filter question

Lubrication System (oil feed pump and scavenger pump, reservoir, filter, and lines)
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Panshovevo
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filter question

#1

Post by Panshovevo »

This question arose in my mind after seeing a for sale post by one of the members.
If an oil filter has a bypass rating of xx psi, does it bypass at xx psia, psid, or psig?

I believe that when a filter is in a pressure feed situation, as commonly used in car and truck engines, it's psid, so I guess that on a Harley,(not sure about the twinkies) where the filter is in the scavenge/return system, it must be psig.
Any thoughts?

(Don't mind me, I got woken at 4:20 this morning after two hours or less of sleep. I'm back in PA, supporting my sickly brother again)

Regards,
John

PS MANY thanks to all who provide, support, and contribute to this forum, it's a big help at times like this.
john HD
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Re: filter question

#2

Post by john HD »

john

been up most of the evening, now morning due to a call at the power company.

don't quite understand the abbreviations you are using. up here in the frozen tundra the reason for a bypass on any filter is for 2 reasons. 1, if the filter plugs you need to still provide oil even if it is not filtered.
2 when it is way below zero and you start your engine with oil that resembles grease there is no way it will filter until the oil warms up. again, unfiltered oil is better than no oil.

if the filter is in the feed or return line makes little difference. even the factory harley filter has a spring and ball bypass built in.

john
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Re: filter question

#3

Post by Panshovevo »

psia: pounds per square inch absolute-does not include atmospheric pressure,which is 14.7 psi, or 29.92" of mercury at sea level in standard day conditions.
psig: " " gauge- calibrated to read 0 at standard atmospheric pressure
psid: " " delta, or differential, as in pressure drop across a restriction

After a cup of coffee, I think it must be psid in either situation, whether in a feed or return situation.

BTW, anyone know whether the filter on a twinkie is in the feed or scavenge system?
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Re: filter question

#4

Post by Cotten »

Johns!

Any restriction of the feed to the pump is highly undesireable.

....Cotten
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Re: filter question

#5

Post by Panshovevo »

Cotten wrote:Johns!

Any restriction of the feed to the pump is highly undesireable.

....Cotten
When I said feed, in this situation, I was referring to between the pump and the engine, as all in automotive systems I'm aware of, not between the oil tank and pump.
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Re: filter question

#6

Post by Cotten »

Panshovevo wrote:When I said feed, in this situation, I was referring to between the pump and the engine, as all in automotive systems I'm aware of, not between the oil tank and pump.
John!

I was just fearful.
If you can squeeze one in there on your Harley, Go For It!

...Cotten
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Re: filter question

#7

Post by BCOWANWHEELS »

BEST TO PUT A FILTER ON THE RETURN LINE..
Panshovevo
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Re: filter question

#8

Post by Panshovevo »

Guys, this was a theoretical question....
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Re: filter question

#9

Post by Panhead Ed »

wow ! I thought I was trippin
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Re: filter question

#10

Post by john HD »

i'm still awake and agree with cotten!

john
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Re: filter question

#11

Post by Panshovevo »

Panhead Ed wrote:wow ! I thought I was trippin
It made perfect sense to me, but obviously confused everyone else.
Let's say a filter has a bypass rating of 20 psi (pounds per square inch)
Does the bypass valve open every time the pressure upstream of the valve rises to 20 psi?
Or does it only open when there is a 20 psi difference between upstream and downstream of the valve?
Yes, I realize that there shouldn't be any significant pressure downstream of the filter on the Harley systems I am familiar with, but in other types of systems, babbit bearing engines and such, normal operating pressure is generally a good bit higher than that.

Maybe they just use a filter with a much higher bypass rating... anyone know?

I'd still like to know if the redesigned twinkie oil system filters the oil before or after the engine. This would help me figure out whether the twinkie filters can safely be used on earlier engines. I've been told they can be used, but don't know if they just fit, or are actually safe to use.

This is where my sleep-deprived mind started wandering yesterday morning when I posted the question. Hope this makes a little more sense than before.

Regards,
John
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Re: filter question

#12

Post by BCOWANWHEELS »

THEY BYPASS SOME OIL WHEN THE PRESSURE IS GREATER THAN THE BYPASS PSI. USEUALLY WHEN OIL IS COLD AND THICK. MY PAN IS 6PSI HOT. HOPE THIS HELPS
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Re: filter question

#13

Post by john HD »

i would say both.

some through the filter, some through the bypass until the oil warmed up enough. parallel circuit, the one with the least resistance gets the most.

plugged filter would be all through the bypass.

did get some sleep....

john
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Re: filter question

#14

Post by Frankenstein »

As I understand it, the filter on the Twinkie is after the feed pump, before the engine. Also, rumor has it that these filters have very small "holes", or however you rate filtration particle size. When I put the sporty pumps on my flatheads, I put the filter between feed pump and engine. Best place to have clean oil is going to the engine, I figure.
DD
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Re: filter question

#15

Post by Panshovevo »

Don't quote me on these numbers, but if I remember correctly, a Harley filter for earlier engines will filter particles down to 20 microns, but the TC filter traps down to 5 microns.
I wonder if they use a different bypass spring rate?

Regards,
John
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