Fuel Flow Rate Question for Trailer Onboard Fuel

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Dockmaster

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My 26' enclosed trailer has two 40 gallon fuel tanks. The tanks are mounted over the axles and the pump is mounted in a compartment at the front of the trailer. There are 1/2" typical fuel hoses running about 15' from the tanks to the pump. The pump is rated to pump 5 gal/min but I'm only getting a little under 2.5 gal/min. The auto shut off on the nozzle doesn't shut off and the theory is the flow is too low to activate the shut off. The discharge ports on the tanks are 1/2" and the input on the pump is also 1/2". My question is; if I increase the hose size between the tanks and pump will I get increased flow? Or will the flow still be restricted by the 1/2" fittings on the tanks and pump? The 1/2" hose takes a few ups/down as it clears main cross members. My thought was to install a straight run of 0.5" nominal aluminum tubing (0.622" I.D.) welded through the cross members and get it as close to the tank and pump as possible. Then use the 1/2" fittings as close to the tank and pump as I can reasonably get. I'm thinking by having a straight shot of tubing with a little larger I.D. the flow resistance should be pretty significantly reduced thereby increasing flow? Or would this all be a waste of time as the flow is still going to be what it is now due to the 1/2" sizes at the tank and pump. Surely the pump must be capable of more flow even with the 1/2" inlet or how could it be rated to 5 gpm?
 
I've always been told that pumps are better at pushing instead of pulling. Can you put the pump closer to the tank and just run a longer hose to the front? Assuming you prefer it at the front for refueling your car?
 
Pumps work best when they are close to the source. This may be a suction/vacuum issue. Another thought is venting of the tank. What size vent does each tank have? Have you tried dispensing fuel with the fill cap loosened or removed?
 
AlpineFunco said:
I've always been told that pumps are better at pushing instead of pulling. Can you put the pump closer to the tank and just run a longer hose to the front? Assuming you prefer it at the front for refueling your car?
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Relocating the pump would be a major PITA. There is a manifold to select which tank you draw from. Everything would have to be moved under the trailer. I would just live with the slow flow vs going to all that trouble honestly.
 
Grease Monkey said:
Pumps work best when they are close to the source. This may be a suction/vacuum issue. Another thought is venting of the tank. What size vent does each tank have? Have you tried dispensing fuel with the fill cap loosened or removed?
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I have not tried that but certainly easy enough to do. But I'm doubtful the venting is the issue. But I'll try it to rule that out. Thanks!
 
Dockmaster said:
I have not tried that but certainly easy enough to do. But I'm doubtful the venting is the issue. But I'll try it to rule that out. Thanks!
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Venting issues would be obvious as the fuel is being pumped and the flow rate decreases once the vacuum increases. Not sure if your 2.5 per min is right out the gate or slows to this once you've moved some fuel.

Hows the flow once the pump is on, fuel line is loaded, and you pull the handle on the nozzle? Decent burst of fuel??
 
Grease Monkey said:
Venting issues would be obvious as the fuel is being pumped and the flow rate decreases once the vacuum increases. Not sure if your 2.5 per min is right out the gate or slows to this once you've moved some fuel.

Hows the flow once the pump is on, fuel line is loaded, and you pull the handle on the nozzle? Decent burst of fuel??
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I would say the flow is pretty consistent once flowing. No burst of flow at the beginning. I filled a 5 gal jug right to the 5 gal line several times and timed it Seems like the flow stays about the same throughout.
 
Upgrading your supply side to the pump will help get as much fuel to the pump as possible and should help flow rate if the pump is in good working order. The old existing 1/2" supply side hose could be breaking down under vacuum and collapsing and starving the pump for fuel supply.
 
Meter Tech said:
Upgrading your supply side to the pump will help get as much fuel to the pump as possible and should help flow rate if the pump is in good working order. The old existing 1/2" supply side hose could be breaking down under vacuum and collapsing and starving the pump for fuel supply.
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It's a pretty new trailer so it shouldn't be breaking down yet. But I believe you are correct that the vacuum and resistance has to be restricting it. I guess I could test this by using some 3/4" hose temporarily before going to the trouble of installing the fixed tubing.
 
Dockmaster said:
It's a pretty new trailer so it shouldn't be breaking down yet. But I believe you are correct that the vacuum and resistance has to be restricting it. I guess I could test this by using some 3/4" hose temporarily before going to the trouble of installing the fixed tubing.
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I think the pumps are normally a 3/4" inlet / outlet ports so if there is a 1/2" supply side is cavitating the pump.
 
Are you sure the pump is working properly? What’s the voltage at the pump during operation?
You can connect a different source to the pump ( gas can with larger diameter hose) and see if you get the same result.
 
FOG said:
Are you sure the pump is working properly? What’s the voltage at the pump during operation?
You can connect a different source to the pump ( gas can with larger diameter hose) and see if you get the same result.
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I don't have any reason to believe it isn't working correctly but I can check the voltage. I can also use a gas can close to the pump to see if it makes a difference. That's a good idea - thanks!
 
I'd guess the 5GPM rating is with a shorter hose than you're using. What's the pump?
 
Rockwood said:
I'd guess the 5GPM rating is with a shorter hose than you're using. What's the pump?
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Correct, the 5 GPM will be exiting the pump under normal parameters, every foot of hose with cause friction loss etc.
Applies to the inlet as well and why it is suggested to keep the pump as close to the supply source as possible.
 
My company does a lot of refueling of heavy equipment. The pumps do not flow as advertised. I’d say you’re lucky to get 1/2 the flow rate.
 
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