Next, touch two test points downstream of the valve (points C and D) and compare intensity levels. If the sound is louder when comparing the first downstream (C) with the second upstream test point (B), the fluid might well be is passing through. If the compared downstream sound level is low, the valve is closed. If the second downstream test point (D) is louder than the first downstream test point (C), this indicates the sound is transferred from a source further downstream and indicates the valve may not be leaking.