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Vacuum Monitoring of Diesel Fuel Systems


Vacuum gauges and alarm switches, shown above, are used to monitor your diesel fuel system, including the filter element. As the element becomes clogged, fuel flow becomes more restricted resulting an increase in vacuum on the engine side of the fuel filter.

A vacuum gauge can be used for more than just checking the condition of your fuel filter. Many variables in your fuel system will affect the readings on your gauge. Here are some examples:

Some possible causes for
high readings:

Some possible causes for
low readings:
  • Dirty Primary fuel filter
  • High density filter media being used (2 micron filter cartridge. 30 micron is recommended)
  • The use of a fuel strainer on the pick up tube in the tank
  • Undersized fuel Lines
  • Fuel valves not fully open
  • Blocked fuel tank venting kinked hose or
    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
  • Fuel Gelling (very cold temp.)
  • Dirty secondary fuel filter
  • High level of fuel in tanks
  • Worn fuel pump
  • New Primary filter
Other Tips:
  • Readings should be taken at cruising RPM or higher while under load. The drag point feature really comes in handy because it remembers the maximum vacuum.
  • Some engines use the fuel flow in the system for cooling of the injectors and pump. Even though the engine is running well, you might have a improper fuel flow. Check with your engine dealer.
  • Most Diesel engines use a mechanical fuel pump (lift pump), which will cause the needle to vibrate. Dash mounted (hose run dampens) and gauges with a restricter 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.
Find our vacuum products in our Engine Room.

Click here for Racor marine filter information.
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