Separator Vessel Sump Float  & Pilot Testing


Coalescer Separator Vessel Sump Piolt & Float Testing
NOTE: The following is a culmination of three Gammon GamGram's discussing coalescer / separator vessel sump float and pilot testing.

THE GAMGRAM
Gammon Technical Products, Inc
2300 Hwy 34 Manasquan, NJ 08736 USA
Ph 7328-223-4600 - Fax 732-223-5778

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.

"AUTOMATIC CONFUSION"

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.

Gammon Table 1: Pilot Positions

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.

Table 2

Port

Identification

ClaVal

Watts

Before 5/86

Watts

After 5/86

Brooks

Oil Capital

Smith

Supply

S

A

P

D

P

D-9

Water Drain Valve

W

C2

DV

A

W

A-2

Discharge Valve

F

C1

SV

C

A

B-5

Vent

D

B

E

B

E

C-6

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.

Table 3
Float Position ClaVal Watts

Before 5/86

Watts

After 5/86

Brooks Oil Capital Smith ClaVal

CFF12-H3

Up F-S, W-D C1-B, C2-A SV-E, DV-P C-D, A-B A-E, W-S 5-6, 2-9 F-D, W-S
Intermediate F-D, W-D C1-A, C2-A SV-P, DV-P C-B, A-B A-S, W-S 5-9, 2-9 F-S, W-S
Down F-D, W-S C1-A, C2-B SV-P, DV-E C-B, A-D A-S, W-E 5-9, 2-6 F-S, W-D

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 operated pilot.

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 humorous experiences I have had, in traveling from airport to airport these many years, was with a customer who was vigorously resisting spending money to change long overdue elements in his filter separator, "because we never have water in our fuel". We were standing beside the filter and right after he finished talking, a stream of foul dark water started to gather around his shoes. The automatic water drain valve had opened.

And then there are the operators who put plugs in the outlet ports of their automatic water drain valves. Many of you have manual valves that are kept closed upstream or downstream of the automatic water valve. If you do this to stop leaks, you must realize that you have completely eliminated this factor of safety. In fact, if the vent tube is connected to a plugged drain valve, you will prevent the slug valve from operating correctly. Why not repair the leak? Every manufacturer can supply spare parts with diagrams showing how to replace seals. Or if you do not want to do your own repairs, there are many qualified shops (including ours) that do this work.

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.

Do you have float testers on your float operated pilot valves? This handy little gadget is just an 0-ring sealed screw or plunger that you can open to cause the float to go up and down while the system is operating With this device, you can quickly check the automatic drain valve as well as the discharge valve. Almost all models of float operated valves can be equipped with testers. Each manufacturer sells a kit with the necessary parts but on some models you must drill and thread a hole in the valve body.


When did you last test your floats to see if they will float on a fuel/water interface? Many people now perform this test on a regular schedule. There are two procedures in use:

Method 1: A hand pump is used to force water in the manual drain valve. The water is drawn from an open bucket so that you can see exactly how much water is being used. This method will also allow you to test the automatic drain valve and the discharge valve.

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.

Method 2: Remove the float and drop it in a bucket that has 4 inches (1 0 cm) of fuel on top of 4 inches of water. If the float sinks in the water, you must return it to the manufacturer to be repaired or replaced.

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.

Table 2: Coalescer Separator Pilot Valve
In Fig. 1, (above) there are two pilot valves shown, X and Z. X is an On-Off pilot valve and the other (Z) controls the rate of flow. Watts*, Smith, and Oil Capital make On-Off pilot valves that are similar. Each requires a pressure signal to cause the slug valve to open. A pilot of this type is shown in Fig. 2, (left) in the closed position. Note that pressure from the supply port M is directed to Y, the cover of the slug valve, to close it. In other words, pressure from M goes through port R, then port J and to port Y on the cover. If control pressure from the float operated pilot valve is applied at port L to open the on-off pilot, the slug valve cover is vented through ports Y, J and N of the on-off pilot into port P. The slug valve then opens because system inlet pressure at M is greater than outlet pressure at P.

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
*Formerly known as Baker and more recently Muesco.

Gammon Pilot CutawayAll manufacturers make rate of flow pilots (Fig. 3) that are almost identical. To control it, an orifice plate is located at the inlet of the discharge valve. Pressure taps (G1 and G2) are located at the downstream and upstream sides of the plate which has a hole in it that is somewhat smaller than the piping. G1 is the pressure upstream of the orifice plate while G2 is the pressure after the orifice plate. When flow passes through the orifice, the pressure loss across the plate becomes greater and greater as the flow rate increases. In other words, an orifice plate is a simple flow meter. By taking these two pressures as G1 (high) and G2 (low) to a pilot valve Z, the diaphragm will move away from the side having the highest pressure. This force is resisted by a spring, but the tension on the spring can be changed by turning the screw at the top. This pilot valve will adjust itself to try to maintain a perfect balance but in so doing, it regulates the amount of "pilot" flow that can pass through port K. This will influence the pressure that is in the slug valve cover to modulate flow rate. For example, if the flow through the orifice plate is too high, its pressure drop is also high. This results in a partial closing of port K, restricting pilot flow. This causes more pressure on top of the slug valve diaphragm, causing it to close slightly to correct the excessive flow rate.


Gammon Pilot Figure 4The ClaVal system is exactly the same, except that the On-Off pilot (Fig. 4) works in the reverse of the one in Figure 2. In the position shown, control pressure is being applied at L. Supply Pressure at R goes thru J and directly to the slug valve cover through port Y to block fuel flow through the main (slug) valve. To open the slug valve, L must be vented so that pressure at R will lift the diaphragm and close port H. The orifice then supplies "pilot" flow and all other functions are the same as described for other brands. The slug valve cover is vented through port J to N and then to P.

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.

We have reproduced Tables 2 and 3 from GamGram 10 so that you can follow a typical troubleshooting problem. We cannot review all failure modes for all brands, but this one shows the reasoning technique. You have ClaVal equipment and the slug valve will not open. Disconnect the fitting at L in Figure 4. If flow comes out of the tube, the float is up so water is in the sump and that is the reason the slug valve will not open. If the automatic water drain valve will not open, its diaphragm may be found to be leaking and water flow will be found in the vent tubing from the float valve. If the On-Off pilot diaphragm had failed, a fuel flow would have been found in the vent before the fitting at L was disconnected.

Table 2

Port

Identification

ClaVal

Watts

Before 5/86

Watts

After 5/86

Brooks

Oil Capital

Smith

Supply

S

A

P

D

P

D-9

Water Drain Valve

W

C2

DV

A

W

A-2

Discharge Valve

F

C1

SV

C

A

B-5

Vent

D

B

E

B

E

C-6


Table 3
Float Position ClaVal Watts

Before 5/86

Watts

After 5/86

Brooks Oil Capital Smith ClaVal

CFF12-H3

Up F-S, W-D C1-B, C2-A SV-E, DV-P C-D, A-B A-E, W-S 5-6, 2-9 F-D, W-S
Intermediate F-D, W-D C1-A, C2-A SV-P, DV-P C-B, A-B A-S, W-S 5-9, 2-9 F-S, W-S
Down F-D, W-S C1-A, C2-B SV-P, DV-E C-B, A-D A-S, W-E 5-9, 2-6 F-S, W-D

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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