The relief valves can be fine tuned to a degree by shimming to compress the spring slightly, or shimming the cap to reduce spring pressure. Altering the length of the body or the spring can do the same. Swapping out different springs can produce larger adjustments, but Airflow performance relief valves can be expectedto be pretty darn close to target without modification.
I was told today by a Walbro tech that their pumps are NOT, in fact, roller vane but geared, which could explain their higher reliability and their superior self-priming ability. Within a few weeks I will be doing some extensive bench testing on the GSL395 to determine its suitability for Bendix-type FI systems in a dual pump installation, and I will autopsy that pump to verify what I was told today, so at some point there will be an?anatomy a fuel pump, part II? thread.
Btw- the Walbro tech agreed that the published graphs for GSL395 performance are flawed. For example, he looked at the raw data for the 20PSI pressure point, and verified that at 12V flow would be 29GPH but over 40GPH AT 13.5V. The graphs indicate anout 27GPH at 12V and just 19GpH @ 13.5V, which is absurd!
I won?t be bench testing any short-loop recirculation setups because I will be installing fuel return lines to my tanks, but I will heat the Stoddard solvent to 100?F as part of the testing to determine effects of absolute fuel temp on flow dynamics. If I determine that the GSL 395 is inadequate, The obvious choice wil lbe the more powerful, higher pressure GSL393. My ultimate objective is to find the most efficient suitable pump for my needs, with emphasis on range under battery power. Obviously, energy used to push fuel through a relief valve is wasted, so using a 100+PSI pump pushing 40GPM, such as the Delphi obtained from AP or the walbro GSL393 to fuel my 24PSI, <10GPM requirement at most times is contra-indicated. The concern about the GSL395 isthat flow drops off pretty precipitously below 30PSI, so I?ll be focusing upon the 25PSI data point. The Walbro rep did tell me that, if I find performance satisfactory, there would be no harm in operating the GSL395 continuously at 25PSI.- Otis