Non Bypass Oil Filter Oil Starvation

[proppastie]

High pressure outside the filter element very little blockage (new filter) spring counteracts pressure drop across the pleats? ......Blockage....pressure drop across the pleats of the filter element is higher than the spring pressure?

 

[wsimpso1]

The larger area opposite the inlet/outlet cap against the area at the inlet/outlet implies, to me, that the oil pressure against clogged media would force the filter more tightly against the cap, not open it for relief.

I spent years in the air brake component remanufacturing industry and did numerous analyses of the internal pressures of compensating valves, self-releasing control valves, regulators and actuators. This pressure relief spring arrangement puzzles me some. What am I overlooking?

The filter element is held on a seat with a spring. Oil comes from the pump to the central port on the filter end cap, and enters the inside of the filter element. Normal operation is oil passes through filter paper to the space between filter and outer can, out of the peripheral port of the filter assembly, then to the cooler and pressure galleries. If force across the filter element exceeds the spring force, the filter is forced off the seat, unfiltered oil bleeds out the gap, out the filter assembly and to the cooler and galleries. No valves, just a spring holding the filter element against the end cap.

Billski

PS - Look at posts 17, 20, 25, and 27 by Dan. He covers this all way better than I and covers it correctly.

 

[TiPi]

As I understand it, the bypass is for cold starting if the oil is very viscous, but I have no idea what's a realistic pressure drop through the filter.
Assuming 50 weight oil at -5 degrees C compared to 110 C, that's a fair viscosity difference.

That depends
Oil classifications are quite complex. The grade/weight given to an oil is based on several measuring points:
100deg C, 40deg C and at a cold temperature related to the pour point or cold cranking simulator.
The viscosity changes from 100-200 cSt at 40deg to 8-20 at 100deg.
At temperature below 40, the viscosity is increasing exponentially, controlled by the base oil and additives.
Between 40 and 100deg, most oils have a slight exponential curve, captured as the viscosity index.
Above 100deg, same grade oils can behave very differently based on their base oils, refining and additives (and additive depletion/oxidation/changes in pH)

 

[TiPi]

The filter element is held on a seat with a spring. Oil comes from the pump to the central port on the filter end cap, and enters the inside of the filter element. Normal operation is oil passes through filter paper to the space between filter and outer can, out of the peripheral port of the filter assembly, then to the cooler and pressure galleries. If force across the filter element exceeds the spring force, the filter is forced off the seat, unfiltered oil bleeds out the gap, out the filter assembly and to the cooler and galleries. No valves, just a spring holding the filter element against the end cap.

Billski

Sorry Billski, need to disagree. The pressure difference between the outside and inside results in an increase force of the filter element against the canister head (average plate circle cross section x pressure difference).
My understanding of the bypass valve (not the mechanical spring-loaded check valve in the bottom of the filter element) is that the rubber disc works as a back-flow check valve and an over-pressure bypass valve.
Most filters have a wide range of bypass specs, ranging from 8-20psi for some of the smaller spin-on filters.

 

[Dan Thomas]

The filter element is held on a seat with a spring. Oil comes from the pump to the central port on the filter end cap, and enters the inside of the filter element. Normal operation is oil passes through filter paper to the space between filter and outer can, out of the peripheral port of the filter assembly, then to the cooler and pressure galleries. If force across the filter element exceeds the spring force, the filter is forced off the seat, unfiltered oil bleeds out the gap, out the filter assembly and to the cooler and galleries. No valves, just a spring holding the filter element against the end cap.

Billski

Nope. The oil passes from the outside to the inside. The outside is what we looked at to see what debris was being collected. The outside has no cage around it, but the inside has a perforated tube to prevent collapsing of the media under pressure.





From https://www.championaerospace.com/wp-content/uploads/2015/06/AV6-R-Aug20141.pdf

I'm beginning to wonder if the spring is just a method of taking up slop due to small variations in can depth and cartridge length, not as a relief valve. In the picture above I see a spring-loaded relief valve inside the cartridge. When we cut the media off to spread it out for inspection, we just tossed the center core. Never looked inside it. Strange.

 

[PMD]

The filter element is held on a seat with a spring. Oil comes from the pump to the central port on the filter end cap, and enters the inside of the filter element. Normal operation is oil passes through filter paper to the space between filter and outer can, out of the peripheral port of the filter assembly, then to the cooler and pressure galleries. If force across the filter element exceeds the spring force, the filter is forced off the seat, unfiltered oil bleeds out the gap, out the filter assembly and to the cooler and galleries. No valves, just a spring holding the filter element against the end cap.

Billski

I have to agree with Dan. The pressure on the surface of the end cap by the spring is the same as the pressure against the opposite end cap where the element seats against the base plate - except there is MORE surface area at the spring end, increasing the seating pressure of the element assembly against the base as delta P across the element increases. Also, when calculating values you can not assume the element is at the diameter of the end plates, it is centered at some medial radius between the inside dia of the support tube and the outer diameter of the end caps as the pleats go down to that level with a space on either side (mess of little triangles with external i.e. inlet pressure on the outer rows and internal i.e. discharge pressure on the internal rows). That pressure attempting to spread the two end caps apart is the same top and bottom and must be subtracted from the pressure on the outside areas of their respective caps. The only way this could lift the element off of the base would be with an effective seal between the outer diameter of the spring-end cap and the canister.

 

[DanH]

Choosing a filter with or without a pressure relief valve depends on the choice of filter adapter.

Classic AC-style filter adapter for Lycoming: pressure relief is in the adapter, not the filter.

Several popular aftermarket adapters (two examples below, a straight Superior and a right angle, possibly B&C) have no pressure relief provision, as do many Continental applications. They require a filter with a built in pressure relief, specifically (Champion #s for reference) CH48108 or CH48109. That valve is a coil spring type, located in the element end cap, photo below. It's not the flat spring.

 

[DanH]

The filter element is held on a seat with a spring. Oil comes from the pump to the central port on the filter end cap, and enters the inside of the filter element. Normal operation is oil passes through filter paper to the space between filter and outer can, out of the peripheral port of the filter assembly, then to the cooler and pressure galleries. If force across the filter element exceeds the spring force, the filter is forced off the seat, unfiltered oil bleeds out the gap, out the filter assembly and to the cooler and galleries. No valves, just a spring holding the filter element against the end cap.

Billski

Nope. Oil is delivered to the outside of the pleated element. The flat spring merely locates the element in the can. As noted previously, filters designed with a pressure relief (108 and 109) have a spring loaded poppet valve in the end cap, spec being (IIRC) 12 to 15 psi.

 

[Pops]

I had an oil filter on the SSSC for a few years. Had the high pressure relief valve ( on the flywheel end of the case in the VW) set for 60 lbs. On start up the rolled top of the filer came loose. It was a defective filter where the roll at the top was about 1/2 done. Look on Dan's cut away of the filter.
I'll just keep changing the oil at 25 hrs and not have to worry about it happening again.

 

[Dan Thomas]

Choosing a filter with or without a pressure relief valve depends on the choice of filter adapter.

Classic AC-style filter adapter for Lycoming: pressure relief is in the adapter, not the filter.

Several popular aftermarket adapters (two examples below, a straight Superior and a right angle, possibly B&C) have no pressure relief provision, as do many Continental applications. They require a filter with a built in pressure relief, specifically (Champion #s for reference) CH48108 or CH48109. That valve is a coil spring type, located in the element end cap, photo below. It's not the flat spring.

Good stuff. Thanks. I installed a bunch of those Superior adapters, or a similar version, on the school's Lycomings. Much easier to deal with than the screen, and kept the oil a lot cleaner.

 

[wsimpso1]

I stand corrected. I have not looked in detail at a filter in a long time, and it shows. Egg on face. Just came from the FBO maintenance hangar, and looking at filters they have there, several things became obvious:

• Oil does travel from outside to inside of aircraft filters - I had somehow gotten it in my mind that the oil traveled the other way around - debris is always on the outside of the paper, not the inside. I have also heard that a few engine manufacturers do flow inside to outside, but not Lycoming, Continental, Rotax;
• The filter is held on the seat of the housing end cap by both the spring (whether flat or coil) and by pressure drop across the filter element;
• Many have a pressure relief valve buried in the filter element end cap to ensure flow to the rest of the engine when delta P across the filter is too high. Dan covered this really well.

I shall edit my posts and promise to stick more closely to things I know better...

Billski

 

[BJC]

I shall edit my posts and promise to stick more closely to things I know better...

Several times I have considered that myself, but then realized that I would have to stop posting.


BJC

 

[proppastie]

The outside is what we looked at to see what debris was being collected.

I have stopped cutting the pleats and spreading flat ......I just look between each one for chunks of metal....any thoughts?

 

[DanH]

I have stopped cutting the pleats and spreading flat ......I just look between each one for chunks of metal....any thoughts?

Given that Lycoming guidance measures debris with a teaspoon...

I jest, but only slightly. The actual guidance is grounding if a 1/2 teaspoon or more. If only 40 or 50 pieces, it's clean the screen, install a new filter, and ground run it for 20 minutes, and inspect again.

Point is, yes, a fella can probably spot trouble just looking between the pleats.

A surprising number of mechanics fail to clean the sump screen. It should come out for a look at least every other oil change.

 

[Dan Thomas]

I have stopped cutting the pleats and spreading flat ......I just look between each one for chunks of metal....any thoughts?

I cut the media out with a sharp knife, spread it out and checked for big bits, then rinsed it in solvent to see what fine stuff was there. Gently poured off the solvent and ran a magnet through the remaining sediment to see how much of it was iron.

 

[proppastie]

to see how much of it was iron.

so how much is too much 1/2 teaspoon?......one guy says you get a little bit of metal always....another says he get none.......Running a small magnet between the pleats I currently get a little bit.....and the oil analysis people when I sent in my filter said "trace".......but having seen spalled followers and wiped cams...I do wonder....... wait until loss of performance to deal with it?

 

[Marc Zeitlin]

so how much is too much 1/2 teaspoon?......one guy says you get a little bit of metal always....another says he get none.......Running a small magnet between the pleats I currently get a little bit.....and the oil analysis people when I sent in my filter said "trace".......but having seen spalled followers and wiped cams...I do wonder....... wait until loss of performance to deal with it?

Suggestions if Metal is Found in the Screens or Filter

Because the failure to look for metal in the screens and filter, or ignoring what is found, can lead to catastrophic engine failure, we’ll attempt a logical approach to the proper action to be taken

www.lycoming.com

https://www.lycoming.com/sites/default/files/SB480F%20Oil%20ServicingMetallic%20Solids%20Identification%20After%20Oil%20Servicing%20and%20Associated%20Corrective%20Action.pdf

 

[proppastie]

I have read all the guidance out there .......my question is related to others subjective experience and response......especially those with fleet maintenance experience.....My 5 overhauls hardly qualify......it is hard now days to find the local shop that will do a IRAN or overhaul because of liability issues. what a shame.

 

[Dan Thomas]

so how much is too much 1/2 teaspoon?......one guy says you get a little bit of metal always....another says he get none.......Running a small magnet between the pleats I currently get a little bit.....and the oil analysis people when I sent in my filter said "trace".......but having seen spalled followers and wiped cams...I do wonder....... wait until loss of performance to deal with it?

You should get a little bit of fuzz. Anything up to a pea-sized ball I didn't worry about. There isn't much iron in a peas-sized ball of fuzz. It comes from rings and cylinder walls, mostly, since those things are constantly wearing.

Spalling will produce flakes of steel. That's more alarming. Flakes of aluminum often come from piston pin end plugs. They keep the pin centered in the piston, and get shaved when the cylinder wears enough to develop a sharp ridge at the bottom of the ring travel. If there's no ring below the pin on the piston, that ridge will shave the plugs. I used to see that in engines that suffered cylinder wall corrosion from running too cool and/or short flights.

Bits of bronze come from the rocker and rocker shaft bushings, usually. The wrist pin bushing in the rod is better lubricated and wear is unusual.

 

[DanH]

Pretty good info here:

https://tempestplus.com/wp-content/uploads/2019/01/Alaska-Cold-Starts-0613.pdf