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post #8 of Old 11-03-2019
wsmurdoch
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Location: The house is in Kingsport, TN. Boats are on Watauga Lake and in New Bern, NC
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Re: Racor fuel vacuum guages

I too have PSC 34, and I have a Racor vacuum gauge after the Racor 500 filter and before the Walbro electric fuel pump. I also have a 3 way valve between the Walbro fuel pump and the Yanmar fuel pump. That valve can direct the once filtered fuel back to the tank via a tee in the fuel return hose from the injectors, or the valve can send the fuel on to the Yanmar fuel pump and hence to the Yanmar fuel filter, high pressure fuel pump, and the injectors. In the half closed position the 3 way valve can block any flow beyond the Walbro fuel pump.

The three way valve allows me to purge the air from the Racor filter and fill the filter after I have changed the filter element or to "polish" the fuel in the fuel tank by running the Walbro pump with the engine off and circulating the fuel from the tank, through the Racor filter and Walbro pump then back to the tank.

The vacuum gauge serves two important purposes. First, I use it to prove that there are no air leaks into fuel supply system in the parts that are under vacuum. That is done by circulating the fuel from the tank and back to the tank for a few minutes, then closing the fuel supply valve at the tank, waiting until the vacuum gauge reaches a maximum, putting the 3 way valve in its closed position, shutting off the Walbro fuel pump, and waiting for an hour or two for the vacuum in the blocked off parts of the system to break off. With no air leaks the gauge will fall a little as some fuel vaporizes and remain stable after that. Second, I use the gauge to determine if the Racor fuel filter element is dirty. As suggested above I partially closed off the fuel supply valve at the tank to determine the maximum tolerable vacuum and applied a bit of a safety factor to the number. I put a mark on the gauge at that point and keep an eye on it.

Bill Murdoch
1988 PSC 34
Irish Eyes

Last edited by wsmurdoch; 11-03-2019 at 08:55 PM.
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