Safety Spotlight

Pre-mixed fuel

Don't forget to drain

By Rick Waite, Velcon Filters, Inc.

August 2000

There have been a couple incidents lately where large amounts of water have passed through IP qualified water absorbing cartridges. In both cases, it was found that the water bottoms in the upstream tanks were about a 50 percent water and 50 percent Di-EGME (anti-icing additive) mix.

Tests at the Velcon laboratory on the returned cartidges showed that water injected per the IP Monitor tests was trapped in the cartridges. It was also verified that a 100 percent water slug test will shut off the flow. However, a slug test with 50 percent water/50 percent Di-EGME results in increasing differential pressure, but an incomplete shutdown of flow, with a 10 percent or higher "leak rate" though the cartridge.

Considering the possibility of this situation with water bottoms heavily saturated with Di-EGME in pre-mixed fuel (Jet Fuel pre-mixed upstream with anti-icing additive) occurring in other systems, Velcon recommends the following precautions:
• Drain all sumps and tanks daily. Do not let water bottoms sit for long periods of time as they will increase in Di-EGME concentration.
• Install a delta P set switch (set between 15 and 25 psid) on existing Gammon gauges. When this triggers shut, replace the water absorbing cartridge(s) and check the downstream to see if any water has migrated.
• Use the more expensive water finding paste for pre-mixed fuels. Other brands do not change color in a 50-50 water/Di-EGME mix.
• Check with your probe manufacturer as to what concentration of water/Di-EGME mix would prevent the probe from reading correctly.
• Don't forget to drain.

Coalescers in pre-mixed fuel
In looking at the effects of Di-EGME on coalescers, we have found that various types of coalescers submitted for single element testing from both military and civilian customers still coalesced acceptably. Most of the interfacial tension (IFT) tests run on the first fuel over the first water from these coalescers were also in the acceptable range of 30 or more dynes/cm. These coalescers had been in service two or more years.

There were some coalescers which coalesced unacceptably (haze and/or predominately pinpoint waterdrop size). These coalescers had IFT readings of 12 dynes/cm or below.

Our feedback from the customers of the coalescers above was that the anti-icing additive was probably not being injected properly upstream. Either the fuel was too wet or the anti-icing additive had been contaminated by too much water before injection into the fuel. Dessicant dryers are needed to remove the water from the air entering the drum or container of Di-EGME. If a dessicant dryer is not used, moist air entering the Di-EGME container will transfer the water into the Di-EGME, and the Di-EGME won't go into the solution properly.

As with water absorbing cartridges, we recommend draining all storage tanks and F/S vessel sumps daily. Water bottoms will increase in Di-EGME concentration if it sits too long, and then downstream coalescers could be disarmed. Check the filter/separator sump drainings daily to see if any water removed is discolored, or if the fuel appearance above the fuel/water interface is cloudy. Discolored water and/or cloudy fuel coming from the filter/separator sump is a sign of disarmed coalescers. Drain daily.

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Excerpted from "The Clarifier," Velcon Filters' customer newsletter.