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Michael LaFleur wrote:
I find it very, very unlikely that both pumps will fail at exactly the same time from debris. Use two filters. The filter before the pump protects the pump and the filter after protects the injectors.
I've picked up contaminated gas at stations, and I know others who have. It's rare, but it happens. I've also known of tanks being vandalized with a handful of sand. Granted, that was high school, but do vandals ever grow up? I think the question hinges on how long you think a pump can handle a slug of trash or water. From the drawings I've seen of how the pumps work, there is very little clearance for anything but clean fuel. I don't see a problem with micron sized particles killing the pump, but there isn't much margin once you break into the visible range. The problem is compounded by pickup schemes that draw from a blister in the bottom of the tank, which effectively insures that all the contaminants are driven directly to the pump. So, the running pump draws in some trash and quickly gives up the ghost. The engine hiccups, I get nervous and kick on the second pump, draws in some of the same trash, and dies just as quickly.
Al W. doesn't think the pumps are at risk, but he does think there is a serious issue with vapor lock which argues against the filter before the pump. My logic is that I don't trust the input. I don't trust the gas from every station and every can that I will ever draw from to be clean and dry, even if it looks that way before I pour it in.
Al is right that we're all just pushing wind until we have some actual measurements. I'll have a system installed in just a few weeks. I'll rig up a test system to measure head loss, vapor pressures, and determine what happens when a slug of water hits the pump.
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