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Oil/Fuel Restrictor Fittings Needed?

Karetaker

Well Known Member
Howdy Everyone. I have the GRT remote R66 EIS. The fuel and oil senders have 1/8" NPT male threads and a very tiny hole. With these senders, are the restrictor fittings shown in the plans required?

Much obliged.
 
Howdy Everyone. I have the GRT remote R66 EIS. The fuel and oil senders have 1/8" NPT male threads and a very tiny hole. With these senders, are the restrictor fittings shown in the plans required?
Much obliged.

The restricters are to minimize oil and/or fuel loss in case of a line or sender failure. Not required but highly recommended.
 
Same for manifold pressure. A restrictor in the primer port fitting prevents that cylinder from going very lean if the hose comes off or is cut.
 
In case it isn’t clear to later readers of this thread, the restrictor fittings go on the engine. I point this out because I witnessed a restrictor fitting at the remote sensor. IIRC it was the fuel sender too. Ugg.
 
Secondary effect(s)

The restriction dampens pressure ripple; common with PD pumps like oil pumps. Besides steadying the readout, it will prolong the life of the sensing element.

I had always made the assumption from steam gage times, the restrictions also lessened other consequences. Analog cockpit gages are sensing the actual fluid pressure at the device. Imagine dumping 60 psi oil or 30psi fuel (no flow restriction) into the cockpit. If this assumption is in error, someone let me know.
 
When 306 hose and reusable hose ends were commonly use for fuel pressure and oil pressure lines, over time they have a tendency to develop cracks and leaks, especially under vibration and engine movement. So using a restricted fitting did lessen the amount of fluid loss if the hose failed.

With the use of teflon, with its higher fluid temperature capabilty and higher working pressures, not to mention its resistance to most all chemicals, hose assembly failures have become rare. So restricting the fittings is now common to dampen the pressure pulses for modern avionics sending units. Some have gone to using -3 hoses with .079 ID hose end stems without restrictors with excellent results.

Tom
 
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