Selection of a check valve -Fuel return line

I can marginally under stand why they suggest a check valve to bypass pressure in a closed system with a Returnl Fuel Valve in the Upper example.

Wth a single Fuel Valve and an alway open retun line, the only need for a check valve would be to prevent fuel from draining out the return hose in the event of a catastropic accident where the return hose becomes severed.

It would appear that any low value check valve that prevents reverse flow would be sufficient.

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In reviewing the diagrams, in all the other installation examples, fuel WILL backflow through the Dual Fuel Valves if the event of severed hoses Unless the Fuel valves are manualyl closed.

So why is the check Valve Specified ??? Safety Third!

Andair make very nice check valves. My installation uses one after the header tank.

Ray,

The pressure of the valve in the location you reference should be .4-.7 PSI, not bar. This is corrected in a later version of the Rotax installation manual.  Andair makes part number CK375M for this application, and I would imagine there are others.  In a single tank system the check valve is directly in the return line and needs to be low pressure so that the pressure on the return line does not exceed 7.25 PSI (.5 bar) with both pumps running.

When a dual selector valve is used to direct the supply and return flow simultaneously, that negates the need for this particular check valve.  However, there is a check valve used along with a dual selector valve, but for a different purpose.  In this case the check valve is not directly in the return line but rather in a high pressure bypass line which provides a safety outlet in the event the fuel pumps are accidentally run with the selector valve off.  You can see this application in the illustration directly below the one you reference. Andair sells part number CK375-MM-14-BRP for this application and it’s important you don’t select this higher pressure valve for the location you are referring to.

Hi Jeff,

A big thank you for the correction, bar to psi. You are right, it is corrected in IM 915iS as .0276-.083 bar, but the latest 912iS Installation manual -Feb 2020 version still showing .4-.7 bar.  

Jeff, could you help me with details of Andair CK375M which you are suggesting for this low pressure application? Not finding in their website.

Thanks again & best regards,

Ray

Hi Geoffrey,

Many thanks. Could you please send me the Andair part no. of the check valve you are using/ recommending?

Ray