Pressure drops when water pump shuts off

[aib]

I have a bladder water tank and above-ground water pump, with 30/50 psi range. I open a tap to drain water but close it as soon as I hear the pump starting at about 30 psi. The pressure gauge on the pump goes close to 50 psi, but as soon as the pump shuts off the pressure drops rapidly to about 40 psi, and then slowly to about 38 psi. I left it overnight and it still showed 38 psi the next morning. Is this a check valve problem?

 

[Reach4]

Are the pressure gauge and pressure switch very close to the bladder tank and connected by a big pipe?

 

[Sponsor]

 

[aib]

I've inserted a picture showing the gauge, and the pressure switch in the blue box on the side of the pump. Connection to the tank is with 7/8 inch pipe, total length about 40 inches.

 

[Valveman]

It could be a bad pressure tank as that kind is not known for lasting very long.