vacuum gauge with Racor filter

[flechenbones]

Originally Posted by RichH

It all depends on the mechanical strength of the lift pump and how much it can 'suck' when 'deadheaded' (totally blocked flow).

I may be incompetent, but I can't seem to find that information. This is the lift pump.
Facet Cylindrical Solid State Electric Fuel Pump - 476459E - Discount Yacht Supplies, Vetus Nautical Accessories, Scandvik Parts, Garmin Marine Electronics

[RichH]

Not a problem
"1 - 8 psi" ... use the 8 psi as the deadheaded ("0" flow or max.) pressure.

8 psi = 16" of hg. pressure or vacuum.

Nice pump.

[rikhall]

Originally Posted by MacGyverRI

There's no need to waste money on that fuel gizmo, just watch the RPM's.

I have had problems with restricted filters three times and none of them was reflected in low RPMs. I am baffled as to why not, but such was the case. I lost speed with the same RPMs. Made no sense at all.

Rik

[RichH]

Originally Posted by rikhall

I have had problems with restricted filters three times and none of them was reflected in low RPMs. I am baffled as to why not, but such was the case. I lost speed with the same RPMs. Made no sense at all.

Rik

Assuming that you have a diesel engine, several things could have occurred.
1. most particles in diesel fuel are 'deformable' and can 'extrude' though filters under increasing differential pressure/vacuum across a filter ... the filters may have 'unloaded', yet retained the correct µM rating for 'hard' particles.
2. It takes 'work' (differential pressure across a filter) to filter and you may have had sufficient flow capacity at the lower rpm demand, but not the higher rpm demand due to the 'partial' plugging of the filter(s). Thats why my usual recommendation is to change at about 75% of maximum vacuum/pressure ON THE GAGE (75% of what the lift pump can 'suck' at maximum) when 'tested' with the engine running at wide open throttle (WOT) .... ensure you have enough 'dirt capacity' still left in the filter or to discover WHEN to change it. Its easy to determing max. vac./pressure output of the lift pump... simply close the tank valve and watch the gage for its maximum reading. Then you know to quickly change the filter(s) when the gage gets to 75% of that max. lift pump value. ;-)

[flechenbones]

Thanks Rich. I guess that means that the red "change filter" indicator on the R2D2 guage beginning at 10 hg is fine considering you think that it should be changed by 12 hg.

[RichH]

All depends on the 'deadhead pressure' of the pump, then I recommend the changeout @ 75% of max. If max. is 10" then change out @ 7.5"; if max is 8" then change at 6", etc. etc. All depends on the pump.

[flechenbones]

Understood. I arrived at 12" hg by 75% of 16" hg.