Bubbles in the fuel...

Dirk_4

Hello, I converted a two pipe fuel system for an oil fired furnace to a single pipe with a tiger loop, but I'm having problems with the pump loosing it's prime and what looks like excessive bubbles in the tiger loop housing. The pipe size is 3/8" (10 mm ID) copper, and I see from the tiger loop literature that this is too large for such a low flow of 0.75 gph (2.8 kg/hr). They recommend 4 or 5 mm tubing instead, but I see that 1/4" is close at 6 mm. There is a warning in the tiger loop literature that converting from a 2 pipe system to a 1 pipe tiger loop system has the problem of too large of a supply pipe. They say that the larger supply pipe will cause siphoning problems and bubbles. Has anyone else done this conversion and replaced their line with smaller diameter tubing? I have a check valve in the supply line (mounted horizontally of course) but I still get a lot of bubbles and there are no leaks. I manually pulled fuel through the supply line with a special hand pump but got a lot of air bubbles no matter how much fuel I pulled through it. The installation is about 40 years old. I pushed fuel through the line as well, and when I pulled it back out, there was some nasty black liquid coming out. When the burner turns on, there is a lot of air in the lines and it burbs and flames out, but usually recovers and runs. Sometimes it times out though and trips the red button on the controller. The burner is a Beckett AFG. I found fuel puddling under the burner a couple of times, so I have a new pump to install, but don't know if that is the source of my problem with reliable burner operation. Has anyone replaced the line, or done something else, and eliminated all bubbles from the tiger loop? Sometimes there's a head of foam on the fuel that looks like some kind of red beer. The tiger loop is mounted above the pump, the tank is in the ground, the burner is in the basement, and the fuel line runs up in the ceiling and back down to the burner. I do not know if the tank is above or below the burner, in other words. Any help is appreciated.

I should add that the vacuum gauge on the filter housing reads at less than 5" Hg. It's a spin on type and the needle is the in the green zone.

Oh, and I installed a Delevan check valve in the nozzle, set to 100 psi. If the pump is running cleanly without bubbles, the pressure is set to about 105 psi. So, if there are bubbles in the pump (which is easy to hear), then the pump doesn't achieve full pressure and the nozzle shuts off the fuel. This is a good thing in my opinion, but I need it to run without very many bubbles to work properly.

Measured efficiency of the furnace is 82%.

scrook_2

Sounds like...

a small fuel line leak. 3/8" OD copper is standard oil line size even at 0.75 GPH. You may have a leaking joint or, worse, a pinhole in the copper. On pushing fuel thru you may have washed away black crud plugging the pinhole making leak worse.

Bob Bona_4

agreed

The vacuum reading is tainted by air laden fuel. Check all flares closely for suction leaks, look for kinks, if all LOOKS good, pressure test the line as far back as you can.

Erich_3

Fuel Line

Is your fuel line new? If not use a high quality fuel line made for oil usage. Make sure you use a long flare nut as opposed to a short flare nut. Debur the inside of the tubing prior to flaring it. I picked up a roll of Oil Pro-Tec tubing recently and it was very high quality and made in Canada.

A.J.

Tiger Loop

We did two Tiger loops this month, both were two pipe 3/8 " O.D. oil line on under ground tanks. One still has air coming in but the Tiger Loop is at least able to keep the burner on. We never had a problem with them draining back though it sounds like a pretty good size leak.

Dirk_4

Thanks

I will carefully inspect as much of the old line as I can to check for pinhole leaks. The hand pump I have has a vacuum gauge on it, and with the valve shut off, I pulled a vacuum where the copper line goes into the inlet to the pump. It seemed to hold it at 15 in Hg pretty good. I suspect the pump, which is 16 yrs old. The order of components are as follows:
tank->line->shutoff valve->check valve->firomatic valve->tigerloop/filter combi->vac gauge/pump loop.

Dirk_4

old fuel line

No, the fuel line from the tank to the shutoff valve is 40 yrs old. I hope that is not the problem because it is difficult to replace.

Dirk_4

small leak

We did have a small leak at one flare fitting. It was weeping ever so slightly. I cut a new flare and it seems fine now, but we still have lots of bubbles.

Dirk_4

pump leak

Well, while I was working on it, I noticed a small puddle of fuel under the burner. I believe the pump is leaking, so if replacing the pump does not fix this problem, I will be back here begging for suggestions.

Thanks everyone for your replies.

Dirk_4

tubing

I never heard of this tubing. We just use ordinary soft copper tubing. I did not debur the end of the tubing before flaring it. It didn't seem necessary with my high quality flaring tool. The flares it makes seem to me to be really nice. I will try that in the future though, thanks for the suggestion.

(yes, I used a proper pipe sealant on all threaded pipe fittings... no teflon tape! )

Edward A. (Ed) Carey_3

Oil line air (or future oil) leak

You should always debur any tube before flaring. Regardless of how good your flare tool is. The bur will compress under the wedge of even the very best flare tool and cause a high spot that can turn into a leak.

Also, I hope you didn't use any pipe dope on the threads or flare surfaces of the flares.

Flare fittings are not to have any sealant on the threads and especially not on the flare surfaces.

Flare connections are a machined surface to surface seal compressed by the tightening of the flare nut.

A good looking and well intentioned flare on a new oil line, can cause problems. Don't overlook them.

Also, if there is an oil line underground, with a suction leak, (ultimately a hole in the line) it is an oil release waiting to happen.

Even if you can get it to work now, you should plan on replacing a known and defective ungeround oil line ASAP.

Good luck,

Ed Carey

Dirk_4

proper flares

No, of course I did not use any sealant on flare fittings!

Thanks for your suggestions!

Dirk_4

From Tigerholm

Here is what the manufacturer says about pipe sizes:

"When calculating the appropriate suction pipe dimension, pipe resistance and suction height must be taken into consideration. Different pipe dimensions allow different lengths of suction pipe. The tables below are only a recommendation, which show basic guidelines using theoretic values. Too low velocity will lead to air/gas separation from the oil resulting in large amounts of air/gas travelling to the pump causing noise and eventually flame failure.
Using a suction pipe with an oversized inner diameter will result in a loss of the siphon effect in the descending parts of the suction pipe. If an oversized inner diameter is unavoidable, all ascending parts of the suction pipe must be calculated as suction height instead of simply figuring the height from the lowest level in the oil tank to the oil pump. Remember that suction height must not exceed 4 meter, as this will lead to noise and unnecessary wear and tear on the pump.
The siphon effect must be calculated using the lowest potential flow in the suction pipe. For example, when using an oil burner with multiple effect stages, the lowest stage should be used to calculate siphon effect. The maximum effect stage should be used to calculate the pipe resistance.
When calculating the appropriate suction pipe dimension, siphon effect should be taken into consideration. The figures below show siphon effect at different flow velocities.
Inner diameter Siphon effect starts at:

4 mm a flow > 1,6 kg/h
6 mm a flow > 5,5 kg/h
8 mm a flow > 20 kg/h
10 mm a flow > 35 kg/h"

For 0.75 gph (2.84 kg/hr), we should be using a 4 mm tube, which is really tiny. Quarter inch tubing is about 6 mm, for example.

The also state:

"When converting from a two-pipe system
to a one-pipe system it is important to
consider the dimension of the suction
pipe (feed line). The suction pipe in a
two-pipe system is often too coarse as
the oil flow in a two-pipe system is up to
20 times higher than a one-pipe system.
Too coarse of pipe in a one-pipe system will
lead to gas bubbles as siphon effect is lost
in any descending sections of the suction line.
For calculating the correct dimension suction
line and other details for the optimal installation,
please refer to your local distributor.
Information is also provided on our website at
www.tigerholm.com."

Big Ed_4

Flair 101

You should cut, file off the concaved section and then deburr for a good flair.

Erich_3

Oil Pro-Tec Fuel Line

Dirk, I get my Oil Pro-Tec fuel oil line at Sid Harvey. It comes in 50 ft, 100 ft and 250 ft rolls. It has an orange polyethylene covering. This brand of tubing is specifically made for fuel oil. It is made by Kamco which is a subsidiary of Granby. The company also makes tubing for natural gas and LPG called Gas-Tec. They also make Aqua-Shield which is a coated tubing for water. Here is their website.

http://www.kamcoproducts.com/index.asp?content_id=1

Dirk_4

wow...

OK, did not know that I should file *and* debur... wow. Thanks.

Dirk_4

thanks!

I'll check out that fuel line. Is the plastic sheathing for protection?

steve_29

Dirk , get rid of the check valve, you don't need it, it only serves as an additional restriction to the oil line.

Sounds like your oil line is restricted and needs replacing.
I would replace as much of the line as I could.

Dirk_4

check valve

Thanks for the suggestion. The check valve doesn't seem to make much difference after installing it, so maybe you're right. I installed it because Tigerholm required it.

When I pulled fuel through the line manually, it was really difficult. There would be a delay between developing suction and when the fuel would begin flowing. This even occured when I was pulling as far up the line as I could get, which is before the shut off valve. Replacing this line is going to be a pain...

Dirk_4

another idea...

How about this?

tank->line->shutoff valve->filter->shutoff valve->Toyotomi lifter pump (with builtin outlet shutoff valve)->OSV->single line to pump.

In other words, get rid of the tigerloop entirely and install the lifter pump a few feet above the pump to provide some gravity positive pressure to the pump's single line. The lifter pump can handle up to 4 gph, so that's not a problem. It holds over a quart of fuel.

Crazy, I know... but...

steve_29

I can't find where Tigerholm requires it.

The dearator is working as it should, removing air from the fuel.

I suspect that a back pump seal was your undoing, but a restricted line may have been the reason the seal failed.

I would suggest replacing the underground tank with possibly a Roth style and repiping the entire system.

After 40 years, I would guess your tank is on borrowed time.

Dirk_4

I agree

I think at least a thorough inspection of the tank and related equipment is warranted. Thanks for your help.

Oh, they call for an anti-siphon valve near the tank. It's basically a check valve.

Erich_3

Oil Pro-Tec Benefits

The coating protects the copper from corrosion and it also has grooves so that in the event of an oil leak the oil will migrate to the end of the tube and it will be obvious that there is an oil leak. The orange colored coating makes it easy to identify the location of the oil line and also identify that it is an oil line. It is also available in a version with an outer sleeve.