Well, er, ah, oh,,, Dual Racors usually run one at a time. If you have a dual system, you can push them further if your equipped with a tell-tale low pressure gauge. AND if you have low pressure gauges after your secondary fuel filters, can help them last longer instead of guessing hours. Just the history of what you have been finding in the mud (Racor) filters can help the future filter service. So, what has your mud filters been looking like before?
With dual racor i use one at a time. At oil change i replace the one that was used and switch to the other one.
low pressure = vacuum Vacuum is a state of pressure below atmospheric. However, for those in Rio Linda, I'll try to use the word Vacuum in the future.
You don't measure vacuum with a pressure gauge or vice versa.... on your primaries you are measuring vacuum (negative relative "pressure" vs atmo) or "suck" on your secondaries before the lift pump; the pressure (positive vs atmo) gauge is after the lift pump, measuring "blow". Surely everyone here understands the difference between "suck" and "blow".
A vacuum gauge is a pressure gauge used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (e.g.: -15 psi or -760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure". However, anything greater than total vacuum is technically a form of pressure. For very accurate readings, especially at very low pressures, a gauge that uses total vacuum as the zero point may be used, giving pressure readings in an absolute scale. https://en.wikipedia.org/wiki/Pressure_measurement
Well you just stick to your call them "pressure gauges" when everyone else, including Racor, calls them vacuum gauges http://www.parker.com/parkerimages/Racor/7700 (11-1676E Vacuum Gage).pdf https://www.sbmar.com/product-category/fuel-systems/vacuum-gauges/
Semantics... Marine engineers are taught that any fluid system under vacuum is known as the low pressure side of the system. Discharge side is known as the pressure side of the system. Your getting a bit caught up in the semantics of terminology and thankfully you weren't put on blast for your tongue in cheek post # 10.