seasick said:
The issue is not filter size, it is maximum fuel flow rate. As long as the flow rate is greater than the demand, all is OK. Calculating the actual flow rate is not a simple task. You start with the flow rate of the filter ( often in the area of 90 GPH more than sufficient) and then subtract for fuel fittings, line size, line length etc.
The bottom line is that the filter size does not have a direct bearing on flow rate. So if all seems OK, don't go looking for problems, there may not be any. Other than the need to carry two different sized spares, there is probably no other issue.
I am sorry but there is some bad info here so let me go thru this post.
"As long as the flow rate is greater than the demand, all is OK" Not always true, the flow rate is always associated with a pressure thru the media, if the stock filter is rated at 90 gpm at one pressure loss, and an aftermarket one is rated at 90 gpm at higher pressure loss all might not be okay.
"You start with the flow rate of the filter ( often in the area of 90 GPH more than sufficient) and then subtract for fuel fittings, line size, line length etc." You dont subtract fittings and line sizes from flow rates. The pumps are capable of moving a certain volume of fuel at certain pressure, the volume is dependend on system pressure losses, this is actualy plotted on a pressure vs flow curve. All of the components, including the filter, are system pressure losses that are culmitive. You add up all your losses and compare that to the flow rate of the pump at that pressure.
"The bottom line is that the filter size does not have a direct bearing on flow rate" Again not realy true, media area has a direct corrolation to flow rate. More media area higher flow rate at the same pressure loss, or more media less pressure loss at the same flow rate.
"So if all seems OK, don't go looking for problems" I agree 100%
I am sorry just like to keep everyone honest.
Tim