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Oil heat: Highest recommended oil supply line vacuum reading

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D107
D107 Member Posts: 1,852
Looked at the family's heating system today; getting near annual tuneup. Vac reading with burner firing reaches 9 or more the highest I've ever seen it. Usually maxes out at six or seven, especially when tank is low. The oil company let the oil level get very low a few months ago, I'm thinking maybe some sludge in the line. Also last year the intake hose came off and after they installed a copper pickup they had to leave the old one in the tank. I'm wondering if a blockage from the old hose is possible--seems that if the bottom of the copper intake was at least three or four inches that wouldn't be likely but I'll see what you guys think. When they pull the 50 and 10 micron filters to replace them, if they're both fairly clean then it would seem it could be the old hose. The use Biofuel 20, and generally the vac readings had been lower for most of the year. Hope they're giving me good oil. This is a ten year old Roth tank.

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  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    2 pipe? Even at 7" you're at the upper limits of a one stage pump. What burner?
    Paul S_3D107
  • D107
    D107 Member Posts: 1,852
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    Riello 40 F3. I believe this is one-pipe with a Tiger Loop. If vac gets too high burner will shut off? I'll get the company in there Monday or even tomorrow.
  • D107
    D107 Member Posts: 1,852
    edited March 2017
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    Most of the gauge photos show 8 as upper limit of green area, from 8-15 as yellow, and red from 15 on. But don't know if that's for single or dual lines.


  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,616
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    It's for any system. If the vacuum gets to high the oil starts to foam and then it acts like air in the system.

    In the old days 15" vac was considered about the maximum. Now, the oil is different. I would prefer to keep it below 10" if possible. As @Bob Bona mentioned different pumps single stage versus two stage have different capabilities.

    single stage has 1 set of gears, two stage has 2
    Bob Bona_4D107
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    15-30 means there's serious flaws in the oil supply design :)
    D107
  • D107
    D107 Member Posts: 1,852
    edited March 2017
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    Thanks very much @Bob and @Ed for your replies. Since the usual burner-on vac reading on a full tank is 1-3 I think the design is ok, there must be some buildup or blockage somewhere. I forgot to mention that the tiger loop is over ten years old; the manufacturer recommends replacement after 8 years, though I don't know if a defective tiger loop could cause this issue. (The burner is only about 8-9 ft from the oil tank.)
    Bob Bona_4
  • HVACNUT
    HVACNUT Member Posts: 5,863
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    When the tank is full, you should be able to remove the gauge and pull out the old pick up line. Is the Roth valve still in place on top? With the tank so close, vacuum should be 0.
    D107
  • D107
    D107 Member Posts: 1,852
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    I had inquired on The Wall about removing old pickup line. The oil co. guys tried but couldn't do it. Apparently it lies on the bottom and doesn't float. There are some tools available for this kind of extraction but basically I was told to leave it there--one comment was that the inner lining of the Roth tank could be punctured by the fishing attempts. I'm attaching some photos of boiler setup, and old and new Roth connections. Looks like the new Roth connection could use some vertical support.


  • HVACNUT
    HVACNUT Member Posts: 5,863
    edited March 2017
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    That set up is fine at the tank. The tiger loop is not a cause because it's after the vacuum gauge.
    Try closing the firomatic valve at the spin on filter while the burner is running. Vacuum should not rise for a while, using the oil in the tiger loop.
    No kinks anywhere?
    My Roth is over 80' away with a Riello and Tiger Loop Ultra and it runs a 0 vacuum.
    Could be the old pick up tubing, which I always eliminated along with that valve, is being pulled toward the copper pick up.
    Call your oil company, put your account on delivery hold until further notice. Let the tank run low. Get 10' of #10 THHN wire, solid, bend a hook on one end, remove the tank gauge and pull out the old tubing.
    Resume deliveries.
    Bob Bona_4D107
  • D107
    D107 Member Posts: 1,852
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    Thanks. The manufacturer Roth's advice is similar to yours--could also use extended reach grabbers with rubber tips. They don't think damaging the interior is a risk for this kind of endeavor--the inner wall is 3/16 inch of high density polyethylene.
    Bob Bona_4
  • Big Ed_4
    Big Ed_4 Member Posts: 2,806
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    Your vac should be be at "0" ... Roth is an top feed tank and any top feed will breed sludge . Water + oil = environment for an algae . The algae eats the oil and **** out an sulfuric acidic sludge ..The tiger loop is a plus for air collecting in the top feed loop ... The fall should off set the rise if on the same plane .. If there is an vacuum , especially high you have blockage ..Pull the dip tube , there is all kinds of growth down there .. What I remember the drip was an hose with an weighted end ? That four section Buderus , with 150# is about 90 gph ?? one pipe

    There was an error rendering this rich post.

    Bob Bona_4D107
  • D107
    D107 Member Posts: 1,852
    edited March 2017
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    Thanks. This is a G-115/3 (21)...fires at 84K Btu/hr .60 gal. The old hose with weighted end was replaced last year with a copper line--see photos above in the thread. I had always been told that the Roth, being non-metallic inside would inhibit any bacteria, that the old style bottom feed steel tanks were the bacteria breeders, but I recognize everyone's experience is different under different conditions. Add Bio-Fuel 20 to the mix and that's supposed to keep the fuel cleaner, which seemed to be true until the oil company let the oil level get down to maybe 1/8 tank. The feedback on appropriate level of vacuum has also varied. Some say their burner is 80 feet from their tank and their Vac is 0. Others point to the distance, fittings, the two filters, the lift, and say that my vac reading of 3-5 is normal. There's even a formula out there to calculate vac:
    LxQ=?+H=V
    L = Total length of fuel line.
    Q = Fuel line diameter x GPH.
    H = Total lift from the bottom of the tank to the middle of the fuel unit. V = Vacuum hg. inches mercury. As an HO, I'm always educated by the debates and explanations from you folks who do this every day.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    1" per vertical foot, 1" every 10 foot horizontal was drummed into my head as expected Hg back the ICPA days 25 years ago
    D107CTOilHeat
  • D107
    D107 Member Posts: 1,852
    edited March 2017
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    Well just to follow up, we had the oil co tech out today. The General 50 micron at the thank was pretty gunked up; can't really tell about the 10 Micron spinon but as soon as they were replaced, burner-on Vac reading went from about 9 down to 0. Nozzle and pump filters were pristine. What's confusing to me as I try to understand the physics of this, is how does this '0' reading jibe with all the calcs of 1" per restriction of each filter, lift, distance, etc. I'm sure vac reading will rise a bit as time goes by as filters get used and oil level in tank falls, thereby increasing lift. Note that tank was half full today. Thanks for all your thoughts on this.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    Sounds good! Thanks for the followup. I write the before and after Hg and the filter change date on the spin on canister.
  • HVACNUT
    HVACNUT Member Posts: 5,863
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    I read your 1st post wrong. Thought you wrote filters were fairly clean.
    With a high vac, that's the first clue.