A Short Cruise on Understanding Gauge Readings
On A Fuel Filter Restriction Gauge
RK11-1669      Racor T Handle Kit
Many different variables in your fuel system will affect the readings on
your Gauge, here are some of the following results

Higher Readings                                    Lower Readings

The use of a fuel strainer on                   Dirty secondary fuel filter
the pick up tube in the tank.   
                                                          High level of fuel in tanks
Undersized  fuel Lines
                                                             Worn fuel pump
Fuel valves not fully open
                                                            New Primary filter
Blocked fuel tank venting
kinked hose or Bees or other
insects in the overboard screen
(check your Fire Extinguisher
Hose ends weekly)

Fuel hose inner liner collapsed

New secondary fuel filter

Lower fuel level in tanks
Lifting Fuel up to the engine  
1 Foot of lift will increase the
Reading by  .8861 " Hg

Dirty Primary fuel filter

Fuel Gelling (very cold temp.)

As you can see a Fuel Restriction Gauge is more than just for checking
the condition of you fuel filter. Readings should be taken at cruising
RPM and load or higher. Also keep in mind some engines use the fuel
flow in the system for cooling of the injectors and pump. Even though
the engine is running good you could have a improper fuel flow.
Check with your engine dealer for
maximum fuel vacuum specifications for
your engine or equipment. Color bands on our gauges are for visual
reference only!
Most Diesel engines use a mechanical fuel pump (lift pump) this will
cause the needle to vibrate at times (these pump in Pulses) . This will be
amplified at idle if there is a high reading. This is one of the reasons a
liquid filled gauge is best suited for this application, liquid dampens and
lubricates the gears inside.  Dash mounted (hose run dampens) and
gauges with a restricter (
some of our gauges come with this) will also
dampen this effect.
With the proper valves it can also be used to check for any leaks in the
suction side of the system.
 Most filters elements need to be changed
with readings of "4 7" to 10", at 12" depending on fuel temperature, air is
sucked out of the diesel fuel.

                                    Designated Engineer
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and other fuel filter restriction gauges
See Notice On Cummins QS Series
and Drag Pointer and Readings
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as on Racor Models 500 900 & 1000
Turbine Series fuel filter / water
separators   fuel filter promblems