Tightened the (as found closed) 10" gate valve at CP4 and then vented the non-CP4 side.  There may have been a slight improvement in CP4's pressure as the result of this exercise (see attached graph).  I was working alone and wasn't able to observe the peak pressure on the connected pump cart when the unpumped "dead volume" of the gate valve was valved-in to the pump cart but I could tell that the gas load was enough to slow the pump cart's turbo.  

Tomorrow I will remove the 10" gate valve's zero-length reducer and install the turbo, gauge, valves and RGA components needed for the decommissioning of CP4 later in February.