Vessel Sump Piolt & Float Testing
This brief will explain the operation and testing of control valves for filter separators. These combined issues deal primarily with the differences among various brands on the market.
There are probably no more than 5 GamGram readers in the entire world who already know how to troubleshoot each of the various brands of separator controls. How many times have you stood beside a filter and wondered how to find which pilot valve is not operating correctly? With at least 5 different brands of valves on the market, you need to carry a library with you!! This writer has stumbled his way through many a troubleshooting expedition and was embarrassed one too many times by lack of needed information. To solve this problem, data on all known valves were collected and tabulated. The exceptional cooperation of each manufacturer is acknowledged. We have not included in this study the single circuit controls that are used on mobile equipment.
The diagram in Figure I shows the control system. The primary control is the float operated pilot valve. The float is weighted so that is floats on water but not on fuel; it rides on the interface between water and fuel. Table I shows that the drain valve opens as water collects but if water gathers faster than it can drain out, the discharge valve closes until the water level is again safe.
Each manufacturer uses 4 different ports on their float operated pilot valves. These ports are marked differently by each manufacturer and one (Smith) has no marks at all. In Table 2 we have used identifying letters and numerals that refer to clock positions, e.g. the water drain connection port is at the 2 o'clock position.
NOTE: In the 1996 revision, this figure has been revised for clarification.
To troubleshoot a system you must know which ports should be vented and which should be pressurized under various conditions. Table 3 shows this for each brand. F-S, W-D means for Cla Val that port F is internally connected to port S while port W is internally connected to port D. In other words, if you blow air in port F, it will come out of port S. Air into port D comes out of port W.
All of the standard side and bottom mounted float pilot valves operate according to the table with one exception. The Cla Val 1626AF bottom mounted combination float pilot and automatic drain has no visible supply, water drain valve or vent ports so it must be bench checked with air to troubleshoot.
Suppose you have a Smith system and are experiencing a consistent fuel leak through the water drain line when you know the float is down. Disconnect the vent tube to see if it is the source. If so, you know the float valve has a bad seal, allowing fuel to leak into the vent port. If the vent does not leak, you can conclude that the water drain valve seal has failed or is held open by dirt particles.
If the same problem occurred with a Cla Val system, a leak at the vent could be in the float pilot but because F and D are connected, you must disconnect tube F to see if the fuel is coming from the ON-OFF control pilot on the discharge valve. If not, you can conclude that the drain valve seal has failed or is dirty.
Table 3 is especially useful when you are
trying to analyze faulty operation. For example, the discharge valve fails to open in a
Smith system. Table 3 shows that 5 and 9 are connected so if you loosen a fitting on the
tube that runs from the float operated pilot valve to the discharge valve you should have
fuel pressure coming from the float operated pilot valve. If you find that the line is
pressurized, you can conclude that the trouble is at the discharge valve, not at the float
We want to make a final point about automatic drain valves. In our opinion, they are not totally reliable. We mean that there can be a massive spill if one sticks in the open position because a foreign object becomes caught in the valve seat. We recommend that they not be used. To deactivate an automatic drain valve, plug the water drain port on the float pilot of all brands. However, in the case of Cla Val, the automatic water drain valve must also be removed completely.
NOTE: The following is the second in the three part series...
Did you know that to this very
day there are oil companies and airlines who never test the control valves on filter
separators? if you never test the float pilot valve, how can you know that it will operate
if a big slug of water comes along? Are you saying that you never have water anyhow? At
this point I make a rude remark and remind you that you have that equipment to save your
skin in the event that something unexpected happens.
One of the great controversies in the
aviation fuel world is whether or not to have an automatic drain valve. Some people have
decided to have a float operated pilot valve and a discharge valve only. In other words,
they want flow to stop if water collects. The operator then must manually drain out the
water before fuel flow can begin again. If you ever wish to deactivate an automatic water
drain valve and retain normal operation of the discharge (slug) valve, we offer these
words of caution. The vent ports of all brands of float operated pilot valves must be left
open. You must plug ClaVal port W, Brooks Brodie port A, Baker port C2, Oil Capital port W
and Smith port 2. You must completely remove the ClaVal and Brooks Brodie automatic drain
valves but you need not do this in the case of other brands.
NOTE: A mechanic recently decided to run
this test by using city water pressure. When I pointed out that the refueler pressure
could be greater than the city pressure, he agreed that people might be unhappy at finding
jet fuel in their kitchen sinks.
Leakage is by far the most prevalent complaint regarding filter separator controls. Many of these complaints are not fully justified because some people do not understand that a "spit" of fuel is discharged from the vent every time the system is operated. This is caused by the operation of the diaphragm in the On-Off pilot valve and amounts to only a few drops. Continuous dripping is most frequently caused by dirt particles under the seat of the automatic water drain valve. This is why many operators require that a Y strainer be located upstream of the drain valve. A very useful device that is often installed in the discharge line from an automatic water drain valve is a flow indicator. Many different models are on the market (pin wheels, flappers, jiggling balls, etc.). In a drain system that is piped to a waste tank, one of these flow indicators provides a visual indication of discharge flow.
NOTE: The following is the third in the three part series...
How many people think that a water slug
valve will close because it "senses" a slug of water? It is amazing how many
people believe this but those of you who read GamGrams 10 and 11, know that the
"intelligence" comes from a device called a "FLOAT OPERATED PILOT
VALVE" or an electrical device that can sense the difference between water and fuel
in the sump of a filter separator.
A very curious thing about slug valves is
that people outside of the filter separator business refer to the very same valve as a
diaphragm operated control valve. The term "slug" was dreamed up many years ago
by filter separator people because it was necessary to stop flow in a fuel system if a
"slug" of water collected in the sump at a rate greater than it could be drained
away. A hydraulic signal to the slug valve (also known as the discharge valve) will cause
it to close to prevent fuel flow until the water level has been reduced to a safe range.
Sometimes the slug valve is called a RATE
OF FLOW CONTROL VALVE. All this means is that it is a slug valve that was modified to
perform both functions. It can operate as a slug valve and it can also automatically limit
the flow rate to the maximum rating of the filter separator. This is an important optional
function because filter separators are very velocity limited. Note: If you want to upgrade
your slug valve to control flow rate, we can tell you how to do it, on request.
The tricky feature in the On-Off pilot is the orifice shown by an arrow. If the on-off pilot has been opened to start main valve flow, the orifice allows a small "pilot flow" from R to bypass the main valve through port N and then to P. When a rate of flow pilot is added, you can see that by regulating or throttling this "pilot flow"' the pressure at the slug valve cover can be regulated to cause the main valve to modulate between the open and closed positions.
NOTE: In the 1996 revision, these figures
have been revised for clarification
When slug valve problems occur, our
experience has been that diaphragm failures are the primary cause. These are easy to find.
Disconnect the fitting at Y and turn on the pump. Continuous flow from the slug valve
cover means a diaphragm failure. A failure of the On-Off pilot diaphragm in Figure 2 can
be detected by disconnecting the fittings at N and L. Apply pressure at N and look for
leakage at L. A failure in the rate of flow pilot diaphragm is found by disconnecting one
of the orifice pressure fittings, G1 or G2. Leakage indicates failure of the diaphragm.
In conclusion, we feel that we should have emphasized in GamGrams 10 and 11 that the Supply fuel should be filtered to prevent malfunctions in the float pilot. Supply must come from downstream of the coalescers or be separately filtered. Also, in retrospect, we might have recommended a 40 mesh strainer upstream of the automatic drain valve. Most leaks from that valve are caused by dirt in its seat.
Related: Gammon Coalescer Separator Portable Sump Float Tester (.pdf 708kb)
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