How much are they?
Mystery behaviour at petrol station
- Thread starter Vicario
- Start date
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It sounds like you have a blocked rollover valve in the breather pipe. Petrol cars have an evaporative emissions control system on the breather, and all cars have a vent pipe. Let's take the breather first.
As the car sucks fuel out of the tank, there has to be a way of letting air back into the tank, otherwise as the fuel level drops, you'll create a partial vacuum in there and sooner or later, the engine won't be able to suck the fuel out against it. Similarly, if you park the car in the sun, the air in the tank will warm up and expand, so you have to leave it somewhere to go. Early cars had the breather just open to atmosphere. This created two problems:
1. on the hot day, unbruned fuel vapour just escaped to atmosphere, causing pollution.
2. If you crashed your car and rolled it, fuel would leak out of the breather.
From the early 1990s, emissions regulations forced manufacturers to fit a "carbon can" (a little pot of activated charcoal particles in the breather pipe. The charcoal absorbed the evaporating fuel vapour). When you start the engine, a "purge valve" opens for about 10 seconds, and allows the engine to suck air backwards through the carbon can, purging the fuel vapour out of the charcoal, ready for the next time it is parked up. As Burnerman says, that vapour is just burned by the engine.
The second issue was solved by putting a rollover valve in the line (usually in the top of the fuel tank). It's just a sort of ping pong ball that floats, (or ball bearing that sinks) and it just closes off the pipe if the car is inverted. Carbon cans rarely block. it is possible if you really try hard to over-fill a car with fuel and then park it in the sun, because liquid fuel enters it and can swell the charcoal particles, but it's extremely unlikely.
The other thing is the vent pipe. This lets air out of the tank when it is being filled. Modern forecourt pumps can whack fuel in pretty fast - upwards of 40 litres per minute, some of them. The breather pipe and carbon can can't handle that sort of flow rate. So there's a much bigger diameter pipe, which goes from the top of the tank to the top of the filler neck (somewhere above where tip of the forecourt pump nozzle goes). This lets air out of the filler hole ABOVE the point where the petrol is being squirted in. If you have a problem with this pipe, the tank will be a sod to fill, and the pump will keep clicking off. Obviously, when the filler cap is closed, this pipe serves no function. This makes me think that your "pressure" and your warning light problems are the rollover valve, and your filling problem is the vent pipe. The two could of course be part of the same Assembly, in the top of the tank.
The gauge is a separate issue entirely, and fairly normal on modern cars.
As the car sucks fuel out of the tank, there has to be a way of letting air back into the tank, otherwise as the fuel level drops, you'll create a partial vacuum in there and sooner or later, the engine won't be able to suck the fuel out against it. Similarly, if you park the car in the sun, the air in the tank will warm up and expand, so you have to leave it somewhere to go. Early cars had the breather just open to atmosphere. This created two problems:
1. on the hot day, unbruned fuel vapour just escaped to atmosphere, causing pollution.
2. If you crashed your car and rolled it, fuel would leak out of the breather.
From the early 1990s, emissions regulations forced manufacturers to fit a "carbon can" (a little pot of activated charcoal particles in the breather pipe. The charcoal absorbed the evaporating fuel vapour). When you start the engine, a "purge valve" opens for about 10 seconds, and allows the engine to suck air backwards through the carbon can, purging the fuel vapour out of the charcoal, ready for the next time it is parked up. As Burnerman says, that vapour is just burned by the engine.
The second issue was solved by putting a rollover valve in the line (usually in the top of the fuel tank). It's just a sort of ping pong ball that floats, (or ball bearing that sinks) and it just closes off the pipe if the car is inverted. Carbon cans rarely block. it is possible if you really try hard to over-fill a car with fuel and then park it in the sun, because liquid fuel enters it and can swell the charcoal particles, but it's extremely unlikely.
The other thing is the vent pipe. This lets air out of the tank when it is being filled. Modern forecourt pumps can whack fuel in pretty fast - upwards of 40 litres per minute, some of them. The breather pipe and carbon can can't handle that sort of flow rate. So there's a much bigger diameter pipe, which goes from the top of the tank to the top of the filler neck (somewhere above where tip of the forecourt pump nozzle goes). This lets air out of the filler hole ABOVE the point where the petrol is being squirted in. If you have a problem with this pipe, the tank will be a sod to fill, and the pump will keep clicking off. Obviously, when the filler cap is closed, this pipe serves no function. This makes me think that your "pressure" and your warning light problems are the rollover valve, and your filling problem is the vent pipe. The two could of course be part of the same Assembly, in the top of the tank.
The gauge is a separate issue entirely, and fairly normal on modern cars.
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Interestingly they are not actually compressed air at all, if you wanted to transport compressed air you'd need a far heavier guage container. Instead to get a good volume in a thin walled container they need something which compresses down and becomes a liquid at relativly low pressures, which are generally the key attributes of refrigerants, so generally whats in there is a hydro-carbon refrigerant (usually propane) as it'll enter the atmospehere by design, so we we cannot have anything that is ozone depleteing, it does end up being flamable though, and the same is true of propellants of other sprays as well, 50 years ago they didn't really know about ozone depleteion, and thats why CFCs were used in aerosol cans, because most refrigerants were CFCs and refrigerants had the right properties for the job. Now even your fridge in the kitchen likely uses a hydrocarbon refrigerant, and you can now even buy split airconditioners that use it so that they don't require an F-gas ticket
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