These meters have no downstream and shorter upstream straight pipe requirements for standard accuracy, have lower head-loss, and are less susceptible to blockages and plugging as the annular chamber was replaced with a single pressure tap
Placing an outdoor pressure tap
on the roof, however, helps confirm that the entire building is either pressurized or depressurized so that the air flow is either all into or out of the building for each test period, and that stack effect is not introducing unmeasured airflows due a change in interior pressures.
Figure 2 shows a single chamber orifice meter with a downstream pressure tap
and an extra DP transmitter.
When the impeller was pumping upward the fluid velocities near the pressure tap
increased thus reducing the pressure readings as the impeller speed was increased.
The problems of centering the plate, alignment of the inlet and outlet piping, and pressure tap
to plate dimensions have also been solved using standard fittings and patented plate holder designs.
As mentioned, the conventional pressure tap
approach provides good information.
Were both the downstream and upstream pressure tap
distances varied to determine the effect or were they maintained at the SPC 120 recommended length of 11 diameters?
Note that the side pressure measurements were routed to the top of the pressure tap
sleeve, as described in Figure 5.
The flow measurement also showed a 20% under-prediction of flow, indicating possible sensitivity to the pressure tap
Pressure drop measurements were obtained with an Invensys IDP10-T differential pressure transmitter connected to a pressure tap
located 50 mm (2 in.
The kitchen pressure tap
was located on the right-hand wall that served as the symmetry plane for the hood 48 in.
The capillary tube diameters and the pressure tap
diameters were measured with the help of a tool maker's microscope.