In steady state or normal operation, both locks remain open and the by-pass or equalizer remains closed. In this way, it is ensured that you are perfectly measuring the pressure difference between the HP side (high pressure) and the LP side (low pressure).
In case you need to check the “0” of the instrument, simply open the by-pass and close the HP lock, thus equalizing the pressure on both sides and checking the “0” of the instrument.
To install an instrument (with the manifold mounted and connected), the manifold must be mounted and the by-pass and HP lock open slowly. In this way, the pressure is established in both chambers of the instrument, simultaneously, avoiding damaging it. Then the LP lock should be opened and the by-pass slowly closed, thus establishing the Δp between the branches.
