Can anyone explain the basis of the check valve for fuel return line to be as per engine manufacturer requirement instead of being a hard requirement in NFPA 20?
11.4.4.3.1 A check valve, as specified by the engine manufacturer, shall be permitted to be installed in the fuel rentrn line only when required by the engine manufacturer.
I would guess that the engine manufacturers contributing to NFPA 20 could not agree on the specific content, and wanted to preserve their own individual design freedom.
This popped up on radar this morning. The above capture from this DISCUSSION is one example where several conditions can cause this.
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My guess is this check valve requirement on "fuel supply pressure recycle return line to fuel tank" is valid only when BOTH of the following are applicable
a)the return line enters the fuel tank below the max permitted normal diesel fuel level in the tank
b)the fuel tank max liquid level is above the elevation of the fuel supply return line at the point where it enters the diesel engine
One supplier of ours that uses John Deere engines has strict back pressure limits on the fuel returns. We have to run checks because we have multiple engines sharing common returns.
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