Part Number: ZWD4040G-K
Category: Pressure Washer Pumps → Triplex Pumps → Gas Pressure Washer Pumps
Type: Comet ZWD4040G-K Pressure Washer Pump with Unloader – 4.0 GPM 4000 PSI 1" Gas Shaft

The Comet ZWD4040G-K Pressure Washer Pump with Unloader (Part #ZWD4040G-K) is a genuine OEM triplex plunger pump engineered for heavy-duty commercial and industrial pressure washing applications. Manufactured by Comet Pumps, this direct-drive pump delivers 4.0 GPM at 4,000 PSI, providing exceptional cleaning performance for contractors, fleet washing, construction equipment, agriculture, manufacturing facilities, and other demanding cleaning environments.

Key Features & Benefits

• Genuine Comet OEM triplex pressure washer pump
• Part Number: ZWD4040G-K
• Factory-equipped with integrated unloader valve
• Heavy-duty triplex plunger design
• Delivers up to 4.0 GPM at 4,000 PSI
• Designed for gas-powered pressure washers
• 1-inch hollow shaft for direct engine mounting
• Operates at 3,400 RPM
• Compatible with engines up to 14.5 GHP
• 15 mm ceramic plungers for extended durability
• 1/2" FPT water inlet
• 3/8" FPT high-pressure outlet
• OEM-quality construction for demanding commercial applications

Technical Specifications

Part Number: ZWD4040G-K

Pump Model: ZWD4040G-K

Manufacturer: Comet Pumps

Product Type: Triplex Pressure Washer Pump with Unloader

Maximum Flow Rate: 4.0 GPM

Maximum Pressure: 4,000 PSI

Maximum Pump Speed: 3,400 RPM

Gas Horsepower (GHP): 14.5

Shaft Size: 1" Hollow Shaft

Ceramic Plunger Size: 15 mm

Water Inlet: 1/2" FPT

High-Pressure Outlet: 3/8" FPT

Connection Size: 1/2" Inlet / 3/8" Outlet

Weight: 17 lbs

Integrated Unloader: Yes

OEM Replacement: Yes

Compatible Applications

Designed for use with compatible gas-powered pressure washer systems featuring:

• 1-inch horizontal engine shafts
• Direct-drive pressure washer systems
• Engines up to 14.5 GHP
• Commercial pressure washers
• Industrial cleaning equipment
• Fleet washing systems
• Agricultural equipment cleaning
• Construction equipment cleaning
• Equipment replacement and repair projects
• OEM equipment installations

Always verify shaft size, mounting configuration, engine horsepower, and pressure/flow requirements before ordering.

Function of the Pressure Washer Pump

The ZWD4040G-K pump helps:

• Deliver up to 4.0 GPM of water flow
• Generate operating pressures up to 4,000 PSI
• Provide reliable commercial-grade cleaning performance
• Regulate system pressure with the integrated unloader valve
• Protect the pump during bypass operation
• Deliver smooth, efficient continuous-duty performance

Its heavy-duty triplex plunger design provides superior durability, improved efficiency, and longer service life than conventional pump designs.

Common Signs Replacement Is Needed

Replace the pump if you notice:

• Reduced operating pressure
• Decreased water flow
• Water or oil leaks
• Excessive operating noise
• Unloader valve malfunction
• Cracked or damaged pump housing
• Excessive internal wear
• Loss of cleaning performance

Replacing a worn pump restores pressure washer performance while minimizing costly equipment downtime.

Installation & Service Notes

• Shut down the pressure washer and disconnect the spark plug before servicing.
• Relieve all system pressure.
• Verify compatibility with the 1-inch shaft, mounting configuration, engine horsepower, and pressure requirements.
• Install the pump according to the manufacturer's specifications.
• Connect the 1/2" FPT inlet and 3/8" FPT outlet fittings.
• Ensure the integrated unloader valve is properly adjusted according to system specifications.
• Prime the pump with water before startup.
• Verify proper operation and inspect for leaks after installation.

Important: Never operate the pump without an adequate water supply. Running the pump dry can quickly damage the ceramic plungers, seals, valves, and unloader assembly, significantly reducing pump service life.

Maintenance Recommendations

• Check the pump oil level regularly and service the pump according to Comet maintenance schedules.
• Inspect ceramic plungers, packings, water seals, valves, and the integrated unloader valve during routine maintenance.
• Maintain clean, filtered inlet water to minimize internal wear.
• Flush the pump after use when pumping dirty or corrosive water.
• Use only genuine OEM Comet replacement parts and approved lubricants to maintain optimum pump performance, reliability, and long service life.