Hi, Brian: As you know, I'm reticent to put forth an opposing point of view, but here goes: Racor recommends 30 or 10 micron primaries with a 500-hour change interval; Lugger recommends changing the secondary at 600 hours. Based on experience, I believe that's conservative, and so I go about twice that. Of course, I buy fuel from trusted sources. Last October, I changed the 30-micron Racor primaries and the Lugger (Wix) 2-micron on-engine filter. Now, 813 meter hours and 2195 gallons of fuel later, I am still on the same filters, and have yet to switch the primary over. The gauge on the Racors reads the same as it did last fall. Regards, John "Seahorse" Hello John Of course good maintenance prevents problems. But when designing a system you should consider the possibility of a bad load of fuel or some crap getting stirred up in rough conditions. Even the very best of maintenance won't prevent that and in that situation I would prefer to be able to glance at a vacuum gauge know the overall condition of the fuel system detect a problem early and know exactly where it is. Brian Palmetto FL