Pressurising an oil storage tank

[Cursitor Doom]

Why would he want to do that? I hear you ask.

Well, I find that when my 1200 litre capacity heating oil tank level drops to the last 8 inches or so, the boiler starts locking out. So I end up with several days of no heating until the fuel people can be arsed to come and deliver the 1000 litres I ordered about 10 days ago, which still hasn't shown up yet.

I'm thinking if I could increase the air pressure in the tank so it presses down on the residual oil with sufficient force to mimic the presence of a few hundred litres of oil, then I would get an extended lease of life on the remaining oil which would be forced into the boiler and I wouldn't have to sit around freezing for up to two weeks whilst the fuel people get their act together.

Could this be implemented with off-the-shelf plumbing fittings and what is the likelihood that such a concept would work? I already have a suitable air pump from an old jacuzzi that would probably generate sufficient puff. I could seal off the main filler hole making it air tight and fit a say 15mm diameter boss into the side wall of the tank close to the top in series with a one-way valve then piping to the air pump. What do you think?

[Tim+]

Or you could raise your tank by 8".

If your tank is already at the approved height it would probably be worth checking your pipework & filters for a partial blockage.

Tim

[curious]

A tiger loop does the job where the oil tank is below boiler height.

[Andy Burns]

Assuming there's 1.5m depth of oil when full, that's 2psi, sounds low right? But if you pressurise it there'd be 1000 litres of air at 2psi which is about 54kJ of stored energy in a tank designed to stop oil pissing out, rather than holding air in - think of a 180Ah car battery letting all its energy out at once.

Get a taller, narrower tank, so there's greater static pressure in the same volume of dregs?

[harryagain]

An extremely foolish idea that could lead to an explosion or the tank bursting. Just raise the tank. Obviously when it's empty.

[curious]

Or fit a tiger loop

[Nick]

Is the tank steel, plastic or otherwise? Is it bunded. What shape? circular or square edged? Frankly I think your proposed solution is a recipe for disaster. Especially if you are anywhere near a watercourse. Have you checked the filter(s) and bottom of the tank for gunge? Even with the best of attention every tank will accumulate some muck over time. Also that 8" reserve might just prevent your boiler from sucking in all the dregs and goosing the boiler pump. Don't think about pressurising. Cough up and buy fuel before push comes to shove. After checking the tank & filters of course. Nick.

[newshound]

Well yes, but you are only raising the stresses to the same level that they are in the bottom of a full tank. Now, if it was made of glass you could, in theory, release the energy in a dangerous way but only, I suspect, to someone standing fairly close. (I havn't checked the energy sums). If your pump can only generate a few psi I see little risk. (A garage air compressor would be a different matter).

That said, I think I would be checking pipework and filters first.

[Andy Burns]

But under pressure all surfaces will feel the effect, maybe the manufacturer produces tanks which are thicker at the bottom, and thinner at the top where normally the pressure would be expected to approach zero.

[Rick Hughes]

If you are sure filter & pipes OK .. but some blocks under tank raise it up, much easier than pressurising. Couple of 100mm conc blocks on flat ?

[Dave Liquorice]

Plastic oil tanks are rotational mouldings. That is "liquid plastic" is put into the mould that is then rotated coating the inside with a uniform layer of plastic.

I was also thinking that the pressure needed will be very low but hadn't taken into account the volume of air. Not done the energy calcs either but a plastic tank is not likely to suddenly let go.

I'd be looking for blocked filters, pipes etc first, All manner of crap seems to find it's way into an oil tank. Burner pumps do have a bit of suck, so if having to lift the oil against a partial bockage could suck air in. Oil being a larger molecule might not leak out...

If was frosty I'd also mention that water collects at low points and can freeze... DAMHIKT. Suffice to say there is now a glass bowl filter at the tank to catch water before it enters the pipework and is easy to inspect.

[Dave Liquorice]

Well ish, a tiger loop is really a de-aerator it's not a lift pump. B-)

Just looked at the destructions for our Rielo burner max vaccum is

0.4 bar (6 psi) in two pipe mode. To lift 8" of water is 0.28 psi, oil is less dense so will require a bit less. This isn't going to stress a burner pump, even in single pipe mode.

There must be another reason, blockage/severe restriction, air ingression, half triggered fire valve.

[Michael Chare]

It should be possible to get the specifications for the pump and see if the hight difference is within the correct range.

Most pumps will convert to a two pipe system which has a greater lift, though the tricky bit is returning the oil to the tank correctly.

[Fredxxx]

Frost, water and glass really don't mix! Are you sure its glass?

[Cursitor Doom]

There's already one fitted, same time as the boiler was last changed about 26 months ago.

[Cursitor Doom]

Er, I've already ordered the bleedin' fuel! It just refuses to turn up! OK, so pressurising the tank is not the way to go. I get that. Relax everyone; no explosions a-comin'.

[Michael Chare]

Yes, the OP just referred to the last 8" of oil in the tank. The oil level to pump height difference was not stated.

Failure to change paper oil filters can cause blockages.

The Danfoss instructions I have suggest a max lift of 2m for a 1 pipe system and 4m for a 2 pipe system

The Riello instructions I have suggest both 1 and 2 pipe can do a 4m lift

[Dave Liquorice]

Ah good point ... B-(

[Dave Liquorice]

Yes, quite thick glass, around 1/4", IIRC. It's mostly full of oil, currently it's got about a teaspoon of water lurking in the bottom. It would have to get very full for the expansion on freezing to be a problem and as I check it and the tank level every week that isn't likely to happen.

[F Murtz]

Is it possible that the take off point is above the bottom of the tank to stop using the dregs in case of water in the tank?