you are saying the potential leak is in the line(suuply) from the pump to the cistern. This would mean that the water is back flowing from the tank through the pump and leaking somewhere in the supply line?

Yep! That's what I figure. Was the foot valve replaced because you were losing pressure? If so the only thing left is the suction line. A band aid might be to install a check valve next to the pump on the suction side. That way you would retain house pressure. Good luck, Tom

Caper, that makes sense. With a 250 foot line, you have enough pipe to lose enough water to cause the pump to cut back on, and yet not lose prime. A CV near the pump is a good idea. Replacing the footvalve might not be too hard if you only have to pull 10' of pipe.