Bennet trim tab goes down, not up, regardless of up/down button

[Seawilly1421]

I have an old set of dual actuator(per tab) Bennet trim tabs. This year the port side tab goes down normally but will continue to go down when the up button is pressed. The port side tab is working fine. Pump has power, reservoir is full, sounds and looks normal, no leaks on the actuators or through our the system. What might cause the actuator to go down regardless of the down or up button depressed?

 

[alldodge]

Most likely its the switch
There is several vids at the Bennett site showing how to test

Here is just a pdf
https://bennetttrimtabs.com/wp-content/uploads/2015/02/trimtab_troubleshooting.pdf

 

[Seawilly1421]

Ok, the up switch(button) is sending the tab down, you are suggesting the switch maybe bad? The tab functions normally when the down button is pressed.

 

[alldodge]

I'm just guessing, but not knowing exactly what type of controls you have. Mine used 2 large rocker switches which were DPDT type. It could be that inside the switch is where the problem is.

At any rate need to troubleshoot to find out

 

[alldodge]

this

 

[Seawilly1421]

I'm just guessing, but not knowing exactly what type of controls you have. Mine used 2 large rocker switches which were DPDT type. It could be that inside the switch is where the problem is.

At any rate need to troubleshoot to find out

Thanks, tying to do so. The control is a 4-button switch, old style, maybe early '80's as much as I can tell.

 

[dingbat]

Replace the old switches with the new rocker switch

 

[Seawilly1421]

Thank you I was thinking the same. It that does not fix the problem why would the up and down switch just send the tab down. How, where, does the hydraulic fluid go? I’m wondering the fluid is on the wrong side of the plunger in the actuator. Would that mean I’m further ahead with an actuator?

 

[dingbat]

Thank you I was thinking the same. It that does not fix the problem why would the up and down switch just send the tab down. How, where, does the hydraulic fluid go? I’m wondering the fluid is on the wrong side of the plunger in the actuator. Would that mean I’m further ahead with an actuator?

The actuators are spring loaded up.

Up and down switch performs two functions.
1. They turn on the pump
2. They position the spool valve between the pressure (down) and suction (up) side of the pump.

Your pump is working but something is wrong with the spool control part of the circuit.

Can’t give detailed instruction. Have not messed with mine in years. Suggest you grab a schematic and troubleshoot the valve circuit. Should be pretty easy to check the switch with continuity testing

 

[Chris1956]

Bennett trim tabs are usually spring loaded. That is, when moving down they are under hydraulic pressure. When moving up, the fluid is withdrawn from the actuator and spring pressure causes them to come up. So unless the seals leak, there will not be fluid on both sides of the piston.