Understanding Wet Kits: What They Do and Why You Might Need One

Key Takeaways

A wet kit (also called a hydraulic wet-line system) powers dump trucks, roll-offs, and lowboy trailers by converting engine power into hydraulic pressure.

The three main configurations—single-line, dual-line, and three-line wet kits—serve different applications depending on flow, pressure, and hydraulic return needs.

The right wet kit increases productivity, safety, and system longevity in any vocational or heavy-haul operation.

What Is a Wet Kit?

A wet kit—short for wet-line kit—is a hydraulic system installed on a truck that powers external equipment such as dump trucks, roll-offs, or detachable trailers. Instead of depending on a separate engine, the system uses the truck’s own power take-off (PTO) to run a hydraulic pump that moves pressurized fluid through hoses to perform heavy lifting, tilting, or pulling tasks.

If your truck hauls or operates hydraulic-driven equipment, a wet kit is the link between your engine’s mechanical energy and your trailer’s hydraulic function. Without one, a dump truck couldn’t raise its bed, a roll-off couldn’t tilt its container, and a lowboy couldn’t detach or reattach its gooseneck.

Main Components of a Wet Kit

Every wet kit has three essential parts:

1. Power Take-Off (PTO):
2. The PTO mounts to the transmission and transfers engine power to the hydraulic pump. When engaged, it begins rotating the pump to create hydraulic pressure.
3. Hydraulic Pump:
4. This is the heart of the wet kit. It converts mechanical energy from the PTO into fluid movement. Pump types—gear, vane, or piston—are chosen based on the system’s pressure and flow requirements.
5. Reservoir and Valves:
6. The hydraulic tank stores and cools the oil before it cycles back into the system. Valves control direction, flow rate, and system pressure, ensuring smooth operation.

Supporting components include filters, return lines, and hoses—all of which must be sized and installed correctly to handle the system’s pressure and prevent failure.

How a Wet Kit Works

When the PTO engages, it drives the hydraulic pump, which draws oil from the tank. The pump pressurizes the oil and sends it through hoses to the equipment—such as the lift cylinder on a dump truck or the tilt mechanism on a roll-off.

Once the work is done, the oil returns to the reservoir to cool before cycling again. The constant flow of pressurized fluid is what allows heavy-duty equipment to operate efficiently and safely.

Types of Wet Kits

Not all wet kits function the same way. The right setup depends on how your truck or trailer uses hydraulic pressure and where the oil flows when the equipment isn’t operating.

Let’s break down the three main configurations and where each one fits best:

1. Single-Line Wet Kit

How it works:

A single-line wet kit uses one pressure hose that carries oil from the truck to the trailer. When the dump body lowers, the hydraulic oil returns to the truck through gravity—there’s no dedicated return line.

Best for:

• End-dump trucks and trailers
• Short-cycle, low-frequency applications

Advantages:

• Simple and cost-effective design
• Fewer hoses and fittings to maintain
• Works well for gravity-down dump applications

Limitations:

Because oil returns slowly and only by gravity, this system can run hotter and may not be ideal for long or frequent dump cycles. It’s best suited for lighter-duty or regional dump truck operations where speed and cycle time aren’t critical.

2. Dual-Line Wet Kit

How it works:

A dual-line wet kit uses two hydraulic hoses—one for pressure and one for return. The oil is pumped to the dump trailer through the pressure line, and it returns directly to the tank through the second hose.

Best for:

• Heavy-duty dump trucks and end-dump trailers
• Operators running frequent dump cycles
• Fleet or vocational work requiring efficiency

Advantages:

• Faster dump cycles
• Lower operating temperatures
• Reduces oil aeration and extends pump life

Limitations:

Requires more plumbing and slightly more installation cost, but the performance and longevity benefits far outweigh the added complexity.

For most dump trucks and vocational setups, the dual-line wet kit is the ideal choice—it’s durable, efficient, and balances simplicity with performance.

3. Three-Line Wet Kit

How it works:

The three-line system adds a dedicated return line from the valve to the tank, separate from the pump suction line. This allows oil to return freely to the reservoir without backpressure, which is critical for continuous or high-flow hydraulic operations.

Best for:

• Lowboy and detachable gooseneck trailers
• Walking floor or live-floor trailers
• Blower systems, winch trucks, and oilfield equipment
• Any application requiring high flow or continuous operation

Advantages:

• Keeps oil cooler during extended use
• Prevents pump cavitation and reduces wear
• Allows faster and smoother operation in demanding hydraulic systems

Limitations:

Slightly more complex and space-demanding due to the third line, but essential for operators who run equipment continuously or at high hydraulic loads.

At Forge Truck Centers, we recommend three-line systems for customers operating lowboys, live-floors, or oilfield winch trucks—where uptime and performance are mission-critical.

Choosing the Right Wet Kit for Your Truck

When selecting a wet kit, several factors must align:

1. Truck Application: Start with how the truck is used. A dump truck may only need a dual-line system, while a detachable trailer may require a three-line setup.
2. Pump Flow & Pressure: Flow (measured in gallons per minute) determines how fast the equipment operates. Pressure (PSI) determines how strong the lift or movement is. Your pump must match your trailer’s hydraulic specs.
3. Reservoir Size: Tanks must hold enough oil for the entire hydraulic circuit, including lines and cylinders. A general rule is one gallon of oil for every gallon per minute of pump flow.
4. PTO Speed Ratio: The PTO must spin the pump at the proper speed. Too fast leads to heat and cavitation; too slow leads to sluggish operation.
5. Mounting and Routing: Space, vibration, and heat dissipation all play a role in how well a wet kit performs long-term.

Forge’s technicians can evaluate your specific truck, trailer, and workload to build the correct wet kit configuration—customized for your real-world operation.

Why the Right Setup Matters

Hydraulic systems are unforgiving. An undersized pump, mismatched PTO, or improper reservoir can lead to inefficiency or even catastrophic failure. Choosing the correct wet kit ensures:

• Consistent hydraulic pressure for faster dump cycles
• Reduced wear and heat buildup, extending component life
• Better fuel efficiency through optimized pump load
• Improved safety with stable hydraulic control

At Forge Truck Centers, our service teams verify every wet-kit installation using flow and pressure testing to confirm that the system performs correctly before the truck ever leaves the lot.

Maintenance Tips for Wet Kits

Like any hydraulic system, wet kits need consistent maintenance. Here’s how to keep yours running at peak performance:

1. Inspect Fluid Regularly:
2. Check oil levels before and after major hauls. Milky or dark fluid indicates contamination or heat damage.
3. Replace Filters:
4. Clean oil keeps pumps and valves alive. Replace return filters every 500 hours or as recommended.
5. Inspect Lines and Fittings:
6. Look for leaks, fraying, or rubbing points. A small leak can lead to major downtime.
7. Monitor Temperature:
8. If the reservoir or hoses are hot to the touch after short use, the system could be over-pressurized or the oil flow restricted.
9. Exercise the System Monthly:
10. If the truck sits idle, run the PTO and operate the hydraulics occasionally to keep seals lubricated.

Signs Your Wet Kit May Need Attention

• Slower dump cycles or trailer movement
• Unusual whining or vibration from the pump
• Oil leaks or aeration in the reservoir
• Excessive heat in the hydraulic lines
• Loss of pressure or erratic operation

If you experience these, don’t ignore them—early diagnosis prevents pump damage and costly downtime.

Installing a Wet Kit on a Used Truck

Many of Forge Truck Centers’ customers purchase used trucks and add wet kits after the sale. Whether you need a single-line setup for a dump truck, a dual-line for regional hauling, or a three-line system for heavy-haul operations, our technicians can install and calibrate everything in-house.

Each installation includes:

• Proper PTO matching
• Correct reservoir sizing
• Heat and return-line routing
• Leak testing and pressure verification

This ensures your truck leaves Forge ready to work hard from day one.

Why Operators Trust Forge Truck Centers

Forge Truck Centers isn’t just a truck dealership—we’re an operational partner for vocational professionals who need equipment that performs under pressure. With locations in Texas, Illinois, and South Carolina, our facilities handle complete hydraulic installations when added to your truck purchase.

From spec’ing new PTOs to diagnosing hydraulic heat issues, our team ensures every component of your wet kit is engineered to deliver the reliability your business depends on.

Wet kits may not get the spotlight, but they’re the unsung heroes of the trucking world. They power the lifeblood of every vocational truck that lifts, tilts, or pulls.

Choosing the correct wet kit—whether a simple single-line for dump trucks or a heavy-duty three-line for detachable trailers—can make the difference between an efficient operation and costly downtime.

At Forge Truck Centers, we help truck owners and fleet operators spec, install, and maintain wet kits that meet real-world demands. Because when your hydraulics work flawlessly, your business runs smoother.

Ready to install a wet kit on your next commercial vehicle purchase?

Visit ForgeTruckCenters.com or call 877-382-0070 to speak with our team.