Checking the zero of in line DP level transmitter while it is in line
A. Close the HP & LP and vent open the equalizer
B. Bypass the interlock if present. Close the LP side of the transmitter manifold. Open the equalizer valve of the transmitter manifold. Check zero
C. Close one valve and keep one side open (any of both sides HP or LP doesn’t matter) then open equalizer valve. TX should read zero.