One thing is certain in this universe, there is no such thing as a perpetual motion machine. In the real world, which means outside of politics, you cannot get anything done without expending energy.

This rule applies in fuel systems: when fuel flows, it takes energy to push fuel through any valve, meter, filter or pipe. This results in a drop in pressure.

A clean filter element in a vessel will have many open passageways for the fuel to take, so it is easy for the fuel to get through. This is why new filters show a low pressure drop indication on your Gammon Gauge (or other differential measuring device), it takes very little energy to push the fuel through.

As a filter removes dirt or as a monitor removes dirt or water (monitors trap water as a gel), some passageways are plugged. This means that more energy has to be used to push the fuel through the remaining passageways. If half of the holes plugged, the fuel has to move through the remaining holes at twice the velocity. We measure that lost energy as pressure drop.

Filter separators add a complication. Dirt causes pressure drop in the same way as in any other filter element, but water acts different than in a monitor. A coalescer element only collects tiny water drops and makes them into larger ones, and if no water is present, the pressure drop is low. If significant amounts of water are present, the pressure drop increases, but if the fuel becomes dry again, the pressure drop can go back down. The difference is not very large, but can observed on the DP gauge.

On the other hand is the “clay treater” vessel, often called a “clay filter”. These are most commonly found in pipeline terminals and ship unloading facilities, but some are located on airports. In reality, they are not filters at all; the “activated clay” (like activated carbon) is designed to remove chemical surfactant contamination, not dirt or water. Increased pressure drop happens only if there are a LOT of big dirt particles or large amounts of water, which blocks off flow in the clay.

Pressure Drop = Differential Pressure = DP

So you don’t get an increase in the pressure drop (differential pressure or DP) between the inlet of a vessel and the outlet without something bad in the fuel, right?

Not true. Velocity is important. At zero flow, there is no pressure drop, even with virtually plugged filters. As the flow rate increases, DP increases, so an increase in the DP can take place simply because the flow rate is higher or decrease because flow rate is lower. For example, some aircraft can accept 850 gpm/3,200 lpm when the fuel tanks are empty, but this may decrease to just 150 gpm/560 lpm when you are flowing into the last small fuel tanks. The same is true in filling an above ground storage tank, the flow rate can vary as much as 50% or more from “head” pressure as the tank fills.

It is simple if you are at full system flow, you don’t need correction. But if you are flowing at a rate below 100%, you need to correct the indicated DP to what it would have been if the flow rate had been at 100%. Then you can keep a chart and see the trend. 100% is not the rated flow of any component, it is actual maximum flow you can achieve.

For manually correcting DP, there are charts, spreadsheet programs and electronics that can do this.

There are different views on monitoring DP and an increase in corrected DP means different things in different places. A gradual increase is expected anywhere. A sudden increase can signal a serious problem, depending on your experience at this facility. A sudden drop in corrected DP is always serious, it means that a filter element has come loose or failed.

Some people watch DP to spot sudden contamination changes. Some watch DP to schedule the next element change. Some watch DP to make sure the system is shut down and elements changed before DP becomes too high, damaging the filter elements and allowing debris downstream.

We have four alternatives:

1. Simply put a shutdown switch onto the Gammon Gauge (or other differential pressure control) and stop flow if DP gets too high.
2. Add a low pressure switch to determine if the DP is too low, indicating a loose element.
3. Add a differential monitoring control that automatically corrects the DP and keeps a record. Such controls have alarms and shutdowns for high corrected DP, notice trends and sense a decrease in corrected DP that could mean an element has come loose.
4. We can manually calculate corrected DP, with a spreadsheet or by using a chart. The weakness is that you have no automatic shutoff if DP suddenly goes up.

Clearly #4 is no longer allowed on into plane monitors by either JIG or ATA-103.

There are arguments, we’d prefer to avoid, as to what is best. We make a DP transmitter that gives the Gammon Gauge an output that can be connected to an electronic DP correction control and we make switches that can be added to a Gammon Gauge to indicate low or high DP. We also make a High DP shutdown control.

On refueler trucks and on other types of filter vessels, it gets more complicated. Refueler vessels with monitors usually have a higher flow rate through the monitor than the meter shows, because of the pressure bypass control, so correcting DP is very difficult. Some refueler trucks have filter separators, which are not as vulnerable to bursting. Some (rare) have filter separators AND monitor elements, either in a separate vessel or inside of the separator elements.

On fuel farm and terminal filters, it depends on experience. If you never see high DP and the flow rate really doesn’t vary, just keeping records and graphing DP may be enough. Any sudden increase, however, could mean much more than just some dirt, it may mean a mixture with other fuels, like diesel, where the mix is more of a problem than the dirt.

On clay, it means you have problems with water or gross dirt, and could also be more serious than you would think, due to mixed fuel. A low DP does NOT mean the clay is working.

REMEMBER: On any filter, a decrease in corrected DP can be as serious a problem and even a more serious problem than high corrected DP, it means you are very likely pumping unfiltered fuel!

This GamGram was originally published as No. 13 but its position has been exchanged with No. 25 because various revisions over the years have made it more of an interpretive discussion of the color rating technique. It would be a good idea to re-read the 1996 version of No. 13 before reading this article. First of all, let’s review the methods:

1. Color method – This is a field method using system pressure to force a measured volume of fuel through a test membrane. You then rate the color of the membrane, when dry, using the ASTM color booklet. “O” is beautiful; 10 is horrible. Use ASTM Method D2276 Appendix X1.
2. Matched weight method – Two factory-matched membranes are placed together, one on top of the other and a measured volume of fuel (in the field) then flows through both. The laboratory then weighs each membrane, subtracts the weight of the lower one from the top one and reports the amount of dirt that was collected on the top one. This method has the advantage of avoiding pre-weighing, coding and record-keeping before testing. Use ASTM Method D-2276.

Both of these methods have the advantage over a laboratory test of a sample collected in a can or bottle, in that the sample passes through the membranes directly from the flowing pipe that carries the fuel. The advantage we are referring to, of course, is that errors caused by unclean sample containers are totally eliminated. If it is not convenient to use the above methods, your last resort is to use ASTM Method D5452, which describes how to collect samples in shipping containers and perform gravimetric tests in the laboratory. This procedure, which was recently revised, recommends that the sample be taken from a flowing pipe and it recommends the matched-weight technique.

An argument against the color rating method is that the color of the fuel itself can stain the membrane, leading you to think the color is dirt. We have heard of jet fuel made from North Slope crude oil that will color a membrane to a B6 with no weight at all. It is rather obvious that a test is needed that will tell you whether it is dirt or color in the fuel. One easy way is to look at the back of the membrane and compare the color of the front to the reverse side. The difference in color is a measure of the filterable dirt in the fuel sample. It really astonishes us why this old, but simple technique has not been used except by a few people.

A refinement of this procedure is to put 2 membranes in the plastic monitor and then compare the topside colors of both. We like this much better, not only because you may disturb the collected dirt on the top when you turn it over on a color chart, but because color on top can show through to the underside of the membrane. Note: Do not use matched-weight refill membranes for this test because they cost four times more than standard membranes.

If we accept the fact that the above techniques are logical, the big problem now is how to decide how many numbers difference in rating between the top membrane and the lower one is acceptable. To our knowledge, no laboratory has published the results of any research on this, but we surely hope they get started.

One of our oil company customers has the following procedure for delivery of fuel to the aircraft:

He uses ASTM Method D-2276 as the test method, collecting 10 liters:

1. 1. If a single membrane shows a 3 or higher reading (rated wet), run a second test with a double membrane.
   2. If the difference is more than 2 numbers, do not use the fuel until a gravimetric test has been completed.
   3. If the top membrane is rated 6 or darker, the fuel must be tested gravimetrically before use, regardless of the color of the lower membrane.

We would modify this procedure by rating the membranes when dry and by specifying that a gravimetric test be performed if the color difference is as great as 2 numbers. In this way, you learn the weight significance of a 2 number color difference for that fuel. Once you know this, we feel the above plan can be used with confidence.

Do not forget that the color rating technique serves its greatest purpose as a way to detect a change. That is why tests must be performed on a regular schedule with absolutely no variation in procedure. We do not propose to go through a step-by-step procedure because you can easily get this from other sources such as our MiniMonitor instruction booklet. However, there are a few special points that bother us:

1. The Sampling Point — Read GamGram No. 6 and Bulletin No. 3. Why do some people expect to obtain accurate results from a sampling connection that generates rust and debris? Don’t laugh! This is one of the worst problems. We often find rusty gate valves with graphite stem packings in a sampling connection where all other components are stainless steel.
2. Technique
• Do not over-tighten the monitor holder. There is no need to apply great force. O-rings do the sealing. If you have leaks, order new o-rings. Over-tightening can cause membrane breakage around the clamped edge.
• Never move a valve or start and stop a pump while a test is in progress. If you must do these things, you must first stop flow through the membrane with the Flush/Test valve. Then after system flow has been re-established, continue the test by opening the Flush/Test valve.
• Never turn a flushing valve rapidly. How many times have you found a broken membrane? We believe that this is caused by rapidly starting the flush cycle in a high pressure system. The fuel bypasses the membrane, but it can enter the plastic monitor from the outlet side, compressing the trapped air in the monitor. A membrane has little strength and fails from this slight reverse flow. Turn the flushing valve very slowly.
• Another cause of broken membranes is the double-acting syringe that a competitor supplies with his test kit. Sometimes the internal check valves stick, allowing fuel to be forced backward through the membrane when you push the handle inward. To avoid this, remove the plastic monitor before you push in the handle.

We continue to hear arguments about diaphragm operated slug valves. Should they be installed so that flow goes upward through the seat or downward? Should they be located upstream or downstream of a diaphragm failure? Can a slug valve be a check valve?

Filter separators are most always furnished with three components to provide for automatic water drain and automatic shut-down in the event of a water slug condition. (Refer to GamGram 10, GamGram 11 and GamGram 12.) The three components are as follows:

• Float control
• “Slug” or discharge valve
• Automatic water drain valve

If there is no water in the filter separator sump, the ball of the float control stays down. If water collects to lift the float to a mid-position, the water drain valve will open automatically until the water level has dropped. If the water does not drain rapidly enough, as in the case of a “slug” of incoming water, the float rises to a top position and causes the slug valve to close until the water level goes down.

Recognizing that there is controversy on the questions in the first paragraph, we are “throwing down the gauntlet” with a few statements of fact:

If the slug valve diaphragm fails:

1. When the float ball is down or at mid-position and flow is downward through seat, slug valve allows continued flow to some degree.
2. When the float ball is at top position and flow is downward through seat, slug valve closes tight with no down stream leakage.
3. When the float ball is down and flow is upward through seat, slug valve allows substantial flow.
4. When the float ball is up and flow is upward through seat, slug valve allows continued flow to some degree.

The amount of flow that will occur in 1, 3 or 4 depends on the size of a diaphragm rupture. A very small break can result in a rather large valve opening.

Obviously, the most dangerous situation is 4. It takes no great mental effort to conclude that we want zero flow in a water slug situation. Therefore, the arrangement shown in GamGram No. 12 is desirable.

Do you know how to figure out whether your slug valve is flowing upward or downward through the seat? Look at the 3-leg line that is cast in the valve body. It represents the bridgewall as shown below:

The 4 statements above are true regardless of whether the slug valve is located upstream or downstream of the filter separator. They also apply for all brands of diaphragm valve usually found in aviation fuel systems: ClaVal, Baker, Oil Capital, AO Smith and Harwood.

No brand of standard slug valve will function as a check valve whether upstream or downstream of a filter separator, whether operating in one direction or the other, unless the pilot circuit is especially designed to add this feature. Kits are available that will make any slug valve work as an excellent check valve.

Many installations are being made today with a conductivity probe replacing the float control in the filter separator water sump. The slug valve is then controlled by using a solenoid valve in the pilot circuit. All of the four statements regarding diaphragm rupture also remain true for this type of installation.

Other Diaphragm Failures

Some brands open when pilot pressure is directed to the top of the diaphragm. Others open when pilot pressure is vented. See GamGram 10 to learn which type you have.

• Automatic drain valves:
  1. If pilot pressure is supposed to open the valve, pilot line flow will be vented instead of causing opening.
  2. If the valve is supposed to open when pilot pressure is vented, it will stay closed but water will vent through the pilot lines.
• 3-way pilot on slug valves:
  3. If pilot pressure is supposed to cause the slug valve to open, it will stay closed. Leakage through the diaphragm will go downstream.
  4. If the slug valve is supposed to open when pilot pressure is vented, it will stay closed. Leakage through the diaphragm will be vented.

As a result of this GamGram, many of our readers will decide to reverse the direction of flow in their slug valves. Before starting such a project, be sure you understand exactly how all of the pilot lines must be re-routed. Contact the manufacturer or one of our representatives for assistance.

If you are reading this GamGram, you are somehow involved in aviation fuel or fueling operations. If you see any intelligence in the above quotations, you have been brain-washed just the same as the guy who changes his brand of beer because the TV commercial says their brand tastes better if you drink more than “one or two.”

There are obviously no unimportant flights. Human beings in little planes are just as alive as those in big planes. When you die from the crash of a Boeing 747, you are just as dead as if a one-man helicopter crashed into your house and killed you. Granted that there are more people in large planes, but there is simply no logic in an argument that the required extent of safety precautions is proportional to how big the airplane is built.

Would it be sensible to say that the smaller the plane, the more water and dirt can be in the fuel? If your brain is properly in gear, you surely will agree that flying can be bad for your health in any aircraft if the fuel is dirty, wet or otherwise contaminated.

The number of new low capacity refueling installations being made in the USA today is far greater than at any previous time. Most of these are for jet fuel but avgas installations are also being built at a high rate. There are several reasons for this increased activity in the face of escalating fuel prices and fluctuation availability.

Traditionally, major oil company engineers have scrutinized plans for new installations if they did not design the entire system themselves. This control is all but lost today in the USA, and we would argue that a high percentage of new projects are virtually out of control.

The FAA has never had any list of minimum standards for fuel handling systems or procedures, because the oil companies have done a remarkably good job over the years. This control is still evident in airlines operations where there are fuel supply contracts. Also, the airlines have operating manuals that the FAA demands be followed. The problem area is new installations where an oil company is often not involved today.

Fuel that is bought on the spot market has no major oil company behind it; it may be excellent, or it may be terrible. Some of this fuel is coming from places the major oil companies like to call “backyard tea kettles”. After all, it really is not difficult to make kerosene; all you need is a supply of crude and a distillation column. Making jet fuel that conforms to all requirements of ASTM D1655 requires more elaborate equipment but in these days of unreliable availability, many operators seem willing to burn anything that “looks” like jet fuel.

So here we are, back to the basic problem – people who have no background or experience in fuel handling are deciding how facilities will be designed and operated. And just because an engineering company is commissioned to design the facility does not solve the problem. We have dealt with some that did not know a coalescer from a slug valve or the difference between avgas and jet fuel. It is encouraging that a few qualified aviation fueling specialists who have retired from major oil companies and airlines are now operating as independent consultants.

There are significant differences in minimum standards among oil companies. If you ask companies A or B, they will say that epoxy lining of the underground tank is not necessary while C, D and E insist on it. Of course, A and B may feel that they have other controls or procedures that make epoxy lining unnecessary. If the FAA tried to set up a standard that specified epoxy lining, A and B would object. Oil company E would object to a requirement for a floating suction. C insists that the swing joint of a floating suction be at the centerline of an underground tank while all the others demand that it be at the bottom. There are few points of complete agreement and no fuel suppliers want the requirements of another company imposed on them. THE BOTTOM LINE IS SURELY THAT THE FUEL MUST BE CLEAN AND DRY IN THE AIRCRAFT.

If there is one principle to which everyone agrees, it is that repetitive and redundant controls are responsible for the generally high degree of safety we have today. In other words, it is not ONE thing you do to have clean fuel; you do MANY things. If one or more fails, the others fill the gap.

The following list of 7 design features provides optimum control and there will be little argument on the desirability of each one.

Our proposition is that a facility does not need all of these features. It must have No. 5, it must have either No. 6 or 7, and at least 2 of the first 4 features. We would consider this a bare minimum facility to insure that contaminated fuel does not reach the aircraft.

Why do we say that either No. 6 or 7 is absolutely necessary? Because, after the filter separator sump has filled with water, there is no other way to keep it from going into an aircraft. Take a look at your facility. If you have no positive shut down feature, you are not protected.

People who work with jet fuel handling equipment need special knowledge that the experienced old-timers often forget to pass on to new personnel. In our GamGrams, we tend to talk about the bigger issues and problems but there are many little “tricks of the trade” that we thought you might like to see in one issue.

Buna N – Viton – Neoprene

How many times have you wanted know what compound was used to make an O-ring? They are all black and they look the same. The only test we know of is destructive – you must burn it. Therefore, if you know you need one Buna N O-ring and you have 2 of them, cut one and hold a match to one end – be sure it is clean and dry first:

All too frequently, we are requested to supply Neoprene gaskets for jet fuel. We thought that the entire industry learned this lesson many years ago. Buna N is the proper choice for jet fuel because it swells much less than Neoprene. However, if very low swelling is necessary, such as in dynamic or moving seals, most manufacturers can offer special, low swelling grades of Buna N. If near zero swell is needed, Viton A is the choice.

Possibly the most useful gadget in a tool box is a simple magnet. Everyone knows that carbon steels are magnetic – a magnet attracts it. People also know that a magnet is not attracted to aluminum or brass but few of them know that a magnet is not attracted to stainless steel.

Unfortunately, there is an exception to this rule. When we say “stainless steel”, we generally mean a grade of material that will not rust. These are known as 300 series stainless steels — they contain both nickel and chromium — they are non-magnetic. A grade known as 400 series stainless steel is also sold that has no nickel and it is magnetic, but it is not as corrosion resistant as 300 series. It will rust, but it will not pit deeply the way carbon steel does in mildly corrosive conditions.

One of the most common errors we see in jet fuel facilities is the use of galvanized pipe fittings. The oil industry has been fighting this battle for 25 years but dealers and fuel handlers continue to make the same mistake. We saw 2 cases just last week.

Copper, zinc and cadmium are bad for jet fuel because of their effect on the thermal stability of the fuel – deposit build-up in the hot section of turbine engines. A further problem of zinc and cadmium plating is that it often separates from the base metal, creating dirtier fuel.

Some engineers write specifications that exclude all copper. Clearly, this is an over-reaction to the rule. Brass hose fittings, copper tubing and brass fittings for gauge lines, brass bushings in fueling nozzles, bronze pump bushings are reasonable locations because the contact area is very small. Bronze bodies for control valves, copper piping and bronze pump housings are obviously large surface area items and should not be used.

Most people know that a compound must be used to seal tapered pipe threads. One of the first problems in jet fuel systems was with compounds that got into the fuel and plugged screens and nozzle jets. PTFE tape rapidly became the answer to the problem but it created 2 new problems.

1. Tape strings – if all of the threads on a fitting are wrapped with tape, the portion of the tape on the first thread will be sliced off as the fitting is screwed in — now you have a string that can cause many problems

• Answer: never put tape on the first thread.

2. Broken fittings – the low friction of PTFE allows the mechanic to take extra turns as a substitute for cutting and re-threading a pipe that is too long. In other words, the tape makes it very easy to turn a fitting. If care is not exercised, the fitting will split. If the fitting is a valve worth $400.00, this is an expensive proposition.

• Answer: Experience is the only answer. However, we have fewer problems when we use a combination of PTFE tape and a lubricant, such as petroleum jelly (Vaseline). The lubricant further reduces friction so that the mechanic has a more consistent “feel” for how tight he is making the joint.

The next GamGram will discuss fuel system designs and trade-offs, but we expect to publish a future issue that will cover more “Tricks of the Trade.” If you would like to suggest any of your own tricks, we will be happy to acknowledge your contribution.