INLINE FUEL/AIR SEPARATORS

Racor Fuel/Air Separator Gas & Diesel Model #LG100
Racor Fuel/Air Separator Gas Only Model #LG50
Attwood Fuel Vent Line Surge Protector Model #1675
Attwood P-Trap Fuel Surge Protector Model #1689
Inline Fuel/Air Separator Summary

Above: The units were easy to install if you have proper access to your vent line (an ABYC standard). Simply cut a small section out of the vent line, place the fuel/air separator in the direction indicated in the instructions and use hose clamps to secure it.

An inline fuel/air separator is a simple and inexpensive device that is installed directly into your tank’s overboard vent line. As the fuel tank gets full and frothy fuel surges up from the tank, a ball rises and cuts off the travel of fuel that would normally escape overboard via the vent. Some of these devices claim to help shut off automatic fuel nozzles when your tank is full. Although none of the devices tested had a special whistle integrated to indicate fuel level (a feature we really loved in a now discontinued product) there was still an audible difference in some of the units when the tank was near full.

Above: RACOR FUEL/AIR SEPARATOR for GAS OR DIESEL (Model #LG100)

RACOR FUEL/AIR SEPARATOR for GAS OR DIESEL (Model #LG100; retails for $109.99) At first, we balked at the size of the LG100 (about the size of an oblong grapefruit). It was the largest of the units tested and we had just enough clearance to install it. But once installed, it worked each and every time on our mock-up and our loaner boat. When the tank became full, it allowed the automatic shut-off on the nozzle to disengage in plenty of time without venting fuel over the side or causing backsplash from the deck fill—with not one spill! We feel that because of its large size, it acted like a reservoir, allowing for additional room for fuel expansion. The larger size of this unit also provided the opportunity for fuel to settle before returning it to the tank and giving the nozzle time to click off. It works well with either gasoline or diesel and was the only product in our testing line up that could be taken apart if necessary. For these reasons, the Racor LG100 was the STAFF PICK for Foundation Findings #40. It can be ordered through BoatU.S. and West Marine stores, internet and catalog sales.

Above: RACOR FUEL/AIR SEPARATOR for GAS ONLY (Model #LG50)

RACOR FUEL/AIR SEPARATOR for GAS ONLY (Model #LG50; retails for $92.99). The Racor LG50 is the smaller, gasoline-only version of the Racor LG100 and is about the size of a large salt shaker. It functions the same way: a ball rises within the housing, preventing vented fuel from exiting the tank. However, this unit did not work as well as its bigger brother. It could not be disassembled, so we couldn’t tell exactly what was going on, but we surmised that the ball would float up as designed but would block the fuel and air too rapidly. This sudden shut off of fuel and air to the overboard vent surprised us when it caused backsplash through the deck fill, even when filling at the slower speed of 10 gpm. For the 20 gpm test, the backsplash was even more prominent, which was also true with the other smaller devices in this category. The Racor LG50 can be ordered through BoatU.S. and West Marine stores, internet and catalog sales.

Above: ATTWOOD FUEL VENT LINE SURGE PROTECTOR (Model #1675)

ATTWOOD FUEL VENT LINE SURGE PROTECTOR (Model #1675; retails for $23.99). This was the smallest of the inline devices we tested, about the size of a roll of quarters. This device is a gasoline-only model (no diesel model is available), but we were told by the manufacturer it is compatible with diesel as well. However, when we tested it with the soapy “gasoline” mixture at 10 gpm, this device did not allow the nozzle to click off in time and fuel bubbled from the deck fill and overflowed onto the deck. When we tested this device at 20 gpm, it “overpowered” the unit causing some minor spillage through the overboard vent, and a significant amount of backsplash from the deck fill. In fact, during our onboard boat test later, we witnessed a column of fuel about three inches in height and two inches in diameter shoot up from the deck fill when the tank became full. In both testing situations, the device made some gurgling noises to indicate a rise in fuel, so a prudent mariner should heed this audible cue and slow down. This product is available at BoatU.S. and West Marine stores, internet and catalog sales.

Above: ATTWOOD P-TRAP FUEL SURGE PROTECTOR (Model #1689)

ATTWOOD P-TRAP FUEL SURGE PROTECTOR (Model #1689; retails for $21.54). This unit looks different because it combines a fuel separator, fuel vent and flame arrestor in one unit and is roughly the size and shape of a fist. The Attwood P-Trap is installed on the inside of your hull with the vent portion replacing your existing overboard vent on the outside of your hull. Since this unit is plastic, we were concerned about the possibility of crushing it on a piling in a docking maneuver. To test, we again delivered fuel at 10 gpm and 20 gpm and the results were that as the unit suddenly prevented fuel from escaping overboard, backsplash from the deck fill occurred. With high speed fuel delivery, the pressure even slightly “overpowered” the unit, causing a simultaneous leakage of fuel overboard from the vent and fuel overflow on deck. The Attwood P-Trap Surge Protector is available through the BoatU.S. and West Marine catalog sales special orders department.

Above: Due to the sudden blockage of the vent by the rising ball in the inline separators, fuel (mixed with air), was then forced out of the actual filler hole!

Inline Fuel/Air Separator Summary: We discovered a very disturbing trend with most of the inline devices tested. For most of the units, pumping at 10 gpm until the automatic shut-off nozzle clicked off caused fuel to bubble over the mock-up’s deck. The results were even more disastrous when we pumped at 20 gpm. Due to the sudden blockage of the vent by the rising ball in the inline separators, fuel (mixed with air), was then forced out of the actual filler hole!

We did not slow down our pumping, even when we heard gurgling, which may account for some of the less than positive results. But since many people lock the pump handle and walk away, we felt that filling at full speed simulated a realistic situation. For these reasons we do not recommend using a hands-free device and we do recommend keeping your hands and face clear from the filler hole.

In general, the larger the unit and the slower you pumped, the better these devices performed. The fact is, there is simply is no substitute for careful and deliberate fueling. Listen to these devices, know how much fuel you need and slow down when you think you are near full. Do not top off and these devices may suit you just fine.