You could monitor when the Tank Level momentarily jumps using something similar to:
tagmax('cdt158','*-5m','*') - tagavg('cdt158','*-5m','*')
The above uses point 'cdt158' as the tank level and the time range of 5 minutes is just an example time frame.
Use the above for algorithm similar to if condition1 AND condition2 then "successful" else "failure" for the valuation of blowback.
Condition1 could be the test of the valve status. Condition2 could be the test for whether "tagmax('cdt158','*-5m','*') - tagavg('cdt158','*-5m','*')" is greater than some value.
Maybe the PE could be Event based on when the Tank Level gets an update.
Hope this helps.
This is great, I will test it out. Thank you for the help.