The forming valve must establish flow while the sheet is still within its useful forming range. A valve that opens late or moves slowly produces a pressure curve with a flat delay followed by an otherwise normal evacuation. This can resemble weak pump capacity or a cold sheet.
Measure the command and the pressure
The electrical command, pilot signal, valve position, and mold pressure should be compared on the same time base. A command that occurs on time but produces delayed pressure change indicates a mechanical, pneumatic, or flow problem at the valve. A late command indicates sequence logic, sensor, or controller timing.
Pilot pressure, solenoid exhaust, actuator seals, spool contamination, port size, and valve orientation should be checked. A valve selected for nominal pipe diameter may still have inadequate conductance for a rapid forming event. Replacement should be based on required flow and response, not connection size alone.