What is the most likely cause of meter creep in a retail liquid LPG meter that pumps against a closed valve?

Meter creep in a retail liquid LPG meter that is pumping against a closed valve is most commonly attributed to a leaky diaphragm in the differential pressure valve. When the valve is closed, there should be no flow, and the meter should not register any volume. However, if the diaphragm within the differential pressure valve is compromised, it may allow a small amount of liquid to pass through even when the valve is shut. This can cause the meter to register a flow even though the valve is closed, resulting in a phenomenon known as meter creep.

Each of the other options suggests different issues, but they do not align with the specific circumstances of meter creep under these conditions. For instance, an obstructed flow meter would typically affect the accuracy of flow measurement during operation rather than causing creep while at rest. A faulty pressure gauge could cause inaccurate pressure readings but would not directly impact the registration of flow when the meter is not actually measuring liquid movement. Similarly, an improperly calibrated meter would affect overall measurement accuracy but would not cause a continued registration during a closed-valve scenario without actual flow. Thus, the presence of a leaky diaphragm in the differential pressure valve is the most plausible explanation for the observed meter creep.