Need a Fuel Tank Selector Valve

[hatzie]

I'd give the pair of FV-1 valves a shot.

I drew up a schematic several years ago for installing the motorized valve with a minimum disruption to the original wiring.
It uses a pair of 5 terminal Mini ISO relays to convert the un-molested single wire setup to a motorized valve 2 wire system without modifying the dash switch or in-cab harness.
It's not a beginner wiring project.
You'd need to properly wire up 2 relay sockets and two tower terminals on the 6 position Delphi Weatherpack connector.
I'd recommend mounting relays on the firewall with the terminals down. The reason to mount relays with the terminals pointing toward the ground is... they fill with water in any other position and then stop working.
The main power connection should be to t̶h̶e̶ ̶f̶i̶r̶e̶w̶a̶l̶l̶ ̶j̶u̶n̶c̶t̶i̶o̶n̶ ̶s̶t̶u̶d̶ an ignition switched power source. It should include a 7amp Fuse.

[rajincajintj]

Originally Posted by hatzie

I'd give the pair of FV-1 valves a shot.

I drew up a schematic several years ago for installing the motorized valve with a minimum disruption to the original wiring.
It uses a pair of 5 terminal Mini ISO relays to convert the un-molested single wire setup to a motorized valve 2 wire system without modifying the dash switch or in-cab harness.
It's not a beginner wiring project.
You'd need to properly wire up 2 relay sockets and two tower terminals on the 6 position Delphi Weatherpack connector.
I'd recommend mounting relays on the firewall with the terminals down. The reason to mount relays with the terminals pointing toward the ground is... they fill with water in any other position and then stop working.
The main power connection should be to the firewall junction stud and it should include a 7amp Fuse.

thanks for that information. i really do not like the idea of 2 singular pumps. when i started out the journey, i made a commitment to the truck. if i could not replace like in kind, i would upgrade. sounds like i need to honor that.

[hatzie]

Originally Posted by rajincajintj

thanks for that information. i really do not like the idea of 2 singular pumps. when i started out the journey, i made a commitment to the truck. if i could not replace like in kind, i would upgrade. sounds like i need to honor that.

I'd like to take back my comment about hooking to the firewall stud. I'd hook the 12v+ power connection in the diagram to an ignition switched 12v+ source. I modified the drawing to reflect this.

Why? You want to run the valve as little as possible. If the source is the battery and the valve is in the AUX position it'll cycle when you turn the truck on and off.

[rajincajintj]

Originally Posted by hatzie

I'd like to take back my comment about hooking to the firewall stud. I'd hook the 12v+ power connection in the diagram to an ignition switched 12v+ source. I modified the drawing to reflect this.

Why? You want to run the valve as little as possible. If the source is the battery and the valve is in the AUX position it'll cycle when you turn the truck on and off.

hatzie,

please dont take this the wrong way, but i don't follow you here. i would think you need a constant power source to keep the switching and operating of the valve to a minimum. if your 12 volt source is constantly going high and low (as the ignition does) wouldn't it cycle the valve every time the ignition turned on when the D wire has +12V power?

if you keep the +12V source constant, the relays and valve only cycle when the switch is turned, right?

i might be reading your schematic wrong and i definitely dont mean to poke holes in your suggestions, i just want to be clear on the purpose.
thank you for your support in this, man. you are already saving me potentially hours of under truck time.

[hatzie]

The motorized valve is very different from the solenoid valve.
The motorized valve shuttle is moved by a DC micro motor that only moves when the control polarity on terminals D & E changes. The valve incorporates an internal limit switch with diodes. The limit switch cuts power to the motor once the valve shuttle has reached the end of it's travel. It retains its' position till the control polarity on terminals D & E is reversed.

Micro ISO relays have an energized and rest position for the internal switch. They don't retain their switched position without power to the coil + terminal #86.
The dash switch is on ignition power so the relays in my diagram will go to the rest position when the ignition is switched off.
If there's power present on the Red +12v wire in the diagram the valve will spin to the MAIN position just as if you flipped the dash switch to MAIN.

I've been intending to do a tech writeup on the two tank switchover systems on the 73-91 CK RV trucks...
Here's a couple graphics from that incomplete effort that may help you visualize what's happening in the motor type valve.

Here's a cutaway of the motorized valve from Pollack.


Internal Switches in Motorized Valve

[rajincajintj]

Originally Posted by hatzie

The dash switch is on ignition power so the relays in my diagram will go to the rest position when the ignition is switched off.

the devil is in the details. this make sense now.

thank you once again. i will do my best to write up how i make the upgrade.

[wilkin250r]

That's pretty close to how I would have done it, but it might be easier to replace the pair of relays with a single DPDT relay.

In any situation, you're running an additional wire to the valve. Whether you change the switch on the dashboard to the style designed specifically for the motorized valve, or you run relays under the dashboard and run power, you're STILL running an additional wire, you can't do it with just the single wire.




On a side note, just because it's an interesting project, I think I've found a way to run the motorized valve with just a single wire, but it would involve a power module (about $20) and a relay, not too much different than a pair of relays.

[hatzie]

Originally Posted by wilkin250r

That's pretty close to how I would have done it, but it might be easier to replace the pair of relays with a single DPDT relay.

In any situation, you're running an additional wire to the valve. Whether you change the switch on the dashboard to the style designed specifically for the motorized valve, or you run relays under the dashboard and run power, you're STILL running an additional wire, you can't do it with just the single wire.




On a side note, just because it's an interesting project, I think I've found a way to run the motorized valve with just a single wire, but it would involve a power module (about $20) and a relay, not too much different than a pair of relays.

I was wanted something that was frighteningly easy to service and so common you could get replacements bubble wrapped at WalMart or any big-box auto parts store.

The Micro ISO SPDT relay, in its' many incarnations, has been around for over 4 decades. It's still being used in brand new industrial applications... literally thousands at a time. You can find em in late 1960's VWs and they've used them by the thousands in transit coaches... Open the overhead electrical compartment on a 2004 Nova LFS transit coach. There's literally two 3' x 4' hinged panels of 12v & 24v Mini ISO relays. Even the "modern" automobile, truck, and transit coach designs still use Mini ISO relays in several places where the current load would kill the modern PLC. It's probably going to stay available for a very long time.

I actually thought about using a T-92 DPDT Automotive grade relay but they are simply not as common. They don't have foolproof sockets with mounting tabs either so R&R is more complicated. They are not commonly used in industry so the supply will dry up and blow away. The DPDT relays with mounting sockets that you can find at Radio Snack are simply not robust enough to survive an automotive environment. The footprint of both the T-92 and the clear case relays is larger than the Mini ISO relays with the Lego sockets. At least that was my thinking.......

I'm interested to see what you've come up with using a single wire.
It's fairly entertaining, to me, to see other folks ways to replace obsolete electrical parts without super intrusive and difficult to reverse modifications. I've played that game with Nixie tube driver chips on my Ham-Fest Frequency counter. I eventually found a NOS tube of the correct driver chips and reversed my mod. The gods of electronics and computers Georg Ohm, James Watt, Charles Babbage, and Blaise Pascal were smiling on me when I picked that tube of brand new long obsolete chips out of a bucket and paid $3 for it.
Durn engineers.

[wilkin250r]

The single-wire approach is fairly simple in concept, but slightly more difficult to put into practice.

In theory, a simple buck/boost converter module to produce a -12V from a +12V power, then a relay to switch your single wire between +12V and -12V would essentially be the same as reversing polarity.

I can find pre-made DC-DC converter modules easily, many less than $5, and not much bigger than a relay. But to work, it either needs to offer full isolation, or it needs to specifically invert the source voltage. These aspects are simple enough design if I was doing the circuit from scratch, but very rare to find in a pre-made module. I've found a couple in the realm of $100, but nothing on the realm of $8.

[hatzie]

The only problem with that is the valve has diodes in the limit switch assembly. You actually have to make the ground wire hot and the hot wire ground or no electrons pass the diode. It doesn't matter if you have +12v or -12v the diode blocks the electron flow.

[wilkin250r]

Only if the motor and diodes also tie to chassis ground through the valve housing (and I doubt that is the case) you could get a ground short.

But if that portion of the circuit is isolated and the only path to ground is made through the selector switch on the dash, then it doesn't matter which wire is "ground". It only matters that one wire is 12V different than the other. It's irrelevant whether you go +12V down to zero, or you go from zero down to -12V, there is still +12V difference.

[hatzie]

Will the resistance of the motor affect the ground reference point for your power supply outputs?

[wilkin250r]

No, it would be a fairly well-regulated DC-DC converter. The only thing I would need to measure is the current draw of the motor. A 5W power module is significantly cheaper than a 15W module.

Honestly, though, of all the suggestions I have seen, I think the first one I would try would be the dual FV1 valves, and not just because it was my suggestion. It really looks to be the most simple, straightfoward fix, requiring nothing more than an extra valve and some minor routing of hoses.

True, it doubles your chance of failure, but the failure rate is already very low to begin with. If the average lifespan of a valve is 20 years, now you're theoretically at 10 years. I can live with that kind of risk.

[78trk]

I have a 78 with 2 tanks. I used a switch and wiring connector for a 81-87 w/carb. from Chevrolet. The after market switches seem to come apart to easy. Enlarge the hole for newer style switch and add a ground wire to switch.
I used a 81-87 6 port fuel tank switch.
I used the existing hot wire to the input of the old switch and that switched one tank on the fuel tank valve and I added another wire to the output of the switch to switch the other tank on the valve.
I attached the gas tank sensor wires to the fuel tank valve.
The new momentary fuel tank valve is a much better valve and after the dash switch switches tanks it shuts off power to the valve.

[hatzie]

Originally Posted by 78trk

I have a 78 with 2 tanks. I used a switch and wiring connector for a 81-87 w/carb. from Chevrolet. The after market switches seem to come apart to easy. Enlarge the hole for newer style switch and add a ground wire to switch.
I used a 81-87 6 port fuel tank switch.
I used the existing hot wire to the input of the old switch and that switched one tank on the fuel tank valve and I added another wire to the output of the switch to switch the other tank on the valve.
I attached the gas tank sensor wires to the fuel tank valve.
The new momentary fuel tank valve is a much better valve and after the dash switch switches tanks it shuts off power to the valve.

The Delco Momentary rocker switch is a pain in the neck and there's no reason for it. Use a maintained state switch. The valve shuts off power to itself using diodes on the internal limit switch.
Cole Hersee makes an excellent quality polarity reversing toggle switch. http://www.colehersee.com/home/item/cat/52/55018-01/
It's far more robust than the 81-86 or 87-91 AC Delco polarity reversing rockers. You could re-use the 74-80 switch connector on it, that's actually still produced, instead of searching for the long obsolete 81-91 switch connector. A toggle will mount like Ray did at the bottom of the lip on the dash.

One could keep the rocker for the gauge and put the valve toggle right next to it. It would allow a check of fuel levels without swapping the run tank.

There are lots of ways to do this. The relay arrangement was me staying away from heavy modifications to the existing harness.

[rajincajintj]

Half way there. I'm still undecided on where to mount these relays. The more I thing about it, the more I want them on the frame rail and not under the hood. I Would like to use some sort of weatherproof box but I can't find one I like yet. It's probably time to start a new thread

[hatzie]

If they're not going in the engine bay put em under the dash.

[rajincajintj]

Originally Posted by hatzie

If they're not going in the engine bay put em under the dash.

I was thinking something like this next to the valve on the frame rail



I'd like to keep the under dash as clean and stock as possible.