1972 Fuel Transfer Valve

[Brian 72 K20]

I have an Imperial gas valve installed under the driver's seat. The lever in the pax compartment looks similar to the assembly manual, but it seems to be a valve for two auxiliary tanks. It has one 3/8 inch hose coming from the main tank and two smaller 1/4 inch hoses going to each side of the vehicle. These have ferule type fittings. The lever has "Imperial" on it. It just freely turns and doesn't seem to "click" in any position. Is this a stock set up or something a previous owner installed?

[Stocker]

Not stock -- it appears similar to my aftermarket valve (I have the stock tank behind the seat, and twin saddle tanks). As you say, it looks like a setup for 2 auxiliary tanks and the main tank. But since it turns freely and doesn't 'click', it may be defective. Mine takes effort to turn, and it clicks at every 90-degree position.

[Brian 72 K20]

Thanks. I think I'll take it out.

Where'd you find the saddle tanks?

[Orange Crate]

Could be an NL2 aux tank. Check your SPID.

[Stocker]

Originally Posted by Brian 72 K20

Thanks. I think I'll take it out.

Where'd you find the saddle tanks?

When I bought my K20 in 1977, a PO had already installed the saddle tanks. They were made by a company called Travel Tanks, and they went out of business several years ago.

[Brian 72 K20]

thanks

[PbFut]

NL2 option is a single tank on driver side. Any passenger side tank was aftermarket. Note your valve does not switch a return line. Not a particular issue but be sure to drain main tank first so you have room for return fuel. Common for aftermarket setups

[Brian 72 K20]

Originally Posted by PbFut

NL2 option is a single tank on driver side. Any passenger side tank was aftermarket. Note your valve does not switch a return line. Not a particular issue but be sure to drain main tank first so you have room for return fuel. Common for aftermarket setups

Do you mean when I'm using the aux tank, the fuel will flow back into the main tank? What's the return line do?

[PbFut]

The return line is on later (I don't know for sure, may have started in 1970) fuel pumps. The return line was a regulator allowing surplus pumped fuel a way to return back to the fuel tank. It helped with vapor lock and likely provided a more reliable pressure regulation method for carburetor supply between pump and carb. The valve you have only directs the supply fuel. Left, right and main tank is the upper 3, and the center elbowed nipple goes to the fuel pump. If your truck has the return style pump, that line is directed back to the main tank and has no provision to return to either of the auxiliary tanks. Say you fill all 3 tanks. If you start drawing from an aux tank, the return fuel will overfill the main tank and you will have fuel pushing out the gas cap. So you start drawing from the main tank. When low, switch to 1 aux tank. You will actually see the main tank gauge come up as the return fuel is pushed to the main. Draw the main tank down again, then switch to the 2nd aux tank a repeat. It was sort of a pain to deal with, but better than stopping every 175 miles or so. I corrected using 2 modern electric valves. A good 3 tank selector valve with return line ability is very pricey. The modern electric valves available on amazon Controls...Supply, return, pump power if intank, and sender signal. So with one flip of a switch all points are covered and no out of sync gauges or return lines. I did a post on it a while back detailing the setup. It's involved but nice to use when complete. There were a few of us messing with the aux tanks about 3 years ago. Lots of posts on the subject then it quieted down as we all got things completed. Remember, old fuel tanks are dangerous. The vapers inside can last for years and create a large bomb.

[Stocker]

FWIW, my '72 K20 is a mechanically stock, original California truck (Fremont plant). It does not have a fuel return line. Fuel pump has two connections -- gas in, gas out.

[Brian 72 K20]

very good to know. thanks

[57taskforce]

Originally Posted by PbFut

The return line is on later (I don't know for sure, may have started in 1970) fuel pumps. The return line was a regulator allowing surplus pumped fuel a way to return back to the fuel tank. It helped with vapor lock and likely provided a more reliable pressure regulation method for carburetor supply between pump and carb. The valve you have only directs the supply fuel. Left, right and main tank is the upper 3, and the center elbowed nipple goes to the fuel pump. If your truck has the return style pump, that line is directed back to the main tank and has no provision to return to either of the auxiliary tanks. Say you fill all 3 tanks. If you start drawing from an aux tank, the return fuel will overfill the main tank and you will have fuel pushing out the gas cap. So you start drawing from the main tank. When low, switch to 1 aux tank. You will actually see the main tank gauge come up as the return fuel is pushed to the main. Draw the main tank down again, then switch to the 2nd aux tank a repeat. It was sort of a pain to deal with, but better than stopping every 175 miles or so. I corrected using 2 modern electric valves. A good 3 tank selector valve with return line ability is very pricey. The modern electric valves available on amazon Controls...Supply, return, pump power if intank, and sender signal. So with one flip of a switch all points are covered and no out of sync gauges or return lines. I did a post on it a while back detailing the setup. It's involved but nice to use when complete. There were a few of us messing with the aux tanks about 3 years ago. Lots of posts on the subject then it quieted down as we all got things completed. Remember, old fuel tanks are dangerous. The vapers inside can last for years and create a large bomb.

The return line is part of the eec/emissions package that some of the 1/2 ton trucks had. A K20 doesn’t have any of it. As stocker said it just uses an in/out pump.

[PbFut]

Interesting on the return line. I have a Fremont build Ca delivered gmc 3/4 ton. Commercial classification. No ecc venting but does have return lines. The factory NL2 option aux tank was plumbed with a stacked selector valve that did route supply and return fuel and had factory hard lines in place for both tanks.
30 years ago I owned a 1971 c20. It had 3 tanks not NL2 optioned and return line only to main tank. I had to do the flip flop method on that truck.