central home oil heater, pump cavitating, what to do?

[paulmars]

I had to move the tank 3 feet further down towards ground. So, now the heater pump needs to pull fuel up 3 more feet. There was already a long distance from tank to pump. About 40 feet. The tank was at the same height as the pump. fuel got pulled up about 5 feet, over about 30, then down about 5 feet. Its been working like this for 26 years. However, I had to move tank down 3 feet. So, its now pulling up 8 feet, then over 30 feet, then down 5 feet. However, now it keeps cavitating. What to do? Last resort is to move the tank back up. Someone said a small low pressure automotive fuel pump mounted at the tank to push the fuel. This work?

tx,
pa

[HayZee518]

pump

if you are pumping fuel oil, then maybe a high lift pump, like the ones they use for a toyotomi laser heater might work. they're made to pump up over twenty feet.

[dfitz3390]

pa,
are you referring to a oil fired house furnace ?
when you refer to cavitating, do you mean your fuel pump loses prime and stops working ?
if the above is correct, do you have a brand, burner model or fuel pump model and one or two pipe fuel delivery from the tank to the fuel pump? top or bottom feed from tank ? or am i just misunderstanding everything here ?

[HayZee518]

pump

pump cavitation is the forming of air bubbles around the impeller volute. the volute is the exit from a pump. normally a pump, gear or a centrifugal is made so that cavitation is held to a minimum. but sealing surfaces are seldom airtight, even machined surfaces tend to wear admitting air and form bubbles.
oil burner pumps have definite specifications but they are mass produced on an assembly line so I doubt particular attention is given to each and every pump that leaves the factory.
I would look towards another pump for the burner.

[dfitz3390]

i think in this case, if my assumption is correct, the cavitation would be caused by a possible leak or too much vacuum created by the pump pulling the fuel the extra vertical length. fuel will break up and vaporize under vacuum at aprox. 6.7" .
most single pipe oil pump manufactures want the pump under 6"
if i remember correctly its .75-1'' per vertical foot of rise and 1'' hg per 10' horizontal run and about a half inch for a clean fuel filter. if you do the calculation you may be exceeding total rise to run . You may have been on the edge with the tank at its old height and adding the extra rise is too much vacuum for the fuel. With 8 feet v.rise you exceed the 1" per foot by itself.

[HayZee518]

fuel pump

if I'm not mistaken, most fuel lines use soft drawn 3/8" copper tubing from the tank to the oil burner. I've seen an AO Smith single pipe in most installations, but a two pipe [return] is not uncommon.
Factoring in what DFITZ said about rise and run, it may be necessary to run a larger inside dimension line, again soft drawn copper, to the pump and THEN reduce its size to the pump inlet.
given the length, I see 1/2-3/4 inch tubing then reduced to 3/8" - the return will probably be 3/8" because there isn't much pressure in the return line.

[dfitz3390]

i was hoping to hear back from Paulmars before we get too far into our theories about what might be, should be or could be the problem. maybe paulmars froze to death .

[Jim-Martin]

I need more info

To properly answer your question please answer the following:

1. Size of pump?

2. Horsepower of the motor?

3. Piping size?

4. What kind of fuel? Need to know the weight?

All of this information is important when talking about pumps.

There are Pump curves and formulas that need factors inputted for a correct answer


By the way,

It could be something as simple as air in the line