Cooler line pressure drop

[Killerbees]

Where can I find data on pressure drops for AN-10, 12, 16 line? Would seem to me that it is vital to sizing various applications.

Example, at 10 gpm, I can calculate that oil will flow at 10 ft/sec in an an-12 line. But what is the pressure drop over 5 feet of line?

 

[Killerbees]

Hmmm. Is it possible that there is a forum that specializes in all aspects of lubrication and oil transport, but no information to discuss oil flow challenges?

How do you guys make a decision on the size of an oil line? Just guess?

 

[Gary Allan]

I doubt that you'll be able to measure the pressure drop in anything other then inches of water column over a 5 ft span.

The more important figure is what pressure you develop at the pump in terms of back pressure. If you don't reach the pressure relief of the oil pump, then it doesn't matter if you use capillary tubing ..the oil will just increase in velocity to pump the 10 gallons a minute.

Let me say that another way. The larger the gap between your peak oil pressure (the pump limits) and your typical operating pressure ..the more tolerant or less sensitive to line size the system will be.

I think #8 would work for just about anything. Others like to feel more assured with #10 or #12.

 

[Killerbees]

The diesel flows 20 gpm. Will be considerably more than inches of water.

20 cP, 62 lb/ft^3, the long math on velocity is 20 ft/s in AN-12. That's a very large (psi) drop over 5 ft. Several psi, like 30 psi, in an AN-8 line.

I guess I just need to do it longhand.

 

[Gary Allan]

Well, it isn't a drop. You don't lose anything ..nada ..zip ...ZERO unless you bump the pressure relief of the oil pump.


I can't integrate your math (not surpising)

 

[Killerbees]

"Let me say that another way. The larger the gap between your peak oil pressure (the pump limits) and your typical operating pressure ..the more tolerant or less sensitive to line size the system will be."

Yes, exactly. In our case, pump relief is set to 80 psi. System pressure typically runs 50-60. So I have roughly 20 psi I can add. Doing so at the peril of oil pump lifespan, if I understand constant displacement pumps. Better to plan for minimal added plumbing stress.

But I'm no expert, I have a lot to learn. Thanks for providing this site.

 

[michael harris]

Why would you have that sort of pressure drop in only 5 foot of straight tubing..? you lose flow at any bend or drastic change of direction, but if the line is not flexing under pressure, which there's no reason it should be to any sizeable amount, then other than minimal friction losses your output should be relatively close at the end of 5 feet as it is at pump outlet. I know on my dry sump it has 1) -10 supply or pressure line that is in excess of 100 on initial fire and when hot is around 85-90 at w.o.t. maybe the earls site has figures for losses in lines , what kind of line is this application..?
44H

 

[Killerbees]

"Well, it isn't a drop. You don't lose anything ..nada ..zip ...ZERO unless you bump the pressure relief of the oil pump."

Point taken.

 

[Killerbees]

"I know on my dry sump it has 1) -10 supply or pressure line that is in excess of 100 on initial fire and when hot is around 85-90 at w.o.t. "

Do you know how much of that, is due to the added line? It is significant

 

[Gary Allan]

I don't lose anything over about 72" with #8 @ approx 10gpm. That should be very close to your #12 @ 20 gpm.

I don't lose anything with #6 either ..but I don't have the gpm figures to index it

50% increase in cross section yields 225% in area.

 

[Killerbees]

"I don't lose anything over about 72" with #8 @ approx 10gpm. That should be very close to your #12 @ 20 gpm."

Gary, Are you saying you don't have a pressure drop, running lube oil through a 1/2" diameter opening, at over 25 ft/s velocity?

Just trying to be sure I understand

???

 

[Gary Allan]

What I'm saying is that I installed 72" of #8 line to a remote mount and saw no difference in downstream pressure ..with a 10 gpm rated oil pump (High Volume).

The velocity, if I reasoned it correctly, should be the close to your 20 gpm in a #12 line. Your #12 line has 225% of the cross section ..your flow is 200% of my 10 gpm.

I'm sure there are factors of the physical mass of oil and friction losses ..but on a practical model that I've observed ..and looking at it "statically" (as in suspend ancillary factors) ..I don't think that you can run into substantial issues over that span with that size line

 

[Killerbees]

If you have established 10 gpm through that line, you are at 15 ft/s, and 10 psi pressure loss from friction, on a 6 foot length. Fittings add to that!

With cold oil, it is 20 to 50 psi!

All assuming .5" id.

As for the "downstream pressure" statement. No it won't change, assuming flow is the same. All it is reflecting is the pressure losses "downstream" of the gauge, correct? Put the gauge on the upstream end of the line, before and after, and there will be a 10 psi difference. The gauge has no idea what happened up river.

Back to the stock vehicle. Assume it has 60 psi on the gauge. Is that pressure created by the pump? No. Is it created by (plumbing) resistance to flow that the pump is providing? Yes. Further, it is resistance to all flow, happening downstream of the measurement site. The pressure reading will be 60 near the pump outlet, and 0 near the plumbing outlet. At all points in-between, the reading will be between 0 and 60, the closer to the outlet, the closer to 0 we get. And without flow, all readings will be 0.

I think you have grossly misjudged pressure drop in oil lines. A 911 has -16 oil lines as a minumum requirement for oil coolers, for the reasons I have stated. I think they flow around 15-20 gpm with a dry sump if I'm not mistaken, some 10-12 qts of oil. If the pump on the porsche used -8, it would run into 70 psi on the cooler line alone. IOW, very early pressure relief at the pump.

 

[glennc]

Killerbees, I'm quite sure you're right. Another way to think of it is that between the oil pump and the return to the sump the oil pressure has dropped from full to zero as it has moved through all the engine's oil passageways and oil lines. Adding several feet of line will make a significant difference to either the pressure, the flow, or both, and what effect it will have would depend a lot on the design of the pump and its relief valve.

If the pump is already bumping up against its relief setting in normal use (worst case), then it will translate into a loss of flow, and while the pressure of the pump output would remain the same, the pressure inside the engine (assuming engine is downstream of oil cooler) would be reduced. Less flow at lower pressure sounds like a bad idea. So, I agree, it is important to try to find out. Have you tried googling the subject to see if there are any general formulas that relate pressure drop to fluid viscosity?

- Glenn

 

[Gary Allan]

quote:

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As for the "downstream pressure" statement. No it won't change, assuming flow is the same. All it is reflecting is the pressure losses "downstream" of the gauge, correct? Put the gauge on the upstream end of the line, before and after, and there will be a 10 psi difference. The gauge has no idea what happened up river.

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I totally agree. I will requalify my statements to include that I have read at the egress from the engine and the return and have seen no significant differences with this as an intermediate addition. I saw little if any difference with my volumes pumped through #8 line. I don't have my current setup configured to measure that way ..but I wouldn't expect it to be much different with #6 (however, I admittedly don't know the volume).

The biggest factor that I noticed was pump head ..even that appeared marginal.

I wish XS650 or 427ZO6 were here (they're on holiday from BITOG) they could whizbang your numbers a little.

 

[Killerbees]

"Have you tried googling the subject to see if there are any general formulas that relate pressure drop to fluid viscosity?"

The equations are derived from Chemical Engineering text. I shall try to find an on-line calculator.

I do have some data from Setrab I had to dig up, but relate to connections only, don't think the lines are included. -10 fittings to the cooler add 10 psi at 20 gpm. -12 would add 5 psi. Let me see if I can post some links

 

[Killerbees]

Good one Gary. Here is one also.

http://www.processassociates.com/process/fluid/dp_1.htm

Density is 62 lb/ft^3
visc is 15 Cp hot, 150 Cp cold

 

[Killerbees]

I think the reality for many folks is less GPM than was previously thought. If using -8 lines expecting 10 gpm, there is a surprise in there.

 

[Killerbees]

Forgot to mention, -8 is .42 id
-10 is .5" id
-12 is .64
-16 is .88

Aeroquip FC807 teflon, SS braid.

 

[Gary Allan]

quote:

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Aeroquip FC807 teflon, SS braid.

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I was wrong

They will cost $200.

Just curious here. Why the top shelf hardware when it can be done cheaper with not too much difference in reliability or performance when compared to properly rated hydraulic line?