Usage:
All Caterpillar Engines
Most mechanical pressure gauges, like those found in premium instrument panels, have one or more orifices. These orifices dampen the pressure pulses to reduce wear in the internal linkage of the gauge. The orifices are found either in the gauge itself or in the pressure line to the gauge.
As an example, two small brass orifices are threaded inside of the pressure connection of a 4W506 Pressure Indicator. Another example is found in the junction block mounted under the instrument panel as part of the pressure lines. See the illustration showing a cross section of the junction block.
Cross section of junction block.
Orifices are located in the ports for the tube assemblies connected to the gauges.
When troubleshooting this style of gauge for low or erratic readings, check for plugged orifices. Some gauges, which have been replaced, are found to function correctly after cleaning out a plugged orifice.