Lotus Elan

How does a solid state petrol pump work.

PostPost by: ericbushby » Fri Mar 30, 2018 2:17 pm

dscf0479.jpg and
I have become fed up with priming the Weber carburettors after a few days out of use. Sometimes the fuel level has gone down by 15 mm due to evaporation into the airbox.
I have resorted to removing one of the brass strainer covers on the top of the carb. and adding fuel with a small jug in order to reduce the cranking time before the engine fires or runs smoothly.
I have now fitted a cheapo. `Facet type` cube pump from ebay in the spare wheel well.
This type of pump fits neatly between the diff. access hatch and the petrol tank.
The pump is supplied via a spring return toggle switch under the dashboard.
It works very well and fills the carbs in a few seconds, so the engine now starts immediately.
Now eventually I come to the question.
Another reason I chose this type of pump is they are said to be noisy, so i would be able to hear when it stopped pumping.
It does not stop, although the sound changes when there is no fuel flowing.
I expected it to tick when it was pumping and then go silent when no fuel was needed.
It behaves the same when bench tested regardless of attidude or rotation.
It is described as a solid state pump, but i think that only refers to the coil being energised with a transistor instead of the pair of contacts as before.
Does anyone know what is happening or how it works?
Just curious,
Eric in Burnley
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PostPost by: 69S4 » Fri Mar 30, 2018 3:02 pm

On my Facet pump the ticking goes berserk when it's filling the carbs (Strombergs for me) after a layoff. It slows down but still continues to tick at a lower rate (about 2 ticks / sec) when the carbs are full.
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PostPost by: alan.barker » Fri Mar 30, 2018 3:30 pm

Eric,
on my Sprint fhc i have added a Fuel Bulb Primer as for Outboard Motors in the boot. A few pumps to prime carbs and starts no problem + no noisy pump :mrgreen: .
If you want to fit an Electric Pump "Huco is the only silent way", these are special for Weber Carbs (low pressure).
Alan
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PostPost by: ericbushby » Fri Mar 30, 2018 3:47 pm

Alan
Thank you, yes I am aware of the bulb method, but I was not satisfied with options of where to put it safely.
I chose this type of pump partly because they are reputed to be noisy, so that I could hear when the carbs were full from the drivers seat. That works as intended. I am just puzzled why it continues to tick when the carbs are full if I hold the switch on.
Like your bulb, the pump is not in use at any other time except for the few seconds it takes to prime.
Regards
Eric
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PostPost by: Billmack » Fri Mar 30, 2018 5:04 pm

It just works. It can be quieted dramatically by adding a pair of rubber mounts found on many modern car fuel pumps. Also be careful of pressure. Use a low pressure pump or an inline regulator.
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PostPost by: ericbushby » Fri Mar 30, 2018 5:13 pm

Thank you Bill,
OK I am prepared to accept that it just works unless someone knows more than us, but I was interested to know internal workings. If it packs up I will cut it open.
In my case I wanted a noisy pump, and I do have a Filter King fitted.
Cheers
Eric
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PostPost by: JonB » Fri Mar 30, 2018 5:45 pm

I wonder if it has the right sort of cutoff switch?
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PostPost by: Esprit2 » Fri Mar 30, 2018 6:11 pm

An old-school electric pump with breaker points (ie, the old SU pump), the points are just a mechanical switch driven by the same solenoid that drives the pump diaphragm. The diaphragm is spring biased in the direction that will cause it to push the breaker points closed. Once closed, the points feed electric current to the solenoid that pushes the diaphragm the other way, pumping gas, and eventually opening the breaker points. When the points open, the current is switched off, and the diaphragm return spring pushes back to eventually close the points again. The points power the solenoid that operates the points.

Breaker points are on-off.
A transistor is on-off.
So it shouldn't be real hard to envision the similarity. The difference is there's no movement in the transistor, so how does the moving diaphragm trigger it? There needs to be a sensor, and that could be a magnetic switch, a Hall Effect Sensor, etc, etc. There's more than one way to sense position 'solid state', so you'll have to research the details of your one pump.

In either case, a solenoid powers a diaphragm/ piston/ rotor... something that does the pumping. The solid state part is just the switching.

*~*~*~*~*~*~*~*~
Electric fuel pumps push fuel better than they pull it. If an electric pump is mounted high in the car, above tank level, then on start-up, it must suck fuel up to it's level (self prime) before it can 'push' it out into the plumbing to the carb(s). Self-priming and filling the carbs will take less time on first start if the pump is located down low, as close to the bottom of the tank as possible. Always plumb to 'push'.

There are small inline one-way check valves that can be installed adjacent to the discharge side of the pump. That will help minimize the fuel drain-back when the car is off/ parked, and that will minimize the amount of time required to prime the system when the key is switched on.

Rotary pumps are arguably quieter than the clicker types, but they all make some noise. Avoid mounting a pump to the body shell, which will act like a drum. Instead, mount it to the chassis so the body-to-chassis mounting pad will help dampen the noise. Also, mount the pump on rubber Lord mounts. A grommet with a thru-bolt is of little help, since the thru-bolt still provides a direct mechanical path for noise. A Lord mount has separate studs insert molded into opposite sides of a rubber puck. There is true rubber isolation with no metal to metal contact.

For the really noise sensitive folk:
Different size and durometer Lord mounts dampen or pass different frequencies. If the pump is mounted to a small, intermediate metal plate with one size/ durometer Lord mount, and the plate is then mounted to the chassis with a different size Lord mount. The noise transmitted by the first size Lord mount won't be of the correct frequency to be readily transmitted by the second size mount. The minimum of noise will be transmitted to the chassis, and the body to chassis padding will take out some more of what made it through to the chassis.

Vintage electric fuel pumps just switched on with the ignition switch. There were few if any safety over-rides. It would be wise to add an inertia switch, flow-loc valve and oil pressure switch to turn off the fuel pump in the event of an accident, or if the engine quits with the ignition still 'On'.

Regards,
Tim Engel
Last edited by Esprit2 on Fri Mar 30, 2018 6:30 pm, edited 1 time in total.
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PostPost by: joe7 » Fri Mar 30, 2018 6:14 pm

Eric, go to the LLC Facet website for more info. Also Facet recommends that the outlet should come from the bottom of the pump.
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PostPost by: ericbushby » Fri Mar 30, 2018 6:40 pm

Tim,
Thank you for your comments.
I understand and agree with most of what you say.
What puzzled me was if it is a piston charging a spring, then with no fuel flowing, the piston would not return to the sensor position and the pump would be silent.
It is not, It continues to tick quietly although no fuel is passing through. (bench test with outlet blocked and pump full).
I can see no need for non return valves as there are already two in the engine driven pump and two in this new pump all in series.
I see no need for safety equipment in this case as the pump supply is disconnected at the spring return switch under the dashboard which is only used for a few seconds for priming. There is no electric supply to the spare wheel well or the pump at any other time. At this time the engine is not running.
I just find it curious when it did not behave as I expected.
Thanks
Eric
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PostPost by: ericbushby » Fri Mar 30, 2018 7:37 pm

Hi. Joe7
oddly I could not find that Facet website; I only kept getting adverts.
However this pump is not labelled as a Facet It is a cheapo copy at 1/4 of the price. They are sometimes advertised as `Facet type`. ebay no 281923549589.
Except for the label, it is identical in every way, the crimping of the case, the tag on the black wire. the inline filter which is sometimes included and the supplied accessories are all the same.
I accept that it is upside down, but it is below the fuel level and seems to pump well, so i will leave it like that for now.
On the bench it did not seem to mind which way up it was.
Thanks anyway
Eric
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PostPost by: Elanman99 » Fri Mar 30, 2018 8:15 pm

I took my Facet pump apart about 25 years ago (I had the casing re-plated) and from what I recall the fuel wetted parts of the pump consists of an in-line arrangement of two non return valves with piston sat between them. If the basic design has not changed then dismantling is just a matter of unscrewing the two large hexagonal bosses.

The piston shuttles back and forth because it is the iron core of a solenoid. I presume it is spring loaded to one end and when power is applied shoots to the other (outlet end) pushing fuel with it, I am not sure what senses that it has reached end of travel so turning of power, but the spring returns the piston to the start position where the power is again switched on. The piston is a fairly loose fit in its cylinder (that the solenoid coil is wound on) which then limits the pressure the pump can produce. It also explains why it never really stops because when the carbs are full and there is no flow, fuel leaks past the piston whilst the spring is pushing it.

One other thing I remember is that one of the non return valves was actually within the piston itself. In the nearly 50 years that I have used this same Facet pump it has been 100% reliable. I did once have a problem with the piston sticking but that was a self induced fault caused by me having aluminium swarf in the petrol tank and having no filter on the inlet.

Ian
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PostPost by: Esprit2 » Fri Mar 30, 2018 8:20 pm

ericbushby wrote:I understand and agree with most of what you say.
What puzzled me was if it is a piston charging a spring, then with no fuel flowing, the piston would not return to the sensor position and the pump would be silent.
The spring/ solenoid/ switch/ relationship is complete within itself, and doesn't depend upon fluid in the piston/ cylinder pushing back. The spring and the solenoid work in opposition to one another, and the switch/ piston/ fluid go along for the ride.
ericbushby wrote:I can see no need for non return valves as there are already two in the engine driven pump and two in this new pump all in series.
I should have read more carefully. I thought you were replacing the mechanical fuel pump with an electric one, but you were just adding an electric priming pump. I probably jumped to that conclusion due to my own bias. I don't have much (any) respect for the mechanical pump (it needs help to work well, like from a priming pump), and my preferred solution is to dump it entirely and install a quality electric pump and control circuit.
ericbushby wrote:I see no need for safety equipment in this case as the pump supply is disconnected at the spring return switch under the dashboard which is only used for a few seconds for priming. There is no electric supply to the spare wheel well or the pump at any other time. At this time the engine is not running.
As a priming pump only, operated by a momentary switch, it doesn't need a safety system... other than making sure the momentary switch can't crush/ jam 'On' in an accident. For any full time electric fuel pump, it's wise to add a safety over-ride. The parts are all off-the-shelf.
ericbushby wrote:I just find it curious when it did not behave as I expected.
I think the pump's function is normal, it's your expectations that need fine tuning. ;-)

Regards,
Tim Engel
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PostPost by: ericbushby » Fri Mar 30, 2018 11:07 pm

Tim,
I think I have got a grip now of how it works, I must have been asking too much. The leaky piston suggestion from Ian explains it well.
Thank you for all that, you see I just need to know how things work especially when they don`t respond as I expect.
Thank you
Eric
Last edited by ericbushby on Mon Apr 02, 2018 3:21 pm, edited 1 time in total.
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PostPost by: Bigbaldybloke » Sun Apr 01, 2018 12:52 pm

Slightly off topic, but related, several people have mentioned on here about a safety cut off device if fitting an electric fuel pump. What have people found to be the best and simplest to install?
Change is inevitable, except from a vending machine!
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