double check

Question 1

1st check valve pressure drop less than 1 psid

Answer 1

debris fouling check seat

debris fouling second check seat with back pressure

inlet pressure variation causing inaccurate gage reading

damaged seat or seat disc

worn guide bushing or stem

Question 2

second check fails to hold backpressure during the field test. or fails to hold 1 psid during duration of flow testing

Answer 2

outlet gate valve not closed completely

debris fouling second check

disc not moving freely

damaged seat or seat disc

worn guide, bushings or stem