SmokinBBC
Well-known member
What oil pressure triggers the relief valve in the filter adapter? '70 BB if that makes a difference.
Filter pressure relief valve
- Thread starter SmokinBBC
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mrvette
Phantom of the Opera
I have NO clue....guess at 80 psi.....
but I have heard comments that a typical engine can float a bearing at as little as 20 psi, and that's at 6000+ rpm.....I forget the exact quotes, but i'ts not much pressure....which surprised hell outta ME....
:clobbered:
but I have heard comments that a typical engine can float a bearing at as little as 20 psi, and that's at 6000+ rpm.....I forget the exact quotes, but i'ts not much pressure....which surprised hell outta ME....
:clobbered:
SmokinBBC
Well-known member
So at pressure above 12-15psi all the oil passes through the filter? So the only way to trigger the valve is with a clogged filter?
I am reading fishers book on hotrodding BB and came across the valve in the lubrication section. I doesn't explain the function of the valve very well.
JPhil
Huh?
No, at 15 PSI the bypass valve opens and allows oil to bypass the filter. Some oil still circulates through it, but some just recirculates through the engine without going through the filter. If the filter becomes blocked, all oil will bypass it allowing the engine to still have pressurized circulation.
SmokinBBC
Well-known member
Ok. Since most engines...at least my vettes.....always had pressure well above 15psi, then what good is a valve? Basically, it is always open.
Fisher recommends blocking the valve so that the oil always flows through the filter. Wouldn't it make more sense for the valve to open at higher pressure, say 60+ psi with a filter that can handle the pressure? Perhaps they were more concerned about filter blowout back then.
Fisher recommends blocking the valve so that the oil always flows through the filter. Wouldn't it make more sense for the valve to open at higher pressure, say 60+ psi with a filter that can handle the pressure? Perhaps they were more concerned about filter blowout back then.
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JPhil
Huh?
Jeez, I retract my above statement---I think I have it backwards!!
Up until the filter bypass opens, all the oil circulates through the engine. When the bypass does open at the set pressure, assuring that the engine has enough oil pressure for it's lubrication needs, then some of the oil goes through the filter. Either way, the oil filter is on a side loop, not in line, on a Chevy engine so not all the oil goes through it all the time. And if the filter becomes plugged, the engine still gets full lubrication
Man, I'm sorry--- Now I've gone & confused myself as well. I should just shut the fuck up and let someone who really knows answer.
I learned this on an old Chevy truck 6-cylinder. It had the big ol' canister filter, with rubber lines from the block. The oil filter was basically an accessory. It had a small orifice to restrict flow and keep the block pressured up. I replaced it with a spin-on filter adapter and my oil pressure dropped to about 2 PSI at idle. The oil was short circuiting through the filter because it had less resistance than through the oil passages of the engine. I found a pressure valve I could put in the filter feed line which opened at about 15 PSI and all was OK. As far as I have known, the V8 blocks have the same set-up. But fuckin-A I could be wrong. Now I want to know too.
Up until the filter bypass opens, all the oil circulates through the engine. When the bypass does open at the set pressure, assuring that the engine has enough oil pressure for it's lubrication needs, then some of the oil goes through the filter. Either way, the oil filter is on a side loop, not in line, on a Chevy engine so not all the oil goes through it all the time. And if the filter becomes plugged, the engine still gets full lubrication
Man, I'm sorry--- Now I've gone & confused myself as well. I should just shut the fuck up and let someone who really knows answer.
I learned this on an old Chevy truck 6-cylinder. It had the big ol' canister filter, with rubber lines from the block. The oil filter was basically an accessory. It had a small orifice to restrict flow and keep the block pressured up. I replaced it with a spin-on filter adapter and my oil pressure dropped to about 2 PSI at idle. The oil was short circuiting through the filter because it had less resistance than through the oil passages of the engine. I found a pressure valve I could put in the filter feed line which opened at about 15 PSI and all was OK. As far as I have known, the V8 blocks have the same set-up. But fuckin-A I could be wrong. Now I want to know too.
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MYBAD79
Moderator
Well, here are a few photos (a pic says more than 1000 words)....
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When the bypass valve opens it allows oil to bypass the filter. Here's the adapter without the bypass:
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I would hope it doesn't open until the pressure is up to 60psi, otherwise it would be open all the time and the oil doesn't get filtered....
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When the bypass valve opens it allows oil to bypass the filter. Here's the adapter without the bypass:
.
I would hope it doesn't open until the pressure is up to 60psi, otherwise it would be open all the time and the oil doesn't get filtered....
Twin_Turbo
Der Maulwurf
- Joined
- Mar 5, 2008
- Messages
- 7,579
You have to realize that it's not the system pressure of 15psi that opens it but a pressure DIFFERENTIAL of that over the filter. Basically a pressure drop due to cold/thick oil, a clogged up filter......
Everything is relative so even with a 15psi spring setting on the relieve valve, it only opens when one side has 15 psi less than the other side, whether this is 30 vs 15psi, 50 vs 35, 80 vs 65...blah blah blah...doesn't matter.
The oil filter is NOT on a side loop, it only is if you forget the hidden plug in the rear vertical passage. The oil filter adapter only bypasses to keep the filter from bursting. I have always replaced the spin on adapters with non bypassing ones and used either large case filters or a System 1 mesh filter. Never had a problem. Especially with the System 1 filter it takes a ton of pressure to burst that thing. So, if you have a pressure drop of more than 12-15psi over the filter, that's when the bypass opens.
The bypass valve in the PUMP is what bypasses the oil back to the sump to regulate max. system pressure. If that one opens the oil gets routed back into the sump via the relief port.
Everything is relative so even with a 15psi spring setting on the relieve valve, it only opens when one side has 15 psi less than the other side, whether this is 30 vs 15psi, 50 vs 35, 80 vs 65...blah blah blah...doesn't matter.
The oil filter is NOT on a side loop, it only is if you forget the hidden plug in the rear vertical passage. The oil filter adapter only bypasses to keep the filter from bursting. I have always replaced the spin on adapters with non bypassing ones and used either large case filters or a System 1 mesh filter. Never had a problem. Especially with the System 1 filter it takes a ton of pressure to burst that thing. So, if you have a pressure drop of more than 12-15psi over the filter, that's when the bypass opens.
The bypass valve in the PUMP is what bypasses the oil back to the sump to regulate max. system pressure. If that one opens the oil gets routed back into the sump via the relief port.
Unless you use an accumulator with a bypass system, oil always bypasses the filter at startup and often when revved cold.
If worried you can space the spring a little with washers or install a heavier spring. Even the cheap filters have a case burst pressure of at least 200 psi but they can balloon or burst.
You can also change just the filter and add a quart more often. A cheap fix.
The early cannister type filters offer almost 100% filtration but the adapter has to be changed for that type.
If worried you can space the spring a little with washers or install a heavier spring. Even the cheap filters have a case burst pressure of at least 200 psi but they can balloon or burst.
You can also change just the filter and add a quart more often. A cheap fix.
The early cannister type filters offer almost 100% filtration but the adapter has to be changed for that type.
SmokinBBC
Well-known member
Ok. Now it makes sense.
I had misunderstood the purpose of the valve. I had initially thought along the lines that Gene and Karsten were going and was concerned that the filter was being bypassed alot. At operating temp, I have 35psi at idle and 70psi at cruise and a little higher at WOT.
I had misunderstood the purpose of the valve. I had initially thought along the lines that Gene and Karsten were going and was concerned that the filter was being bypassed alot. At operating temp, I have 35psi at idle and 70psi at cruise and a little higher at WOT.
JPhil
Huh?
:footmouth: :clobbered: :suicide: :gurney:
:thumbs:
:thumbs:
MYBAD79
Moderator
Would be nice to know what the actual pressure delta across the filter is (cold oil, hot oil)... I am on the fence right now but I think I'm going to install the 'no bypass' adapter... if you buy good filters and change the oil every 3000-5000 miles you should not need the bypass... maybe in cold climates when you start the engine at 0F and the oil is thick like jelly.... :sweat:
SmokinBBC
Well-known member
I was thinking the same thing. But IF I am now on the right track, other than opening when the oil is cold/thick, there should be very few times when the bypass opens....possibly quick revving which would cause a higher differential pressure?
big2bird
Charter Member, Founder Bird-Run, Cruise-In Bird-R
My intuition states that GM installed it for a good reason. There is so much flow going on, I don't see the need to filter it 100% of the time. Specially if you change it every 3,000 miles.
Engines did not even have filters untill the late 30's, early 40's.
Then again, with the expensive metal mesh filters, and frequent oil changes, I can see some benefit with 100% filtration.
Engines did not even have filters untill the late 30's, early 40's.
Then again, with the expensive metal mesh filters, and frequent oil changes, I can see some benefit with 100% filtration.
SmokinBBC
Well-known member
Know that I am educated, it is staying the way it is for now. Thanks all:thumbs:
JPhil
Huh?
Me too......
pcf_mark
Well-known member
- Joined
- Aug 22, 2008
- Messages
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For a street car I would use the bypass. You never know when you need to fie it up and gun it on a cold day. It expands the oil filter casing (!). For a race car I would plug it (see GM power book) because you have a more controlled situation. If you run an oil cooler you need to plug it or oil will bypass the cooler.