Your last generator Maintenance Run

[LouNY]

The electricity actually comes from the negative side in a DC system, not the hot or positive side. Electrons have negative charge, so the side showing negative has all the extra electrons that will go rushing towards the positive side.

That depends on whether you go with hole theory or electron theory :drink:

 

[Chilliwack Murray]

In the case of switching, the current is the same throughout a circuit regardless of where the voltage drop is (where the energy is consumed) so it makes no difference where you break it. When current is flowing in a circuit there is low voltage to ground on the neutral (or negative on a negative ground) making it safer to handle however as soon as the circuit is interrupted there is full voltage across the open switch contact. There is no difference if you break the hot and measure across the open switch on the hot side.

As for inrush current on a motor, it’s typically 6-8 times the running current but shouldn’t last more than 6 cycles or 100ms. If you are sure the controller is tripping at 300 amps and there is an adequate delay to override the inrush you most likely have a failing or failed starting capacitor on the motor.

One other thought, many new controls include a “maintenance mode” or “reduced energy level trip” which reduces the short circuit threshold significantly reducing the arc flash hazard for workers. Many controls enter this mode when run manually since the assumption is there is someone near the unit. You may need to disable this feature.

 

[Industrial Toys]

Murray. Do you ever work on the little Quiet Diesels? I am having issues with a 7.5 not holding it's (fuel) prime. A friend says the pumps are to blame, but I am not convinced. I notice that I can rotate the hose on the banjoe fitting to the injector pump and the hose to the internal filter and pump may be the same. They have a crimped on hose clamp. Any thoughts? Thanks

 

[Chilliwack Murray]

I haven’t worked on those smaller units in about 12 years but like any inline pump they can be prone to leak down for a few different reasons. The most common sources of drainback on gensets are flare fittings either scratched/damaged or that have Teflon applied to them or leaks from filters with damaged o-rings or not tightened to spec.

Not sure if you are dealing with a Kubota or Isuzu powered unit but both will have a return check valve on the pump body that is responsible for maintaining a fixed pressure in the pump body thereby determining the amount of fuel metered into the plungers still a given opening.

If this check valve doesn’t seat when the unit is not running the pump body can bleed down if the return line is open ended. As a general rule, in-line pump plunger fuel systems should have the return line terminating below the fuel level in the tank. This will prevent siphoning since the weight of the fuel in the supply line is counteracted by the weight of the fuel in the return. Kubotas also have a thumbscrew on the pump outlet for bleeding that should remain closed at all other times.

If there is an electric lift pump is it certainly possible for it to develop a leak under vacuum just as a mechanical lift pump can.

The best test for a fuel supply system is a hand vacuum pump. Seal the pickup and pump a vacuum on the system and see if it holds a moderate vacuum. Or on a larger system with a decent amount of lift pull fuel up a clear line and wait to see if bubbles appear. If so, you can localize the test to see where the source is.
.

 

[Industrial Toys]

Thanks. It has an electric lift pump. Maybe I designed the fuel system all wrong external to the generator. Three foot high tank with suction tube coming off top, going down to a Racor Filter/Water seperator down low, and then to the generator fuel input, which is right into the electric pump, to their fuel filter and to the Banjoe fitting on the injector pump. Return line goes to the top of my tank.



I just got a fittting so my intention was to take the fuel fitting off the top of the tank and pressurize it via a regulator. See what leaks. Probably suction leaks and pressure leaks could be different.

 

[3930dave]

Master class in Fuel Systems....... thanks to the internets, and cm ! :thumbsup:

I do like learning about all these systems (really), but, after a long tiring week, my mind drifted to thinking "I can see why something like a Lister is still common in the 3rd World.....".

Some of the issues cm listed on this page won't always quickly/accurately get sorted in the First World.....

Rgds, D

 

[Chilliwack Murray]

That setup looks pretty much by the book. I wouldn’t change it. A drop tube on the return is recommended but lack of one rarely causes issues.

With your design the only place it could drain back is the high point at the top of the tank emptying the drop tube.

You didn’t mention what the drain back symptoms are... Does it not fire at all
suggesting the injection pump is losing prime or does it start and die suggesting air in the lines or filter being pulled in after it starts?

Vacuum is a better test as some leaks will not appear under pressure. It’s also possible to have a very small leak that allows air to collect and eventually build up until it all goes through at once... often on startup when there’s a surge of flow.

 

[Industrial Toys]

Thanks. Great information as usual.

I have a vaccume pump but no gauge. Never tried using it for anything.

Even with the supply valve having been closed at the top of the fuel tank, the machine cranks but does not attempt to fire. After a second of priming, you can hear the pump suddenly get fuel, but this does not make it start the engine. Bleeding fuel at the injector pump allows a fairly fast start, otherwise just a lot of cranking. Priming alone, (holding switch in OFF position) does not in itself solve the problem.

 

[Chilliwack Murray]

Have you confirmed the fuel rack is actually moving when you are first trying to start it?

Maybe a sticking plunger or actuator is just taking a little time to free up.

A vacuum gauge isn’t critical for finding air, clear tube so you can see bubbles it’s the best.

 

[Industrial Toys]

Well, as usual, I think the problem was of my own making. I pressurized the system just after my pickup tube and valve, and not a drop anywhere. I tried taking fuel off the water drain at the bottom of the filter which "should" siphone fuel out of the tank as this is lower than the 1/4 or so level of the tank. No-Go. I think I had a problem with the SECOND valve I have tried. The threads don't appear to be NPT and I think were leaking. Put in a nipple and pipe compound (for oil) and I "THINK" I might have solved my problem. I had left the battery connected for days, so I have to charge it before further testing can be done.

Curious where I can get a 1/4" ball valve that won't give me grief for fuel suction applications. Also, do you need to lube fuel filter 'O' rings prior to use? I also wonder if a 1/4" copper pick up tube is a bit large and easy to loose prime.

I am glad, that I never filled the tank, as possibly these issues would not have come to light until the tank level went down.