Cleaning hydraulics rapid question

406 V6 · Unread post by **406 V6** » 26 Feb 2005, 18:31

Guys, someone told me that petrol could be used instead of hydracleaning for the job, although driving for only 20kms.
Is this safe?!

Mosser · Unread post by **Mosser** » 26 Feb 2005, 19:35

Wow!, i would be really concerned about having petrol in lines that are used for braking and steering and suspension, just imagine if something went wrong and caused a fire, your insurance company would instantly invalidate your insurance and i'm sure you would be prosecuted for something that would likely end in a prison sentence for endangering the public,
Not a good idea even if it works and the seals stand up to it

jeremy · Unread post by **jeremy** » 26 Feb 2005, 21:00

Should encourage you to keep air out of the system! - no oxygen - no oxygen - no explosion! I never thought of it before but perhaps this is why Citroen fill the spheres with Nitrogen.
Seriously no doubt there are many things that people have got away with but you're not going to get recommended. Besides the seals in the brakes there are miles of flexible return pipes that you shouldn't risk damaging (and a re a complete pain if you do.)
Petrol has very poor lubricating properties which is why petrol injection systems took so long to develop. The hydraulic system relies on close tolerances between metal parts to work and a little wear will lead to problems! the pressures are enormous - Around 2000 psi in parts (ie same or greater than mechanical diesel injection pumps.
Jeremy

406 V6 · Unread post by **406 V6** » 26 Feb 2005, 21:33

Well it confirms my first thoughts: the guy is nuts!
Saving some euros isn't enough of a reason to rebuild the system or for the danger of it.

crapday · Unread post by **crapday** » 26 Feb 2005, 21:56

the heat that the petrol will be under will ignite it especially if air gets into the system. not a very intelligent thing to do.

tomsheppard · Unread post by **tomsheppard** » 27 Feb 2005, 01:07

Yes Jeremy, Nitrogen was chosen for just that reason by Paul Mages when the system was designed.
Add to that the sub micron tolerances of the metal bits in the system and petrol will be the worst thing to use. A pump leak at 3,750 PSI will provide a mist that should ignite readily on the exhaust manifold and the gallon in the reservoir should torch the bonnet a treat!
And it is most unlikely even to get things clean!

adamskibx · Unread post by **adamskibx** » 27 Feb 2005, 01:45

Im confused. Why would Citroen fill the spheres with Nitrogen to avoid a fire when LHM doesnt burn? They dont seriously think that people are going to fill the system with petrol do they? I always thought it was because Nitroegen had better springing properties than 'air'. Please explain im curious now!

Unread post by **alan s** » 27 Feb 2005, 02:30

Guys,
I suspect there may be something getting lost here in the translation.
A few years ago we had someone from one of the Latin American countries make the same suggestion & claim it was common practice because they don't get hydraflush.
Subsequently we discovered it was what they refer to as a low grade dieseline. We then had a few others say it was common ih other countries and argue it was safe until a guy in Malaysis took a BX for a test drive with a view to buying, returned to the garage, revved the motor whereupon it exploded in a fireball burning the car and half the car dealership out due to a HP leak in the brake/suspension circuit.
After that. I haven't heard of it being used up until now.
Don'rt drive the car and get it out <b>FAST!!</b>
Alan S

jeremy · Unread post by **jeremy** » 27 Feb 2005, 13:46

In their liquid phase all gasses behave the same but the choice of nitrogen for the springing medium was probably influenced by considerations such as chemical activity (Nitrogen is very nearly inert), cost, availability and ease of handling.
jeremy

bxbodger · Unread post by **bxbodger** » 27 Feb 2005, 18:00

They would have to store the stuff in the sphere factory, most likely as liquid to save space-nitrogen is a lot safer- remember, liquid oxygen is rocket fuel, and any leak of oxygen is more or less an instant fire!!!
The crew of Apollo 1 were killed in a capsule fire during training in a pure oxygen atmosphere, a tiny electrical fault and it was all over in seconds- the thought of a bursting oxygen filled sphere in an accident is pretty grim- imagine mixing it with petrol!!
Alex Moulton also used nitrogen in the Hydragas system.

406 V6 · Unread post by **406 V6** » 27 Feb 2005, 20:44

And don't forget that nitrogen is more stable than oxygene, as temperature vs volume is concerned.
That's why race cars have their tyres filled with nitrogen.

Kowalski · Unread post by **Kowalski** » 28 Feb 2005, 15:15

Compressed nitrogen is used in F1 tyres because it is more temperature stable than air because of the moisture content of the air. It is the fact that it is dry that is more important than the fact that it is Nitrogen.

ItDontGo · Unread post by **ItDontGo** » 28 Feb 2005, 15:22

Hmmm. Petrol in brake calipers at a few hundred degrees celcius. Would bring a whole new meaning to frying your brakes.

FrenchLeave · Unread post by **FrenchLeave** » 28 Feb 2005, 19:28

To clear up a couple of misunderstandings:
1. Nitrogen is not "very nearly inert". If it were, there would not be so many nitrides, nitrates and nitrites around; all formed by chemical reactions with other elements. Just think of nitric acid, ammonia, cyanide, laughing gas etc., etc.. It's strong point is that it does not support oxidation reactions - so no rust and no fire.
2. The universal gas equation PV = mRT applies to all gases, that's why it's universal. The gas constant R is the same for air and nitrogen, so the variation of pressure with volume and hence the "springing" properties, is identical for both.
3. Oxygen is not a fuel. It is safe to pass an electrical spark through a pure oxygen atmosphere because there is no second chemical to provide the fuel for an exothermic reaction; it is not safe to strike a match in an oxygen atmoshere because the match is the fuel and there will be a violent reaction.
Having said all that, I agree that gasoline has no place in any hydraulic system.

Kowalski · Unread post by **Kowalski** » 28 Feb 2005, 20:40

I always remember the ideal gas equation as
PV = nRT
Pressure x Volume = number of moles of gas x molar gas constant x temperature
http://en.wikipedia.org/wiki/Ideal_gas_equation
The thing you have to remember is that NOT ALL gases behave as ideal gases. When you add water vapour to a gas, it behaves even less ideally.