Bennett V351HPU1 12V Hydraulic Power Unit for Trim Tabs

The Bennett V351HPU1 (part V351HPU1) is the 12-volt electrohydraulic power unit (HPU) that powers the entire Bennett hydraulic trim tab system. The HPU contains the 12V hydraulic pump that generates the operating pressure, the two electrically-actuated solenoid valves that direct hydraulic fluid to the up or down side of each trim tab actuator, the fluid reservoir that holds the operating fluid (standard automatic transmission fluid), the Lexan protective cover, and the integrated wiring connections for both the helm switch input and the actuator outputs. The right HPU for any boat running Bennett hydraulic trim tabs, whether you're replacing a worn-out original or installing a fresh Bennett tab kit from scratch.

What the HPU actually does. Hydraulic trim tab systems work by using fluid pressure to drive the trim tab actuators (the rams that mechanically push the tab plane up or down). The actuators are double-acting hydraulic cylinders. Pressure on one side of the piston extends the actuator (which deploys the tab down). Pressure on the other side retracts the actuator (which pulls the tab back up). The HPU generates that pressure on demand: when the helm switch tells the HPU to lower the tabs, the pump runs and the appropriate solenoid valve opens to send pressurized fluid to the down side of the actuators. When the switch tells the HPU to raise the tabs, the same pump runs and the other solenoid valve opens to send fluid to the up side of the actuators. When the switch is released, both solenoid valves close, the pump stops, and the trapped fluid in the actuators holds the tabs at their current position with no continuous power draw.

Two solenoid valves for tab control. The dual solenoid valve design is what gives Bennett hydraulic trim tabs their characteristic precise positioning and rock-solid hold. Each valve closes hydraulically tight when de-energized, which means the trapped fluid in the actuator can't bleed back through the valves. The tabs hold exactly where you set them, against any normal hydrodynamic load, without the system having to constantly run the pump to maintain position. Most other electric trim tab designs (and electric actuator-style tabs) hold the tab via mechanical means (ballscrew, worm gear). The hydraulic-lock approach is what makes Bennett tabs so well-known for staying exactly where you put them at any speed.

Strength to hold even the largest tabs. Bennett offers trim tab planes from 9 x 9 inches up to 24 x 18 inches and beyond. The V351HPU1 has the pressure capacity and the fluid flow rate to drive any tab in the Bennett line, including the largest tabs on heavy offshore boats. For typical recreational use (12 x 9, 12 x 12, 12 x 18 tab planes on 18-30 foot boats), the HPU is well within its working range and lasts for many years of service. For the largest tabs on heavy boats, the HPU still has the headroom to drive them without strain.

Lexan cover protects against wash-down. The Lexan polycarbonate cover snaps over the top of the HPU's electrical and hydraulic components, protecting them from occasional water exposure (engine compartment wash-down, rain water leaking past hatches, splash from rough-water operation). Lexan is the high-impact-resistant clear plastic Bennett uses because it doesn't crack from impacts or heat-stress like cheaper acrylic covers do. The cover comes off easily for service access (filling fluid, replacing solenoid coils, troubleshooting wiring) and snaps back on after.

Translucent reservoir for at-a-glance fluid check. The plastic fluid reservoir is translucent so you can see the fluid level without removing any covers or unscrewing any fill plugs. Visual inspection during routine engine compartment checks tells you immediately whether the system is at the proper fill level. Low fluid is the most common cause of trim tab issues (slow operation, weak hold, air in the lines), and the at-a-glance check makes catching low fluid a 5-second visual.

Uses standard automatic transmission fluid. The Bennett HPU uses automatic transmission fluid (ATF) as the hydraulic working fluid. Any Dexron III or equivalent ATF works. ATF is the right fluid choice because it has the right viscosity range across temperature swings (from cold winter starts to hot summer engine compartment temperatures), it has the right anti-foam additives to prevent air entrainment in the system, and it's available at every auto parts store at a low price. Don't use brake fluid, hydraulic jack oil, or motor oil. Use ATF.

Mounting and dimensions. The V351HPU1 measures 4 x 7.5 x 5.5 inches and weighs 5.57 lb. Mounts horizontally to a flat surface in the engine compartment near the trim tab actuators (typically on the inboard side of the transom or on a bulkhead near the transom). The mounting bracket (Bennett part 219-H1179) is sold separately. The hydraulic lines from the HPU to the actuators run through the engine compartment with proper supports, and the wiring runs from the HPU to the helm switch through the standard accessory wiring chase.

Wiring is straightforward: 12V positive feed (with appropriate fuse, typically 20-30 amps depending on overall system size), 12V ground, and the two switched control inputs from the helm switch (one for tab-up, one for tab-down). The HPU's control inputs are internally protected against incorrect wiring sequence so a wiring mistake at install won't immediately damage the unit.

Replacement HPU for older Bennett systems. If you're replacing a failed older Bennett HPU on an existing trim tab system, the V351HPU1 is the current-generation replacement. The hydraulic line fittings and wiring connections match the older Bennett HPUs so the swap is essentially direct: drain the old HPU, disconnect the lines and wiring, mount the new V351HPU1 in the same location, reconnect the lines and wiring, refill with fresh ATF, bleed the system, and you're back in business. Total swap time is typically 1-2 hours.

What's in the box. The V351HPU1 unit (with pump, two solenoid valves, reservoir, and Lexan cover, all factory-assembled). Mounting bracket (Bennett 219-H1179) is sold separately. Hydraulic fluid (automatic transmission fluid) is also sold separately. Hydraulic lines from the HPU to the actuators are sold separately as part of a Bennett hose kit (most typical hose kits ship with new tab system installs).

California Prop 65 warning applies. The HPU's electrohydraulic components contain materials that California has classified as reproductive harm chemicals. The warning is a state-of-California legal requirement, not a unique-to-this-product safety issue.

Bennett Marine warranty applies. Same-day shipping before 3 PM ET on in-stock units.