I doubt the bypass valves operate like an on or off switch, especially the coil spring type. I’m sure it just bleeds off excess pressure. I agree that you would probably not see a change in the pressure drop under this scenario.
The leaf spring type valves might be a different story though. For all I know, they might be an on/off type of pop valve. It’s conceivable that you might be able to observe a momentary blip in the pressures.
Regarding the valve operation, it seems to me that each valve would operate differently depending on how restrictive the media is and how much surface are a filter has.
Take for example three examples of the basic Ford F1a filter. I use Wix part numbers in this example. Part number 51515 is the equivalent part for the F1a filter. 51085 is the short version, and 51773 is the very long version. Here are their heights (other dimensions are the same:
51085 3.790 inches
51515 5.178 inches
51773 6.980 inches
Each has an 8-11 lb. pressure relief valve. I’ll assume the smallest has the least media and correspondingly least surface area, and the largest has the most media surface area. Under identical conditions, the filter with the more media should have a lower pressure drop differential, and probably has a wider flow rate rating between the pressure drop (i.e., can accept more flow and will have a lower drop in pressure than a similar, but small filter). In other words, the larger filter with more media would go into bypass mode less often than the small filter. I wonder if the valves are indeed the same and If the larger filter has more media surface area, or just less pleats than the smaller filters.
I also wonder if the pressure relief valves in two OEM replacement filters made by the same company, say Champion Labs, would operate in the same manner. Would a M1 filter open its valve sooner than a K&N filter because its virgin pressure drop is already closer to the valve resistance setting, or have the valves been compensated in each application (using different parts) so that the valve opens say 8-11 lbs below the virgin drop?
Just some food for thought.
The leaf spring type valves might be a different story though. For all I know, they might be an on/off type of pop valve. It’s conceivable that you might be able to observe a momentary blip in the pressures.
Regarding the valve operation, it seems to me that each valve would operate differently depending on how restrictive the media is and how much surface are a filter has.
Take for example three examples of the basic Ford F1a filter. I use Wix part numbers in this example. Part number 51515 is the equivalent part for the F1a filter. 51085 is the short version, and 51773 is the very long version. Here are their heights (other dimensions are the same:
51085 3.790 inches
51515 5.178 inches
51773 6.980 inches
Each has an 8-11 lb. pressure relief valve. I’ll assume the smallest has the least media and correspondingly least surface area, and the largest has the most media surface area. Under identical conditions, the filter with the more media should have a lower pressure drop differential, and probably has a wider flow rate rating between the pressure drop (i.e., can accept more flow and will have a lower drop in pressure than a similar, but small filter). In other words, the larger filter with more media would go into bypass mode less often than the small filter. I wonder if the valves are indeed the same and If the larger filter has more media surface area, or just less pleats than the smaller filters.
I also wonder if the pressure relief valves in two OEM replacement filters made by the same company, say Champion Labs, would operate in the same manner. Would a M1 filter open its valve sooner than a K&N filter because its virgin pressure drop is already closer to the valve resistance setting, or have the valves been compensated in each application (using different parts) so that the valve opens say 8-11 lbs below the virgin drop?
Just some food for thought.