LAARS Mighty Max HH (Sizes 320M - 1000M) - Installation, Operation and Maintenance Instructions - Manual (Page 21)

Mighty Max Hydronic Boiler Page 21
The difference in pressure between the venturi
inlet tap and the gas plenum tap (see Figure 16). This
measurement is taken by connecting the positive side
of the manometer to the venturi inlet tap and
connecting the negative side of the manometer to the
gas plenum tap. This measurement is taken with the
boiler not firing. It is a temporary setting used to start
the boiler and check for air flow problems.
Figure 17. Gas Offset Pressure.
Figure 18. Gas Orifice Differential Pressure.
Figure 16. Unfired Venturi Differential Pressure.
b. Gas Offset Pressure
The difference in pressure between the venturi
inlet tap and the outlet of the gas regulator (see
Figure 17). This measurement is taken by connecting
the positive side of the manometer to the venturi inlet
tap and connecting the negative side of the manometer
to the gas orifice tap. This measurement is an
indication of the gas to air ratio and must be
performed while the unit is firing.
c. Gas Orifice Differential Pressure
This measurement is the pressure drop across the
gas orifice. This measurement is taken by connecting
the positive side of the manometer to the gas orifice
tap and the negative side of the manometer to the gas
plenum tap (see Figure 18). This measurement in
conjunction with the gas orifice size is an indication
of the gas firing rate and must be performed while the
unit is firing.