Valves can be identified by the valve numbers that are on the wires going to them. See this article for view of the valves,
PPC4, PPC3, PPC2+, PPC2-AF - Valve inspection
If you have a leak it is most often the VENT valve (5) or a down valve (3 or 4) that are leaking.
Q-RPT module valves are not shown but are as follows:
Valve 7 - Low Q-RPT vent valve (protects low Q-RPT is valve 8 leaks)
Valve 8 - Low Q-RPT isolation valve (closed when hi Q-RPT is being used)
Valve 9 - TEST(-) vent valve. In normal operation with BG or G Q-RPTs, this valve is
closed during fine pressure control.
PPC3 Manual can be viewed or downloaded here,