Quote:
Originally Posted by Samuel M. Ross
These same restricted orifices also serve to minimize interactions between systems… e.g. the A/C causing an unwanted shift of the transmission. So along come mechanics and owners who correctly clean out the “guck” and crud that ends up clogging these “T”(s) and inline orifices and in some cases they also drill out these “T”(s). The white “T”(s) on the two 1980 cars I show below are about .8-to-.9mm in size and I have seen on this FORUM people recommending they be drilled out to 1/16 inch which is ~1.6mm… and such a dramatic change in size of these IMPORTANT restricted orifices clearly can upset the balance that was designed into these cars… balance that gives the BRAKES their needed priority over other vacuum users… and balance that prevents interaction between unrelated vacuum using systems… the tranny and the A/C.
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The purpose of the restricted orifices is to isolate the components downstream of the restriction from the brake system. If there is a failure in a vacuum pod for the climate control or a failure in the EGR valve, the restriction prevents the main vacuum line from dropping too low in vacuum. Most of these consumers use very little airflow and a .9mm orifice is sufficient provided one is willing to wait 15 seconds or so for complete actuation. The time is not a factor for these devices so the system works as designed.
If you were to remove the orifices completely from the system, the system would still function perfectly well, with no interactions between the various systems, provided that there were no leaks in the system.
The sole purpose of the restriction is to prevent a leak from dumping vacuum from the brake system. The size of this restriction is not magical. It depends on the capability of the vacuum pump. If you open a .8mm restriction to 1.6mm, you get 4X the flow, however, this flow is still insignificant when compared to the 6mm?? I.D. of the main vacuum line. I seriously doubt that a wide open 1.6mm restriction would drop the main line vacuum more than 1" of vacuum......or so.
A quick test of a wide open 1.6mm restriction on the main line would confirm or deny this theory.