Legacy Fuel Flow Gauge

[Rob58]

On older aircraft with fuel flow gauges that are actually pressure gauges there are typically two ports, "P" & "V". I am assuming that the P port is the pressure port, but not sure what the purpose of the other port is?

 

[Timbeck2]

Velocity? Volume?

 

[Capt. Geoffrey Thorpe]

uVer side of the orifice?

For an orifice flow meter, you want to measure the pressure on both sides so you can use the orifice equation to calculate flow.

https://en.wikipedia.org/wiki/Orifice_plate#Description

 

[Ryan Klems]

It’s “vent” on a turbo that’d be upper deck pressure, on a NA usually static or cabin ambient.

 

[Rob58]

Very interesting suggestions... let me provide one additional piece of information. On my plane the "V" port is not connected to anything, nor is it plugged - just an open port. If it is supposed to measure static pressure is it intended to tie into the static circuit or at least have a filter?

 

[Ryan Klems]

I’d look at your IPC or MM for the aircraft. For a normally aspirated engine, that’s not uncommon for it to be open to ambient cabin pressure. Some systems are plumbed in to static for the vent. It’s whatever the reference is for the pressure gauge as specified by the manufacturer.