Talk:Fuel pump

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Question of safety[edit]

If submerging the pump in liquid gasoline is safe because the liquid does not explode, what if your tank is getting empty? Is it not as safe then?

My question exactly. I recently took an electric fuel pump apart because it wasnt working. The fuel actually flows through the windings and brushes of the pump which is actually just a tiny motor. I cannot believe anyone would invent such a device. When the tank is almost empty it is full of explosive vapors. The tiny fuel pump itself is sealed on each end by crimping the outer casing against o-rings. If the top o-ring were to fail and the fuel was at a level below thw top of the pump, the pump motor would spark when turned on. I am going to go read up on intank fuel pump explosions and see just how common it is.
The almost empty tank is not technically full of explosive vapor - the air, or oxygen supply, is probably far too low to create an appropriate mixture. In fact, if the cap has not been removed, the fumes should all be gasoline and no air/oxygen at all, due to modern sealed fuel systems developed to reduce emissions of volatiles. Still, I agree that it seems scary, especially when you have to work in an opened fuel tank to replace or repair the pump! human 20:08, 19 November 2006 (UTC)
Most flames can't travel through a gap of less than 1/4 inch wide between surfaces unless they are already really hot. I've done experiments on this. You have to have the fuel to air mixture just right. Considering how small the hole in the o-ring would be, it's highly unlikely that the flame could travel beyond the insides of the pump. Plus, the voltage going through the motor is on the order of 1,000 times less than the voltage going through your spark plug. You're not going to get a strong spark. You're more likely to have this happen if you had someone smoking while trying to fill up a tank. The filler stem might be big enough to allow a flame to backflash into the tank. Smilla0 04:33, 18 August 2007 (UTC)
I designed fuel pumps at Ford for 10 years. The explosive nature of a fuel tank is not a fact due to the low amount of 0xygen in the tank. All cars have the same "design" fuel pump (a small motor turning a device - usually a turbine or gerotor). However, this is one reason why you turn off your vehicle when filling it and DO NOT go back into your car until the fill is complete. The likelyhood of generating a spark (from the interior of your car) goes up dramatically. A static spark at the fillerneck is NOT something you want to happen. I have seen gas station videos - believe me....
I am an auto mechanic who also has a chemistry background. The reason electric, tank- mounted fuel pumps do not cause explosions is that the concentration of fuel vapors is too high to allow an explosive mixture. The volatile (which in this context refers to a tendency to evaporate) nature of gasoline causes fuel vapors to take up any empty space as the fuel tank is emptied. Even if you completely empty a tank, open its access ports, and allow it to sit open, the concentration of vapors INSIDE the tank will still be too high to explode. Now, OUTSIDE the tank is a different story, and for this reason, one must use caution when performing any sort of repair or maintenance to a fuel tank, regardless of the type of pump used on the vehicle.

Another area of the article that I feel needs clarification/ changing: From the section "Decline of the Mechanical fuel pump:" "Electric fuel pumps will run whenever they are switched on, which can lead to extremely dangerous situations if there is a leak due to mechanical fault or an accident. Mechanical fuel pumps are much safer, due to their lower operating pressures and because they 'turn off' when the engine stops running." This statement would be true if electric fuel pumps were merely energized by the ignition switch of the vehicle. (whether through a relay or not) But I know of no automobile equipped from the factory with such a design. What is used instead is as follows: When you initially switch on the ignition switch, the vehicle's PCM or less commonly, a timer circuit, (depending on the vehicle) energizes the fuel pump relay for a few seconds in order to pressurize the system for starting. Then, when the engine is rotating, one of the speed sensors (either camshaft or crankshaft, or even distributor pickup coil on older vehicles) provides a signal, either directly or through the PCM, to the relay, which powers the pump. In the event that the engine stops running, so will the pump. Some vehicles- primarily Fords, have a further safeguard in the form of an "inertia switch" that switches off power to the fuel pump after an impact of sufficient force is sustained. This switch has to be manually reset in order to resume operation of the vehicle. Therefore, the statement that "Mechanical pumps are much safer" is incorrect. It is true that some hobbyist builders of performance cars, as well as backyard mechanics attempting to repair a car without proper ability or knowledge, will often incorporate an electric fuel pump that is powered directly by the ignition switch, but the hazards of this situation aren't due to the design of an electric pump, but rather the lack of knowledge of/ willful disregard of automotive engineering protocols on the part of the person who creates the situation. These are the same people who used to do unsafe things on vehicles with mechanical pumps, such as replace the steel fuel line from the pump to the carburetor with a rubber one, routed near the hot exhaust manifold. Again- not the fault of the pump design, but rather the fault of the brain trust that did the work.75.60.242.247 (talk) 21:28, 26 February 2011 (UTC)

Every Volvo B18 or B20 engine I have ever seen, new from the factory or old, has a rubber hose between the fuel pump and the carburetor. — Preceding unsigned comment added by 208.53.195.38 (talk) 17:44, 13 October 2011 (UTC)

this has been happening for about a year now. After we would be driving along the freeway for a while, all of a sudden the engine would start to lose power. Then after we would stop and shut off the car and restart it, it would work fine for a bout 10 minutes and then it would do it again. after the first time it started doing this, she got it to a mechanic and found out that the fuel filter was so clogged that the mechanic couldn't even blow through it. And it's still doing it today, only when were driving on the freeway, but not on other roads that are not as fast. would that indicate damage to the fuel pump?

I don't think this is the appropriate venue for asking car repair questions. Might I suggest searching for discussion groups focussed on your particular brand/model, where there will be people familiar with its quirks and the venue will be intended for solving such problems? Such sites abound, and many are incredibly helpful. human 20:08, 19 November 2006 (UTC)
PS, please sign your comments with four tildes (shifting the key to the left of the "1" usually makes a ~ tilde).

Sources[edit]

I'm not adding these as footnotes since I'll probably botch the formatting, but here are a couple of places to look at. Most of the descriptive text seems to be lifted wholesale (copyvio!) from http://dragtimes.com/fuel-pump.php

There is also some info about safety circuits at http://www.misterfixit.com/fuelrlay.htm human 20:13, 19 November 2006 (UTC)

The dragtimes.com link you mentioned says 'Reference: wikipedia', so it was perhaps they who did the lifting. 64.126.79.209 (talk) 16:44, 15 March 2008 (UTC)

Mechanical Pump edit[edit]

I removed a sentence which was at the start of the section "Mechanical Fuel Pump", which had the text "Chrysler fuel pumps are modulated at 12 psi." It was very very much out of place: It did not explain what it meant by "modulated", it had no direct relevance to the paragraph it was in, and it was a silly start to a section. -----Saibot —Preceding unsigned comment added by 71.31.201.50 (talk) 22:50, 1 September 2008 (UTC)

Article needs sectioning[edit]

I think the article needs to cover three types of fuel pumps, the old mechanical(vacuum actuated) pumps for gasoline enginse, the newer electronic pumps, and a third section that covers high pressure fuel pumps for diesel engines. These are all distinctly different and the article does not yet contain sufficient info on the diesel pumps. --71.38.174.228 (talk) 22:40, 14 November 2009 (UTC)

I found this section which made no sense: 'This further reduces the chance of the fuel boiling, since it is never kept to be controlled via pulse-width modulation of the pump voltage.[1] This increases the life of the pump, allows a smaller and lighter device to be used, and reduces electrical load.'

It seems to have been 'damaged' by 210.89.70.46 on 3 September 2008. I'm putting back what was originally there, which is:

'This further reduces the chance of the fuel boiling, since it is never kept close to the hot engine for too long.

The ignition switch does not carry the power to the fuel pump; instead, it activates a relay which will handle the higher current load. It is common for the fuel pump relay to become oxidized and cease functioning; this is much more common than the actual fuel pump failing. Modern engines utilize solid-state control which allows the fuel pressure to be controlled via pulse-width modulation of the pump voltage.[1] This increases the life of the pump, allows a smaller and lighter device to be used, and reduces electrical load.'Wodawik (talk) 11:12, 2 October 2010 (UTC)

Electric pumps[edit]

I found this section which made no sense: 'This further reduces the chance of the fuel boiling, since it is never kept to be controlled via pulse-width modulation of the pump voltage.[1] This increases the life of the pump, allows a smaller and lighter device to be used, and reduces electrical load.'

It seems to have been 'damaged' by 210.89.70.46 on 3 September 2008. I'm putting back what was originally there, which is:

'This further reduces the chance of the fuel boiling, since it is never kept close to the hot engine for too long.

The ignition switch does not carry the power to the fuel pump; instead, it activates a relay which will handle the higher current load. It is common for the fuel pump relay to become oxidized and cease functioning; this is much more common than the actual fuel pump failing. Modern engines utilize solid-state control which allows the fuel pressure to be controlled via pulse-width modulation of the pump voltage.[1] This increases the life of the pump, allows a smaller and lighter device to be used, and reduces electrical load.'Wodawik (talk) 11:13, 2 October 2010 (UTC)

Two fuel pumps with different volumes[edit]

The article states: "(and some fuel injected engines have two fuel pumps: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine)"

I understand why the pump just before the engine would need higher pressure than the one supplying from the tank. But their volume will always be the same, right?

Velle (talk) 09:03, 2 July 2011 (UTC)

Electric fuel pump diagrams needed.[edit]

Photo and best description -http://www.aa1car.com/library/fuel_pump.htm http://hot.ee/bensiinipump/Fuel_Pump_Renovation_1_eng.htm links to video - http://www.youtube.com/watch?v=QbzEeWy1b3o

--Ericg33 (talk) 12:34, 3 December 2011 (UTC)