Notching Drain Lines?

Is this what you’re looking for?

Yes! I was looking in section 73... Thanks!

Hi Michael,

The concept is simple the application not so.

Concept

You don't want a vacuum, being transmitted up the hose, to the system it is venting/draining.

A vacuum (low pressure zone) is likly in the area just behind the cowling where the air exits.

You are advised to have your vent lines exit overboard (behind the cowling where there may be a vacuum).

Make a hole (cut a notch) in the vent tube in a higher pressure (than behind the cowling).

The hole will allow high pressure in, to counter any vacuum created.

Applicating

Problem - where to cut notch in high pressure area???????

My solution - T piece in end of vent hose.

Using leg of T, connect & run a second vent hose to high pressure zone - in my case  top of firewall.

Job done - no chance of vacuum being transmitted to system😈

I may have been using "vent" and "drain" lines interchangeably....  These are the fuel drain lines from the fuel pump, drip trays, and airbox.  Maybe they should not be notched?

These "whistle" notches also function as a pressure relief point for crankcase breather vapors in the event the exit end of the breather line is plugged up with frozen crankcase vapor (i.e., ice plug).  Perhaps such thinking could also apply to other types of overboard vent lines?  The potential presence of freezable water in the specific exit stream may be a design consideration??