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Old 08-06-2015, 01:41 PM   #1
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Trim tab problems

After owning Compromise for three years, trim tabs finally made it to the top of the list. Bennett tabs, reservoir was empty. Filled it, push the down buttons and can hear the pump run but the tabs don't move. No leaks inside the boat. What are common failures? Stuck cylinder, leaking cylinder, bad pump? Major effort to look at the reservoir but I guess that will be my next step to see if the fluid level has gone down.


Thanks,


Bob
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Old 08-06-2015, 01:55 PM   #2
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Old 08-07-2015, 06:38 AM   #3
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No leaks in boat, empty reservoir might mean actuator leak. worry about that later.

Hear the pump run but tabs don't move may mean the solenoid valves are not opening, low probability both failed so probably an electrical issue which is where most problems end up.

The connector from the harness to pump is always a place to look for a weak connection. The solenoid wires are red and green. Tabs up are the yellow wire, down is the blue wire.

What kind of switch do you have? If its a Bennett rocker all the screws in the back of the switch have to be there, no empty screw holes. The screws make contact and jump multiple circuits.

Orange to switch: Power Black from pump: ground

Because you hear the pump I assume power is getting to it.

Blue: Motor forward for tabs down
Yellow: Motor reverse for tabs up

At the same time the motor is turning the appropriate valve must open

Red: Starboard
Green: Port

So blue and green energized will make the port tab go down.

If when you get the electrical end sorted out you will put the tabs down overnight and note the tab locations the next day. If they have crept back up it indicates a leak somewhere. If the leak is at an actuator a simple O ring replacement will get you going.

Bennett has the best customer service tech's in the Industry, and Tom is the best of the best.

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Old 08-07-2015, 10:01 AM   #4
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Bit the bullet and pulled up the bed. Fluid level goes down and back up for both actuators so they must be moving. My crude measuring stick appeared to show about 2" of movement. Will have to do this again when the admiral is on board and I can watch the tabs move while she pushes the buttons. They are under the swim platform so really hard to feel or see. Will do the next test at night with an underwater flashlight.


Now that I think about it, I forgot to put the unit back in its holder. So I can see another bed disassembly coming up.


Thanks for all the help, will report back later,


Bob
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Old 08-07-2015, 11:03 AM   #5
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Standard Actuator travel is 2.5". If you have 12" chord tabs the actuator attaches at 9" on the tab, so the trailing edge will travel more than 2.5"

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Old 08-07-2015, 02:56 PM   #6
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Since they are below the swim platform my measurement was kind of half as?. Had to leave, but next time I will get a more accurate measurement.
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Old 08-07-2015, 04:52 PM   #7
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It would be very unusual for you to have oil in the reservoir and for the tabs to move but not go full travel. If the work they work, if they don't there's a reason.

If you can get them both all the way down and then measure or visualize them and then check the next day that will tell you if you have a leak. If they creep back up overnight there is a leak, either internally back into the reservoir, somewhere in the plumbing into the bilge, or the seals on the actuator.

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Old 08-07-2015, 05:17 PM   #8
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Agreed, a test for next time. There is obviously a leak since the reservoir was empty, but how much of a leak? Since the fluid returns to the full level with the tabs up it is obviously not a catastrophic leak to where I'm pumping fluid into the water.


Since I don't know how much or how little POs have used the trim tabs, the fluid might have leaked out over a period of years.


Will do a over night leak down test next time I'm on the boat.
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