Can Not Solve This Mystery

[NCMau]

I have a gas caddy with a 20 GPM pump and a 3/4" hose. For some reasons I can not get an automatic shutoff nozzle to work (no flow). The last one I ordered specifically stated that it was designed to work with a minimum of 13 GPM. The first two I wasn't sure. I asked the suppliers and they said it should work. I returned both of them. This 13 GPM nozzle should work with my system, but it is not. After three nozzles tries, I don't have a clue on what it could be. My standard non-automatic works great and I am getting the full pump flow.
There is nothing adjustable in the auto shutoff nozzle that I am aware. If somebody has any idea, please chime in. I am all ears.

 

[Industrial Toys]

I just have issues with the auto-nozzles shutting off from the air escaping the tank as you fill. I am guessing aside from the detection system and it tripping off the hold-on catch that there is nothing different about the nozzle. Just a valve. If you hold open the handle, you should be able to blow through it.

 

[Scooby074]

Are you actually getting the full 20gpm at the end of the nozzle? Test actual output using a 5gal bucket and a stopwatch

 

[NCMau]

Are you actually getting the full 20gpm at the end of the nozzle? Test actual output using a 5gal bucket and a stopwatch

Yes, I did the 5 gal can test.

 

[crazyal]

Does it start then click off like the tank is full or does it just do nothing? The way the automatic nozzles work is that there is a small tube inside the nozzle. As fuel comes out it creates a vacuum in the small tube, the venturi effect. Once the fuel in the tank reaches the small tube the vacuum is lost and the fuel is shut off. If you've ever had a car that is impossible to fill because the nozzle keeps shutting off it's usually because of the shape of the pipe going to the tank. Fuel could be splashing back onto the small inner tube. Also when you fill a tank the air inside the tank is trying to escape and could be disrupting the vacuum needed to keep the nozzle's valve open. The nozzle needs to flow a bit of gas to get the vacuum to form. If your flow doesn't start quick enough and isn't fast enough a vacuum wont be formed. I would to make sure you don't have air in the hose. If your flow is on the edge of what's needed having air mixed in with the fuel could reduce how much vacuum could be formed. Another thing would be to try to fill more than one tank to make sure it's not the tank causing you issues.

 

[Redneck in training]

My guess is that it isn't the flow issue but pressure. The pump doesn't develop enough pressure to latch the valve to the lever that opens the valve. You need to prime the pump first. The pump also might have internal leakage or safety bypass set to too low pressure (if it has one) or it is sucking air in.

Pump Priming with Automatic Nozzle - Fill-Rite