electric fuel pumps

[JIM NEWMAN]

This probably falls into the stupid question or "who cares" category but it's bugging me.
The LBCs with which I'm familiar have the pumps that produce the ticking noise: high rate when priming the system, a steady periodic tick when the engines running. Why they do that? Why don't the fuel pumps on "ordinary cars" do that. It's sometimes a comforting sound but its sometimes frankly annoying. What's the deal? Do the pumps on later model Healeys and say XKEs make that same sound?
jim

 

[Bugeye58]

The old tickety tickety tickety tick.........tick...........tick......... fuel pumps that we know and love so much are essentially "demand only" type pumps. They pump until a preset pressure shuts them off, and then only cycle again when the engine actually needs fuel. There is a certain amount of bleed built into them so they do cycle occasionally when the engine isn't running but the pump is on, to keep the contact points from welding themselves together.
Current production vehicles are generally fuel injected, and the fuel pumps are constant delivery types, as the fuel delivery to the engine is determined by the opening and closing of the fuel injectors. Injectors require a constant head of pressure to ensure instantaneous fuel delivery on demand, so the pump runs continuously. As injectors pulse for only milliseconds, pressurized fuel has to be available at all times. Fuel that is not being used is routed back to the tank via a return line, and also is used to cool the injectors.
Probably way more than you wanted to know, right?

Jeff

[ 12-14-2003: Message edited by: Bugeye58 ]</p>

 

[Dave Russell]

Tickety tick- Tickety boo

In addition to jeff's explanation, there are two main types of pumps. Rotating & reciprocating. The reciprocating types go tickety tick as the diaphragm (or sometimes a piston) cycles back & forth. The rotary type (usually centrifugal or vane type) have a continuous motion so no tickety.

Later model Healeys & XKEs still have the SU reciprocating diaphragm type of pump. Later model fuel injected cars Usually have rotary type pumps & whine instead of tickety. The stock engine mounted diaphragm type pump reciprocates but you just don't hear it.
D
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by JIM NEWMAN:
Why they do that? Why don't the fuel pumps on "ordinary cars" do that. It's sometimes a comforting sound but its sometimes frankly annoying. What's the deal? Do the pumps on later model Healeys and say XKEs make that same sound?
jim<hr></blockquote>

 

[Jim Weatherford]

There is also a fuel pump I just don't get, those are the ones that are installed inside the fuel tanks, they just seem dangerious to me and besides I like the ticking, somehow I know it's working when I turn the pumps on... until it doesn't. My Cobra replica had twin Bendix fuel pumps mounted in the trunk and while they could be heard before starting the car, once the 428 CDI engine growled to life, you didn't have to worry about hearing fuel pumps.

The exterior mounted pumps are easy to replace and cost approx. $125. to $150., those inside the tanks are very expensive as the tank has to be dropped and... well you know $$$. You know the pumps that are inside the tanks cost the same but you have to add approximately another $125. and up for labor. Don't ask me how I know.

 

[bob walker]

The reason the fuel pump in a gas tank is not dangerous is because the environment is above the UEL (upper explosive limit) due to the high concentration of gasoline fumes in the tank.

If you think about the needs for a fire or explosion, you need an ignitor (spark), fuel gasoline) and an oxidizer (oxygen in the air). As the concentration of fuel increases, there is initially not enough fuel to explode, and you are below the LEL (lower explosive limit), as the concentration of fuel increases in the explosive region, at some point there is too much fuel and not enough oxidizer, and you are above the UEL.

People do things like take a lit cigerette and quickly dunk it in a full cup of gasoline and douse the cigerette without lighting up the gasoline to demonstrate this point (no air, no combustion). DO NOT TRY THIS. The lit cigerette has to pass through the mixture of fumes above the cup that CAN ignite.

And regarding that fuel pump in the gas tank thing, I don't like it either. The symptoms of a fuel pump breaking down are the same as running out of gas, so one tends to fill the tank. I did this outside Cathredal City, Ca on a trip to LA, and got stuck overnight. I had to wait the entire next day to get my fuel pump replaced as the shop it got towed to could not siphon the gas out due to the anti-theft measures in the gas tank, and had to wait until the end of the day for the shop to be willing to remove the full gas tank to avoid fire danger and be able to replace teh fuel pump.

I did meet the guy that actually designed the fuel pump in the gas tank in the course of my job, and told him it was a stupid idea, hope that helps...

Bob Walker

 

[Jim Weatherford]

Bob Walker;

Thank for the details, I appreciate it and that you told the guy off is even better. I was involved in the auto engineering and consulting business for many years and not every idea implemented is worth dealing with, that's for sure.

 

[carrottop]

I also rely on my tickety tick fuel pump for more than its intended function. You may remember a long thread on this forum a while back regarding the reliability of the Smiths fuel gauge. When I'm almost down to a 1/4 tank of gas, I generally fill up as I know my fuel pump will start to tick frantically which is a the final warning!

Eric

 

[JIM NEWMAN]

Getting back to the "tickety tickety tick tick" issue....
I appreciate all the tech input but whether it's an eccentric vane, diaphragm or whatever pump, the question for me still remains - why?
As far back as 1959 when I had my '54 BN2 I also had a '52 Pontiac. It didn't have fuel injection and the fuel pump made no discernable noise. Every normally aspirated car I've had in the interim, except LBCs, don't do the tickety tick routine. The question I guess is, why would BMC, for example, opt for this kind of fuel pump as opposed to other (silent, non-ticking) types that were obviously available?
Just curious.......
jim

 

[Dave Russell]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by JIM NEWMAN:
the question for me still remains - why?
As far back as 1959 when I had my '54 BN2 I also had a '52 Pontiac. It didn't have fuel injection and the fuel pump made no discernable noise. --- why would BMC, for example, opt for this kind of fuel pump as opposed to other (silent, non-ticking) types that were obviously available?
Just curious.......
jim<hr></blockquote>
Jim,
A couple of points -- Pun?
Domestic makers of the earlier era used mechanical, engine driven diaphram pumps. They made no noise, didn't last particularly long, leaked fuel into the crankcase, often had limited capacity, & required 5 minutes of engine cranking to fill an empty carb after it had been sitting. Some hot rodders (most) replaced these pumps with the available aftermarket electric pumps which were available at the time. The Stewart-Warner was a diaphragm pump, the Bendix was a reciprocating piston type & they both clicked. Most folks considered the ticking to be a small price to pay for having a "better" pump.

The domestic cars retained the mechanical pump until the advent of fuel injection when a much higher pressure & instant on pump was needed. They then went to a rotary electric pump. Somewhere around this time a "wise guy" decided to put this pump inside of the tank. Why? - to keep it quieter, & it is more efficient as a pusher than as a puller, & possibly cheaper. The pusher keeps the entire fuel line pressurized & makes the system less subject to vapor lock.

The European makers went with the tickety electric pump from a very early time & appear to have been happy with it. Others have pointed out that the ticking is actually quite comforting to them. Why ticking? - Tradition, if it works leave it alone, why did the English do "anything the way that they did?" If it really bothers you there are external rotary electric pumps available for you to upgrade to. Be glad that it isn't mounted inside the tank.

This subject could be discussed forever.
D

 

[Roger]

Many electric pumps tick, and all is explained above. Most mechanical pumps don't, and manufacturers choose which to fit. Most British manufacturers fitted both, choosing which models to fir with which type. Many British engines have provision for (usually) camshaft-driven fuel pumps bolted to the side of the block. Somtimes there's a bolt-on plate covering the hole when an electric pump is used, and sometimes the block casting is modified, though you can often still see the bump. I think most BMC A-type blocks show signs of the pump mounting.
Which pumps did they choose? SU-carburetted engines often, but not always, had complimentary SU tick-type pumps. Often SU-carburetted engines were more "sporty" than other makes, though not always. Minis had SU Carbs & pump, for example, but not always.
Sorry if it ticks you off - sell the car, I woould!