Lift pump wiring

[Discopotatoes]

I'm just working out what I need for my lift pump to swirl pot fuel system, and was wondering what's the best way to wire in the lift pump? I've got a facet red top feeding a 2 Ltr swirl pot with a submerged 044 style pump, all an6 fuel lines and fittings.
Do I run both pumps from a single feed I'E the original fuel pump relays with beefed up wiring or separate feeds and relays?
The red top has a low amp draw so won't add much to the inline pump.
Over to you

[Steve_D]

Run separate relays and supply fuses. Fuses are there to protect the wiring. The wiring and fuse for the HP pump will be much heavier than the LP pump so if you run them together the large fuse (for the HP) will not protect the smaller wiring of the LP. Run both relays signalled by the ECU.

On the plumbing side the HP pumps have a tendency to cavitate at the inlet port particularly if the pump is not lower than, and close too, the swirl pot. This may not be quite as relevant with a submerged pump but what I'm going to suggest is still valid.
The LP (Red Top) pump fills the swirl pot and un-used fuel is returned to the tank but this does not need to happen. The only reason for the return pipe is to let any trapped air or vapour to escape from the swirl pot and return to the tank. If you put a restriction in the return pipe the LP pump will maintain a pressure in the tank which will help prevent cavitation at the HP Pump. The LP pump is internally regulated at around 7psi so there is no issue with restricting the flow as this is pretty much what happens when that pump is feeding a carb with a full float chamber.

Steve

[Discopotatoes]

Steve_D said:

Run separate relays and supply fuses. Fuses are there to protect the wiring. The wiring and fuse for the HP pump will be much heavier than the LP pump so if you run them together the large fuse (for the HP) will not protect the smaller wiring of the LP. Run both relays signalled by the ECU.

On the plumbing side the HP pumps have a tendency to cavitate at the inlet port particularly if the pump is not lower than, and close too, the swirl pot. This may not be quite as relevant with a submerged pump but what I'm going to suggest is still valid.
The LP (Red Top) pump fills the swirl pot and un-used fuel is returned to the tank but this does not need to happen. The only reason for the return pipe is to let any trapped air or vapour to escape from the swirl pot and return to the tank. If you put a restriction in the return pipe the LP pump will maintain a pressure in the tank which will help prevent cavitation at the HP Pump. The LP pump is internally regulated at around 7psi so there is no issue with restricting the flow as this is pretty much what happens when that pump is feeding a carb with a full float chamber.

Steve

Thanks Steve, my plan was to run the return fuel to the swirl pot then an an6 to the fuel tank do you think the fuel return on the tank is enough of a restriction?
the submerged pump should never cavitate as its in a vertical position surrounded by fuel as long as the lp pump and the return fuel can keep the swirl pot full on full boost

[Steve_D]

Discopotatoes said:

Thanks Steve, my plan was to run the return fuel to the swirl pot then an an6 to the fuel tank do you think the fuel return on the tank is enough of a restriction?
the submerged pump should never cavitate as its in a vertical position surrounded by fuel as long as the lp pump and the return fuel can keep the swirl pot full on full boost

I would put in a restrictor with a hole less than 1mm diameter. This should give a pressure of about 5psi.
Even with the submerged pump cavitation could still be there as the 044 pump is quite powerful.

Steve

[Discopotatoes]

Steve_D said:

Discopotatoes said:

Thanks Steve, my plan was to run the return fuel to the swirl pot then an an6 to the fuel tank do you think the fuel return on the tank is enough of a restriction?
the submerged pump should never cavitate as its in a vertical position surrounded by fuel as long as the lp pump and the return fuel can keep the swirl pot full on full boost

I would put in a restrictor with a hole less than 1mm diameter. This should give a pressure of about 5psi.
Even with the submerged pump cavitation could still be there as the 044 pump is quite powerful.

Steve

cheers

[Discopotatoes]

Steve_D said:

Run separate relays and supply fuses. Fuses are there to protect the wiring. The wiring and fuse for the HP pump will be much heavier than the LP pump so if you run them together the large fuse (for the HP) will not protect the smaller wiring of the LP. Run both relays signalled by the ECU.

On the plumbing side the HP pumps have a tendency to cavitate at the inlet port particularly if the pump is not lower than, and close too, the swirl pot. This may not be quite as relevant with a submerged pump but what I'm going to suggest is still valid.
The LP (Red Top) pump fills the swirl pot and un-used fuel is returned to the tank but this does not need to happen. The only reason for the return pipe is to let any trapped air or vapour to escape from the swirl pot and return to the tank. If you put a restriction in the return pipe the LP pump will maintain a pressure in the tank which will help prevent cavitation at the HP Pump. The LP pump is internally regulated at around 7psi so there is no issue with restricting the flow as this is pretty much what happens when that pump is feeding a carb with a full float chamber.

Steve

still trying to get my head around this wiring.
if the fuse is there to protect the wiring loom, can i use the original wiring and fuse for the lift pump then wire the hp pump of the same relay and fuse?

[Steve_D]

Discopotatoes said:

Steve_D said:

Run separate relays and supply fuses. Fuses are there to protect the wiring. The wiring and fuse for the HP pump will be much heavier than the LP pump so if you run them together the large fuse (for the HP) will not protect the smaller wiring of the LP. Run both relays signalled by the ECU.

On the plumbing side the HP pumps have a tendency to cavitate at the inlet port particularly if the pump is not lower than, and close too, the swirl pot. This may not be quite as relevant with a submerged pump but what I'm going to suggest is still valid.
The LP (Red Top) pump fills the swirl pot and un-used fuel is returned to the tank but this does not need to happen. The only reason for the return pipe is to let any trapped air or vapour to escape from the swirl pot and return to the tank. If you put a restriction in the return pipe the LP pump will maintain a pressure in the tank which will help prevent cavitation at the HP Pump. The LP pump is internally regulated at around 7psi so there is no issue with restricting the flow as this is pretty much what happens when that pump is feeding a carb with a full float chamber.

Steve

still trying to get my head around this wiring.
if the fuse is there to protect the wiring loom, can i use the original wiring and fuse for the lift pump then wire the hp pump of the same relay and fuse?

Yes use all the existing wiring to now run your LP pump but use the same signal from the ECU to trip a new heavy duty relay for the HP pump this relay should have its own supply direct from the battery and its own fuse.
Do you know what current the HP pump is going to draw? This will determine the size of relay, cable and fuse.

Steve

[Discopotatoes]

Steve_D said:

Discopotatoes said:

Steve_D said:

Run separate relays and supply fuses. Fuses are there to protect the wiring. The wiring and fuse for the HP pump will be much heavier than the LP pump so if you run them together the large fuse (for the HP) will not protect the smaller wiring of the LP. Run both relays signalled by the ECU.

On the plumbing side the HP pumps have a tendency to cavitate at the inlet port particularly if the pump is not lower than, and close too, the swirl pot. This may not be quite as relevant with a submerged pump but what I'm going to suggest is still valid.
The LP (Red Top) pump fills the swirl pot and un-used fuel is returned to the tank but this does not need to happen. The only reason for the return pipe is to let any trapped air or vapour to escape from the swirl pot and return to the tank. If you put a restriction in the return pipe the LP pump will maintain a pressure in the tank which will help prevent cavitation at the HP Pump. The LP pump is internally regulated at around 7psi so there is no issue with restricting the flow as this is pretty much what happens when that pump is feeding a carb with a full float chamber.

Steve

still trying to get my head around this wiring.
if the fuse is there to protect the wiring loom, can i use the original wiring and fuse for the lift pump then wire the hp pump of the same relay and fuse?

Yes use all the existing wiring to now run your LP pump but use the same signal from the ECU to trip a new heavy duty relay for the HP pump this relay should have its own supply direct from the battery and its own fuse.
Do you know what current the HP pump is going to draw? This will determine the size of relay, cable and fuse.

Steve

the hp pump needs 25 amp max but at 43psi will draw about 16amps

[Steve_D]

Discopotatoes said:

Steve_D said:

Discopotatoes said:

Steve_D said:

Run separate relays and supply fuses. Fuses are there to protect the wiring. The wiring and fuse for the HP pump will be much heavier than the LP pump so if you run them together the large fuse (for the HP) will not protect the smaller wiring of the LP. Run both relays signalled by the ECU.

On the plumbing side the HP pumps have a tendency to cavitate at the inlet port particularly if the pump is not lower than, and close too, the swirl pot. This may not be quite as relevant with a submerged pump but what I'm going to suggest is still valid.
The LP (Red Top) pump fills the swirl pot and un-used fuel is returned to the tank but this does not need to happen. The only reason for the return pipe is to let any trapped air or vapour to escape from the swirl pot and return to the tank. If you put a restriction in the return pipe the LP pump will maintain a pressure in the tank which will help prevent cavitation at the HP Pump. The LP pump is internally regulated at around 7psi so there is no issue with restricting the flow as this is pretty much what happens when that pump is feeding a carb with a full float chamber.

Steve

still trying to get my head around this wiring.
if the fuse is there to protect the wiring loom, can i use the original wiring and fuse for the lift pump then wire the hp pump of the same relay and fuse?

Yes use all the existing wiring to now run your LP pump but use the same signal from the ECU to trip a new heavy duty relay for the HP pump this relay should have its own supply direct from the battery and its own fuse.
Do you know what current the HP pump is going to draw? This will determine the size of relay, cable and fuse.

Steve

the hp pump needs 25 amp max but at 43psi will draw about 16amps

So a 40 amp relay will work fine and for best results use as heavy a gauge of wire on the supply and output as you sensibly can particularly if the cable run is long as volt drop will not help your cause.

Steve