Pressure/ vacuum in supply and return

seized123

Much of what I’ve read implies that leaks in return lines in two pipe systems are more of a danger than in supply lines. Is this true?

I’ve  been thinking about this, and is it correct to say that although there must be plenty of suction/vacuum/negative pressure in the supply line while the pump is running, this negative pressure might tend to keep the oil inside the pipe at a leak or hole, although perhaps it will also suck air in; but the positive pressure on the return might tend to push oil out a leak, hence an increased danger when there is a return line leak? Am I thinking about this right?

Then there’s the case, when the pump is not running, of oil siphoning out a leak when the bottom of the tank is well above the level of the burner as mine is. (Also in mine the lines come out the top of the tank.) In this case it seems to me that a hole at a level below the bottom of the tank presents an equal risk of siphoning in either supply or return (with pump off) with the qualification that if the return line inside the tank only goes a few inches down into the tank as I gather it should, it would only siphon oil until the oil level got below it. (In that way, a siphoning leak would maybe be worse on a supply line, hence anti-siphon valves or OSV’s on supplies?) Also correct?

Finally, moving on to a one pipe system, is the (negative) pressure from the pump in a one pipe only a fraction of what it is in a two pipe system, since most of the oil that goes through the pump is recirculated back to the pump right away, and only the amount actually used by the nozzle is replenished by the tank? If so, is this reduced risk of (non-siphoning) leaks in a one pipe system a main reason for recommending one pipe? (I know that filters quickly clogging is another.)

I’m to all this, so some principles which are second nature to you, I’m just learning.

EBEBRATT-Ed

I believe in two pipe systems and I think "the return line may leak" is overdone. But that is just my opinion.

Almost everyone here will disagree with me about that.

The one upside to a one pipe especially with an outdoor tank is that the oil moves slower (you only moving nozzle capacity) so it gives the oil a chance to warm up.

Then there is the Tiger Loop which most everyone besides me loves.

seized123

Interesting @EBEBRATT-Ed. Personally, after all I’ve read on this forum on the subject, I’m leaning away from your preference for two pipe systems, almost entirely because of the leak issue; but like you (though maybe for different reasons) I’m leaning away from the Tigerloop too.

I’ve seen the opinion expressed in some posts that Tigerloops are unnecessary for tank-above-burner (“gravity”?) setups as long as all flares and connections are good (though this opinion seems to be in the minority). In my mind I add to this that while the Tigerloop goes on a nominally one pipe system, between the Tigerloop and the pump it’s two pipe, with all that extra gph going around in circles; thus if there were a leak between TL and pump, it would be worse than one pipe no TL. Add to that that braided lines are often used there - and from a recently closed thread I’ve come to distrust braided lines, at least the kind under sinks, but I guess one could go with copper between TL and pump.

I may be overthinking the leak factor, which is frankly driving all my thinking about the system lately, I’ve just been struck with the idea that one serious leak could wipe out one’s savings, so might as well optimize to reduce all chances.