Exactly how does a bypass valve work?

Patman

Staff member
Messages
21,965
Location
Oakville, Ontario
Thread starter
I'm curious as to how the bypass valve in an oil filter knows when to open? Does it go by oil pressure? If so, wouldn't the use of a thicker oil cause it to open more often? What about those GM engines that have a built in bypass in the block? Do they operate any differently?
 
Messages
1,874
Location
Ocala, Florida
The oil enters the oil filter under pressure through the holes on the perimeter of the base plate. The "dirty" oil then passes through the filter media where it is "cleaned". It then flows to the central tube and back into the engine through the usually threaded hollow center mounting stud.  - Oil Filter Flow Diagram The only thing that holds the "spin-on" oil filter to the engine and keeps the oil from leaking is the base gasket (shown in above picture in red). The Bypass Valve Under ideal conditions, the bypass valve will never open. When it opens, the oil by passes the filter and goes on through to the motor, obviously unfiltered. It is a safety valve. However, in real operation, it opens often. One example is when you start the motor when cold. The oil is thick and does not pass easily through the filtration medium, thus building up to a high pressure drop. So, the bypass valve opens to prevent oil-starvation of the motor. How long it stays open is dependent on how cold the oil is and how long it takes to get near operating temperature. When the pressure drop across the filtration medium drops below the bypass valve setting. Another example can occur when the motor is fully warmed. At idle, the oil pressure is about 15 to 20 psi, and the pressure drop across the filter is about 1 or 2 psi. You take off towards the redline, and quickly build oil pressure. During that full-throttle acceleration the pressure drop across the filter will exceed the bypass setting, and send unfiltered oil to the motor, until the pressure across the filter has time to equalize. During a drag race, shifting through the gears, the bypass will open several times. A third example, which you should never experience with frequent oil and filter changes, is when a filter becomes clogged. A spin-on filter can commonly hold 10 to 20 grams of trash before it becomes fully clogged. The bypass valve opening is the only way to keep the motor from becoming oil-starved if the filter becomes clogged. According to Purolator, the Honda OEM filter bypass setting is 12 to 14 psi. WIX (NAPA Gold) builds their oil filters with a bypass setting of 8 to 11 psi, while AC Delco builds theirs to a setting of 11 to 17 psi. How much do these differences matter? I don't think anyone knows, even the engineers, and each has its own set of advantages and disadvantages. If you do lots of racing, you're probably better off with a higher bypass setting. If you do lots of *cold* starting, especially in the winter, or seldom change your filter, I think you're better off with a lower bypass setting. However, with few exceptions, bypass pressures for spin-on filters run in the 8 to 17 psi range, and any of them should work acceptably. Here is a picture of the breakdown on some oil filters anatomy  - As you can see, some bypass valves are built directly in the middle of the filter while a few do not have one. Here is a cutaway of Bosch's and how each component is located in a filter.  - 1) Rubber seal 2) Steel baseplate 3) Anti-drainback valve 4) The bypass valve 5) Filter media 6) Filter can Hopefully this gives you a better idea about filters and how they flow.
 

Patman

Staff member
Messages
21,965
Location
Oakville, Ontario
Thread starter
Excellent stuff! So with most filters, the bypass will operate when the pressure drop across the filter exceeds that preset limit? Would that mean a thicker oil might trigger it more often like I mentioned in the original post?
 
Messages
60
Location
British Columbia
Yes Patman, thicker oils will cause a higher pressure differental over the filter media but......keep in mind that it is also dependent to some degree on the type of media used. From what I have read, straight cellulose filter media is more restrictive than glass and synthetic filter media for a given performance rating. Can anyone confirm or refute this?
 
Messages
3,346
Location
Clarksville, Tennessee
So one would also argue, that in cooler weather, the by-pass would stay open until the oil becomes thin enough to readily flow through the filter. I can tell a difference in starting my BMW Bike around 50-60 degrees. I'm running 15w40 right now. At around 30 degree, I bet most oils are pretty thick. At what temperature would the oil become thin enough to flow properly? 100 degrees F [I dont know] Is this not one of the biggest benefits to synthetics? Is that they flow more readily at cooler temps?
 
Messages
3
Location
WA, USA
More questions: In various online 'oil filter comparisons' I have read, the bypass valve location shown in the cutaway views of the Bosch filters is considered inferior to valves located at the baseplate end of the filter. The theory is, with the valve located as shown, oil will 'wash' over the filter media when the bypass valve operates, picking up contaminants trapped on the surface of the media and returning them through the bypass valve to the oil pan. I'm wondering if someone can address this. Is this a valid concern? There must be some other advantage to the construction shown in Bob's post that I'm not seeing. Perhaps it's less complex/cheaper from a manufacturing standpoint; perhaps it allows the use of more filter media. Another point: In the SHO oil filter article (don't have a link handy), the author claimed that this type of construction did not meed Ford specifications. Is this true? Do any other manufacturers spec filters with baseplate-mounted bypass valves only?
 
Messages
349
Location
Quebec, Canada
Excellent post, Bob! However, if Patman is correct that if the oil is too thick, the bypass valve will open more frequently - thus - in my Mazda, there is a possibility that my Delvac-1 5W40 is not being filtered. Hence, the possible explanation that my Delvac1 looks dirtier than my Tech2k after only 2000km. This is very interesting indeed. Bob, please confirm this. I'm currently using Delvac1 5W40 where my car is rated to have 5W30 or 10W30 API SH,SG. And, I'm also using a larger Purolator PremiumPlus filter to boot. Thanks, Oz
 
Messages
3,651
Location
Chattanooga, TN
Based upon cutting open several filters I am convinced that even if the bypass were open 50% of the time it would nto make a hill of beans difference in the cleanliness of the oil. How much dirt or wear particles can be created when the filter is in bypass in a well operating engine that would be of the size 10 microns or greater to be captrued by a filter anyway. I think that Terry mentioned on another topic that filters really do not do that much in the overall opeation of an engine and that it is primarily the oil.
 

Patman

Staff member
Messages
21,965
Location
Oakville, Ontario
Thread starter
I know Terry has mentioned that, and I do trust his views for sure, but what about those SAE studies which showed a pretty drastic reduction in engine wear when particles of about 15 microns and less are filtered out?
 
Messages
3,845
The_OZ, your Delvac 1 is dirtier looking because it has more additives that elimminate wear than the Tech 2000. It also is cleaning some of the residue from earlier oils and is being disbursed causing discoloration. Patman, I have said in our tests on bypass filtration that the difference in having one installed vs. Not, in a gasoline engine or smaller Diesel did not justify the costs involved compared to the benefit of reduced wear. Spector got it right, the oil will carry those particles that the full flow misses,safely if it is of good quality. Also if the oil is well formulated you won't be generating that size wear particle (15+ micron) unless something is very wrong.
 

Patman

Staff member
Messages
21,965
Location
Oakville, Ontario
Thread starter
That makes me feel comfortable Terry, knowing I don't really need to spend $12 US for a filter, and can get good results with my Purolators, at just $4 to $6 CDN (for some reason the smaller filter for my wife's car costs more than the humongous filter for my Firebird)
 
Messages
1
Location
IL
would the oil pressure cause the valve to activate just cruising on the highway at around 2000 rpm with clean oil/filter?
 
Messages
3,402
Location
Iowa
Originally Posted By: jramia11
would the oil pressure cause the valve to activate just cruising on the highway at around 2000 rpm with clean oil/filter?
Not likely. I ran a differential pressure test (which is the pressure that opens the bypass) on my engine, just for an example, and the bypass would not start to crack open until at least 3000 RPM with 5W-30 oil at about 180 degrees F. Even then most of the oil would go through the media and be filtered. This is a 2.7 liter 4 cylinder with a small Wix 51348 filter. The oil and filter were clean.
 
Messages
620
Location
Texas
Wow, that's actually sooner then I figured a bypass would open with that kind of oil...especially when clean.
 
Messages
2,264
Location
Texas
Originally Posted By: jramia11
would the oil pressure cause the valve to activate just cruising on the highway at around 2000 rpm with clean oil/filter?
unlikely. Remember that it is the pressure differential that would cause or not cause it to open. That is the difference in pressure on each side of the filter media - the "dirty" and "clean" side of the filter media. pressure differential is not reflected in standard engine oil pressure gauges. | | | V
 
Messages
2,264
Location
Texas
Originally Posted By: river_rat
Originally Posted By: jramia11
would the oil pressure cause the valve to activate just cruising on the highway at around 2000 rpm with clean oil/filter?
Not likely. I ran a differential pressure test (which is the pressure that opens the bypass) on my engine, just for an example, and the bypass would not start to crack open until at least 3000 RPM with 5W-30 oil at about 180 degrees F. Even then most of the oil would go through the media and be filtered. This is a 2.7 liter 4 cylinder with a small Wix 51348 filter. The oil and filter were clean.
cool info!
 
Messages
24,510
Location
PNW
Originally Posted By: river_rat
I ran a differential pressure test (which is the pressure that opens the bypass) on my engine, just for an example, and the bypass would not start to crack open until at least 3000 RPM with 5W-30 oil at about 180 degrees F. Even then most of the oil would go through the media and be filtered. This is a 2.7 liter 4 cylinder with a small Wix 51348 filter. The oil and filter were clean.
I remember your thread about the PSID test you ran. What was the bypass pressure setting on that filter? I'm a little surprised it would start bypassing at 3000 RPM with 5W-30 at 180 F. Wonder if a PureOne would have shown different results. This one only produced ~5 PSID with 12 GPM of flow with 5W-30 at 200 F. http://www.bobistheoilguy.com/forums/ubb...451#Post1619451 I can't imagine the 2.7L puts out as much or more flow then a hi-pro V8 ... but maybe it does. shrug
 
Top