Virage fuel pump alternatives

HI everyone!

Thanks for the discussion above, I've been playing with my silly R12 and a elec pump has been on my shopping list for a while. Thinking of the eventual twin 45's she'll have, I went and got a nice rotary vain carter elec pump that should be more pump then I will ever ever ever need. Now to find a way to shut it off when I flip it / a lpg safety switch and I'll be cool.

Couple of questions however;

1) I'm trying to understand how these are different to a simply relay. Do they have a capacitor or something built in that manages the pulse from the coil thus maintaining the open circuit? Why not just run a capacitor before a standard relay?

2) I'm trying to create a situation where I can prime the system before wasting precious battery amps by cranking. The shit race car sits for weeks at a time without use. Or are those of you with fitted elec pumps saying cranking time is reduced simply by the efficiency these things have so, no big deal, keep it lower then the tank and go nuts / you wont have a delay in starting.

Ignorantly yours,

Dan


I still like the idea of a fuel pump switch on the dash like an old aeroplane.
 
Turn on the ignition. Wait. The electric pump fills the carby and the noise stops. Then turn the key and start.

That's the whole point, with an electric pump it primes the system before you crank the engine. That is, you don't use the starter motor as a fuel pump. Dunno about the relay cutting out the pump after your accident if the ignition is still on - that was too sophisticated for me.
 
Oh Dan you Muppet :s

That is indeed the whole point, sorry and thank you John.
 
bowie said:
HI everyone!

Thanks for the discussion above, I've been playing with my silly R12 and a elec pump has been on my shopping list for a while. Thinking of the eventual twin 45's she'll have, I went and got a nice rotary vain carter elec pump that should be more pump then I will ever ever ever need. Now to find a way to shut it off when I flip it / a lpg safety switch and I'll be cool.

Couple of questions however;

1) I'm trying to understand how these are different to a simply relay. Do they have a capacitor or something built in that manages the pulse from the coil thus maintaining the open circuit? Why not just run a capacitor before a standard relay?

2) I'm trying to create a situation where I can prime the system before wasting precious battery amps by cranking. The shit race car sits for weeks at a time without use. Or are those of you with fitted elec pumps saying cranking time is reduced simply by the efficiency these things have so, no big deal, keep it lower then the tank and go nuts / you wont have a delay in starting.

Ignorantly yours,

Dan


I still like the idea of a fuel pump switch on the dash like an old aeroplane.
Click to expand...

The relay has a solid state circuit inside it that excites the relay coil to close the relay contacts and provide power to the pump when the motor is running.

Generally the current carrying side would be wired similarly to a standard relay in that it has a 12v supply from the battery fused to provide current that is able to run the pump. The pump is connected to the switched contact. The switching side is where the magic happens. It is a solid state circuit, and will have a ground wire, and a positive connection to the ignition switch, these will supply the circuitry with power, to allow it to make the decision of when to energize the relay coil. Another wire will run to the negative side of the coil, or somewhere that supplies pulse when the motor is running. This wire will feed the circuit with the pulse similar to a tachometer, and the circuit will determine from the pulses it receives, if it is to switch the fuel pump on.
Some of these relays also have a connection to the starter circuit which will also trigger the pump when the starter solenoid is energized (Bosch ones used in lost of French cars certainly do). Also, many have a timer circuit built in which will run the pump for a short time (3ish seconds) when power is first applied to the switched positive to allow “priming“. I don’t think the LPG ones have the start sense wire (If you really wanted I’m sure you could add a diode to allow this though), and am not sure if they allow the 3 second priming either. Although, as the pumps are normally able to supply ample volume it may not be required.
 
There's also the option of fitting an oil pressure activated switch. When pressure drops below the threshold value (pretty generous as in low so you can crank the engine with the pump operating) when the engine stalls/stops for whatever reason, the circuit is cut and the fuel pump stops.

Tachy relays have a sensing circuit to see if the coil is sending out pulses (i.e. the dizzy is spinning). If the pulses don't exist, the relay doesn't energise the pump. Can make life a bit more difficult if the coil or dizzy have problems, it can leave you without fuel too. Which is not necessarily a bad thing (engine can't run anyway), but can make diagnosis a bit harder.

Dan, If I were you I would go with the oil pressure switch. More reliable and better suited to racing applications. Might have to baffle your sump to make sure you don't have oil surges/pressure drops in high g cornering/braking situations.

If you run a capacitor you won't have power to the pump. Remember, capacitors block DC. This is taken care of by the tachy relay.

To prime without cranking, you can have a separate on/off switch operated by hand that bypasses the pressure switch/tach relay (you need to manually switch it off) or a separate wire running from the ignition switch in accessory position. I would go for the manual switch because otherwise whenever you have the ignition in ACC you are pumping fuel and you may want to perform some checks or other things without necessarily wanting to start the car. Just wire in series a big red warning light and put that on the dash in front of you so you don't forget the switch on. That will also tell you if there is power to the pump.
 
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Thinking about this, I already have an oil pressure switch installed in the block. I can wire a "normally open" relay to trigger from that big ol' red light i have on the dash that is activated by the collent temp and oil pressure sensor.

Thus if it overheats / drops oil pressure (engine stalls) fuel will shut off.

Sounds good to me.

As you mentioned I'll install a separate master to turn everything on, and get to full-fill my old aeroplane fantasies.


oh wait... I should check if that is a pressure or just a low oil level switch. hahaha!
 
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