Auxiliary fuel pump sequence of operations question

[MajorGasAttak]

Am I correct in my observation that the auxiliary fuel pump runs continuously when the selector switch is in the aux position but that the auxiliary fuel solenoid opens and closes as needed to top off the onboard day tank? At least that's how mine seems to be working.

Thanks

 

[Carl_in_NH]

You don't mention which genset you've got, but generally speaking, yes - that's how the AUX system works; it runs the AUX pump to top off the day tank until the float switch in the day tank reports it's full. Then when the float switch drops below a pre-determined level it enables the AUX pump again to refill the day tank.

 

[MajorGasAttak]

My apologies. I have an MEP-003a. It's just odd that the pump remains energized even when the float switch is satisfied and the solenoid valve is closed.

 

[steelypip]

If it makes you feel any better, I thought the float switch on my MEP-002A was broken when I got it for the same reason. Careful examination of the plumbing and wiring diagrams clued me in...

 

[SteveH]

If it makes you feel any better, I thought the float switch on my MEP-002A was broken when I got it for the same reason. Careful examination of the plumbing and wiring diagrams clued me in...

I've noticed something similar with the main fuel pumps (E2 and E3). When the switch is in a 'RUN' position they are permanently energized (I'm looking at the electrical schematics). I'm surprised at this - wouldn't it mean that if the unit ran out of fuel or stopped running for some other reason, the pumps would burn out (or kill the battery). I'm also concerned that a major fuel leak (burst hose) that killed the unit would leave the pumps running....

Note - I posted about this in my PLC Autostart thread, but just noticed your thread - apologies for the duplication

 

[Triple Jim]

The way the pumps are designed, they energize their solenoids only when the pressure drops enough for the plunger to return to its relaxed position. When the flow is restricted, they slow way down and don't draw a lot of current. If they get full of air from an empty tank, they go nuts trying to refill themselves, but I've never seen one damaged from this.

If my MEP-003A stopped running, I'd go out and turn everything off. For an unattended automated setup, you're making a good point to install a main 24V contactor and program the PLC to automatically disconnect the 24V power if the engine stops.