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While working on an other unrelated topic (Retrofitting 005A with MeBay Controller DC70DR MKII, see separate thread), Larry ( @Cowhunter ) encountered some problems with his fuel delivery system. Looking from a retrospect, this issue must have existed for quite sometime and from a time prior to Larry acquiring this Genset a few years ago.
I have not come across any previous threads describing a repair of this Fuel Level Switch, but such a thread may exist here in this forum and I am sure Guy ( @Guyfang ) could write a book about this Switch assembly.
Anyway, here is a short explanation of what happened, what we found and how we proceeded:
The issue at hand was a Day Tank which had randomly ran dry, requiring the Start Switch to be placed in run and Battle Short active to prime system and fill Day Tank, then came the task of getting the air out of the IP System.
After Checking Day Tank Solenoid, Fuel pumps and Fuel Cut Off Solenoid, we discovered the source, the Fuel Level Switch.
The Fuel Level Switch is rather a assembly of two normally open reed contacts (switch), labeled in the TM's as FO-1 / FL-1 and FO-2 / FL-2
The two floats contain small round magnets and when at a particular height, depending on the fuel level, close the two contacts in the reed switch through their magnetic field.
Fuel Level Switch marked as # 16 original NSN 2910-00-405-6153 ( with move able float stops ) and the later version NSN 5930-00-405-6153 ( with fixed float stops )
Shown here NSN 5930-00-405-6153 ( with fixed float stops [ 4x C-Clips ] ) from a eBay listing
The original NSN 2910-00-405-6153 ( with move able float stops )
This is the Fuel Level Switch Larry has in its Day Tank
The lower float turns on Reed Switch FL-1 which then activates K8, shuts down running Genset and triggers the Fault Indicator Panel, or so is the theroy
The upper float when in the low position turns on FL-2 which then activates the Day Tank Solenoid through the Half Bridge Rectifier CR 27 and keeps this Solenoid active until float has risen through increased fuel level in tank to its top position at which point Solenoid is turned off. At least, so is the theory.
The actual stop points / limits for each float is adjustable by loosening the set screws on the threaded move able brass stop's.
The upper float to keep day tank at certain variable fuel level has 4 small round magnets. In our case here, they are on the top side ( non ring side ) of this float.
The lower float has two magnets also on the top side ( non ring side ) of this float.
As you can see, the middle and upper stops also have a additional steel ring with a setscrew, which when loosened, allows for adjustment of this steel ring without changing the stop position.
These rings serve, in conjunction with the 4 magnets, the purpose of delaying the movement of the upper float to add additional time for Solenoid to be active, providing a slight overfill over the top of the float at stop position.
However, some Genius had installed the top float upside down, as the 4 magnets should attache the float magnetically to the center stop. The release force, which increases with rising fuel level, can be adjusted by rotating the steel ring up or down on the threaded part of the respective stop and is secured in place by means of the setscrew on steel ring.
In our case, the magnets where holding the float to the top stop, which turns FL-2 off, not allowing therefor for FL-2 to close and activate the Day Tank Solenoid.
Normally the lower Switch, FL-1 should then eventually shut off Genset when the level in day tank is low enough, but not completely empty.
The lower switch FL-1 does not utilize the magnetic delay of action since it has only two magnets. It is allowed to move freely in real time with actual fuel level.
And this is where it got tricky. FL-1 would either turn on constantly or not at all, allowing Day Tank to be drained completely without stopping a running Genset.
We therefor proceeded to take the entire assembly apart:
We can now clearly see the two reed switches after Larry cleaned the old coating off with MEK and scraped out the outer brass tube from the broken down, gummy silicone rubber filling.
The lower switch is FL-1 and has two black wires connected, which connect to PIN C and D on socket. The upper switch is FL-2 and has two white wires connected, which connect to Pin A and B on socket.
We can also clearly see the bare wire on the lower connection.
Because of the age of this device ( 40 to 50 years old ), the internal Silicone Rubber filling had broken down and this end was making intermittent contact with the outer brass tube, causing the K8 not turn on.
These are the detail pictures of the two switches
FL-1 ( Low Fuel Shut Down )
FL-2 ( Day Tank Fill )
Note: both contacts are open even though the appear to be closed / making contact
After carefully inspecting and testing everything, Larry used 3/8" 2:1 Shrink Tubing with no glue to reassemble the Switch assembly
We then adjusted float stops and made sure top float had the 4 magnets on the bottom side of float.
Now the Day Tank system is working correctly again with the MeBay Controller.
Note: we left the Day Tank Solenoid Circuitry as it was originally, only applying 24V thorough our Fuel Relay ( see Mebay Thread )
I have not come across any previous threads describing a repair of this Fuel Level Switch, but such a thread may exist here in this forum and I am sure Guy ( @Guyfang ) could write a book about this Switch assembly.
Anyway, here is a short explanation of what happened, what we found and how we proceeded:
The issue at hand was a Day Tank which had randomly ran dry, requiring the Start Switch to be placed in run and Battle Short active to prime system and fill Day Tank, then came the task of getting the air out of the IP System.
After Checking Day Tank Solenoid, Fuel pumps and Fuel Cut Off Solenoid, we discovered the source, the Fuel Level Switch.
The Fuel Level Switch is rather a assembly of two normally open reed contacts (switch), labeled in the TM's as FO-1 / FL-1 and FO-2 / FL-2
The two floats contain small round magnets and when at a particular height, depending on the fuel level, close the two contacts in the reed switch through their magnetic field.
Fuel Level Switch marked as # 16 original NSN 2910-00-405-6153 ( with move able float stops ) and the later version NSN 5930-00-405-6153 ( with fixed float stops )
Shown here NSN 5930-00-405-6153 ( with fixed float stops [ 4x C-Clips ] ) from a eBay listing
The original NSN 2910-00-405-6153 ( with move able float stops )
This is the Fuel Level Switch Larry has in its Day Tank
The lower float turns on Reed Switch FL-1 which then activates K8, shuts down running Genset and triggers the Fault Indicator Panel, or so is the theroy
The upper float when in the low position turns on FL-2 which then activates the Day Tank Solenoid through the Half Bridge Rectifier CR 27 and keeps this Solenoid active until float has risen through increased fuel level in tank to its top position at which point Solenoid is turned off. At least, so is the theory.
The actual stop points / limits for each float is adjustable by loosening the set screws on the threaded move able brass stop's.
The upper float to keep day tank at certain variable fuel level has 4 small round magnets. In our case here, they are on the top side ( non ring side ) of this float.
The lower float has two magnets also on the top side ( non ring side ) of this float.
As you can see, the middle and upper stops also have a additional steel ring with a setscrew, which when loosened, allows for adjustment of this steel ring without changing the stop position.
These rings serve, in conjunction with the 4 magnets, the purpose of delaying the movement of the upper float to add additional time for Solenoid to be active, providing a slight overfill over the top of the float at stop position.
However, some Genius had installed the top float upside down, as the 4 magnets should attache the float magnetically to the center stop. The release force, which increases with rising fuel level, can be adjusted by rotating the steel ring up or down on the threaded part of the respective stop and is secured in place by means of the setscrew on steel ring.
In our case, the magnets where holding the float to the top stop, which turns FL-2 off, not allowing therefor for FL-2 to close and activate the Day Tank Solenoid.
Normally the lower Switch, FL-1 should then eventually shut off Genset when the level in day tank is low enough, but not completely empty.
The lower switch FL-1 does not utilize the magnetic delay of action since it has only two magnets. It is allowed to move freely in real time with actual fuel level.
And this is where it got tricky. FL-1 would either turn on constantly or not at all, allowing Day Tank to be drained completely without stopping a running Genset.
We therefor proceeded to take the entire assembly apart:
We can now clearly see the two reed switches after Larry cleaned the old coating off with MEK and scraped out the outer brass tube from the broken down, gummy silicone rubber filling.
The lower switch is FL-1 and has two black wires connected, which connect to PIN C and D on socket. The upper switch is FL-2 and has two white wires connected, which connect to Pin A and B on socket.
We can also clearly see the bare wire on the lower connection.
Because of the age of this device ( 40 to 50 years old ), the internal Silicone Rubber filling had broken down and this end was making intermittent contact with the outer brass tube, causing the K8 not turn on.
These are the detail pictures of the two switches
FL-1 ( Low Fuel Shut Down )
FL-2 ( Day Tank Fill )
Note: both contacts are open even though the appear to be closed / making contact
After carefully inspecting and testing everything, Larry used 3/8" 2:1 Shrink Tubing with no glue to reassemble the Switch assembly
We then adjusted float stops and made sure top float had the 4 magnets on the bottom side of float.
Now the Day Tank system is working correctly again with the MeBay Controller.
Note: we left the Day Tank Solenoid Circuitry as it was originally, only applying 24V thorough our Fuel Relay ( see Mebay Thread )
