Diesel fuel life.

[CAR]

Morning, not really a big saloon related topic, but I know we have forum users from all walks of life on here.
At work we have two large Perkins powered standby generators with a large (approx 31000litres) diesel tank to supply them. We have been tasked by the client to take a diesel sample from the tank for analysis.
Is there a best place to take the sample from?
I initially looked all round the engines for somewhere suitable to take a sample. Can't see one without disconnecting hoses, and I don't want to go down that road .
Did think about taking some from the fuel filter drain off but I assumed this was for water and contaminants, and I didn't want to get a false reading when tested.
If I syphon some from the tank, apart from using the correct kit (I don't want a gob full of diesel) is it better to take it from the top, middle or bottom, or does it not matter?
Lastly, does diesel have a useable life, unleaded petrol is not easy to store and 'goes off' in a matter of months, is diesel similar. I ask this as probably 70% of the 31000litres has been in there for just over 7years, and apart from 2000litre top ups, it never moves or gets mixed like it would in a moving vehicle.

Thanks Colin.

[rrhool]

I don't know where would be best to take a sample from, but I can tell you from personal experience that standing diesel can grow a fungus, like a very fine black furry substance. It was sufficient to block the fuel pick up on my Range Rover, diesel had been in tank for about 4 years. I really recomend you dont try syphoning it by mouth, diesel tastes really bad!

[mikeyb]

Diesel can indeed grow a fungus, are you able to illuminate the inside of the tank via an access hatch to determine if this has happened?

Products are available to deal with it.

Should not make much difference but I would take a sample from close to the pick up point.

Does the feed to the generators have a cut off, if so turn it off and remove the feed pipe then take a sample.

As long as the top ups are reasonably regular then there should not be a problem, the problem occurs when diesel stands and is not moving, allowing the fungus to grow.

As far as I know unless contaminated, diesel lasts years and years, I had a tractor with a tank that had not been topped up in 10 years and ran perfectly!

[kevinw]

Two observations - one from the buses at the museum and the other from my boat. The buses run on "white" diesel; the boat is on "red", which is really gas oil.

The buses can sit around for months without moving and we have never had a problem with the diesel aging. Frequently, when first restored, the fuel in the tank can be 10 or 20 years old and, again, we don't have a problem with this. Same with the boat, really, although of course, this is being mixed up all the time. I keep the tank filled (and locked!) over winter to keep out condensation as much as possible. There was a lot of scare a few years ago on the waterways with regard to diesel "bug" - the fungus that can grow if you have the right (or wrong) amount of condensation in the tank. This is a black mould that will quite quickly block filters and is a pain to clean out. I;ve not had a problem - I don;t actually know anyone who has, but there are plenty of reports on various canal forums and the suggestion is to treat diesel that sits in stagnent tanks with some form of gloop that prevents the bug from growing.

Diesel is an oil, not a spirit, so I don't think you have a problem with it loosing its volitility and I don't think it stratifies in the tank, so whereever you dip it from, it should be OK. You'll probably have a thing that looks like a filter, but with a tap at the bottom - this is called something like an agglometer (someone will be along to correct the spelling in a minute) - this is to drain any water, but if you drian off a couple of pints, you should get a decent sample of what is in the tank.

If you have to syphon it, get someone else to do it - if you think petrol tastes bad, diesel is 50x worse and it takes ages for the smell to go away. It damages your skin as well - horrible stuff really...

Kevin

[CAR]

Agglometer eh? I'm sure I have seen that mentioned in regards to the lucas pi system too......not sure on the spelling of that one Kevin-but drian I assume is drain. You really ought to get Anne to proof read your posts

Thanks for the info. on the diesel though and you too Mike.

Cheers Colin

[kevinw]

I have quite enough problems with Ann profreeding SIXappeal without messing about with my forum postings!!!! Glad it all made sense even with my garbled spelling! My usual excuse is that my keyboard can't keep up with my hi-speed typing. That or the couple of pints I drained with my dinner tonight!


Kevin

[TedTaylor]

If you are taking a sample of a liquid from a container with direct access into the top the simplest/nicest way is to insert a pipe of about 1/4 to 1/2 inch diameter into the tank to a depth to get a suitable quantity of fluid, place finger/thumb over the end to seal it, and withdraw the pipe with its slug of fluid taking care not to let any air in. You can also use a flexible pipe to go round corners into the tank (say through the filler neck) and take a sample in the same way.

Place the bottom of the end of the pipe into a suitable container and remove finger/thumb from the end and liquid will flow out of tube ...... just make sure you don't remove your digit until the tube is in the container or there will be a bit of a mess

This method has the advantage of sampling through the liquid in the tank taking samples at various depths.

You can also use this principle to start a siphon. Lower a tube into the liquid as far as possible and block the end, then if you can withdraw the pipe with enough liquid so that the level in the pipe is lower than the level in the tank then it will siphon happily. Not easy if you cannot see the level in the tank but if after a couple of tries you cannot get it to siphon then the liquid level in the tank is too low.

The reason why petrol 'goes off' in part is because the lighter fractions (those that evaporate easiest) evaporate from the liquid first so effectively producing fuel of a lower grade/octane level - you can tell this has happened because the fuel smells stale. Diesel does not have the same problem because it does not have the same volatile fractions that evaporate at room temperature.

[Charles H]

I have quite enough problems with Ann profreeding SIXappeal without messing about with my forum postings!!!!
Kevin

Profreading????????

[kevinw]

Precisely. As my hero Captain Mainwaring would say "I wondered who would notice that first".

I did put lots of errors in the post originally, just for fun - but decided that it would be more amusing to just have the one (or two)

[David Withers]

I'm no expert on this sampling business but, having spent four decades of my life at Perkins, I felt I ought to chip in...

Firstly, the fuel filter commonly fitted to Perkins engines for many years was a CAV "agglomerator" type which includes a metal-cased filter element known as the CAV 296 (full part number was 7111/296) sitting on a clear glass bowl. The bowl collects any water finding its way with the fuel into the filter unit, water being the heavier of the two liquids, and there is a tap to drain it off.

As Colin suggests, this agglomerator filter was also fitted to the Triumph PI. I retained mine after converting to carbs and can't actually recall needing to drain water out, but the car is always garaged when not in use.

I agree, a fuel sample taken from the filter could be contaminated unless the element is well flushed through first, and even then there's no guarantee. Better I think to draw off a sample through the filler, avoiding going too near the bottom of the tank as you could draw up any water, sediment or corrosion that may be lying there harmlessly.