JimEli - sorry, you seem to have been ignored
2 questions for EC-135 experts:
If a main fuel tank transfer pump check valve failed, is it possible that the resultant rate of transfer into the supply tanks could be below the dual engine fuel burn rate?
At Max continuous power, possibly yes - although, with the line blocked there would still be a "Tx Pump" caption displayed to the pilot.
What would the consequence be if a pump with check valve was installed in a supply tank?
The pumps in the Supply Tanks are the prime pumps and are only on for the start until the engine driven pumps have sufficient "Suck". If the wrong pump had been installed and the check valve had stuck shut then the engine would not start. Once it is running, it would be difficult for the valve to close against the flow of fuel but, if it did so then the engine would stop.
Hope that is of some use.