ST-291 Pressure Washer Unloader Valve 5070 PSI – OEM Replacement Part
Part Number: 6647
Category: Pressure Washer Parts → Unloader Valves → High-Pressure Unloader Valves
Type: Suttner ST-291 Pressure Washer Unloader Valve
The Suttner ST-291 Pressure Washer Unloader Valve (Part #6647) is a heavy-duty OEM replacement pressure-actuated unloader engineered for high-pressure cleaning systems operating up to 8 GPM and an impressive 5,070 PSI. Designed for demanding commercial, industrial, and specialized pressure washing applications, the ST-291 provides precise pressure regulation, dependable bypass operation, and superior pump protection under extreme operating conditions.
Key Features & Benefits
- Genuine Suttner OEM replacement unloader valve
- Rated for pressures up to 5,070 PSI
- Supports flow rates up to 8 GPM
- Pressure-actuated bypass operation
- Heavy-duty commercial and industrial design
- Protects pumps and plumbing components from pressure spikes
- Maintains consistent operating pressure
- Reliable bypass performance
- Durable construction for demanding applications
- Ideal for high-pressure cleaning systems
- Long service life and dependable operation
Technical Specifications
Part Number: 6647
Manufacturer: Suttner
Model: ST-291
Product Type: Pressure Actuated Unloader Valve
Maximum Flow Rate: 8 GPM
Maximum Pressure: 5,070 PSI
Maximum Temperature: 176°F
Inlet Connection: 3/8" FPT
Outlet Connection: 3/8" FPT
Bypass Connection: 1/2" FPT
Operation Type: Pressure Actuated
OEM Replacement: Yes
How the ST-291 Works
The ST-291 automatically regulates system pressure during operation.
When the trigger gun is released:
- Pressure rapidly increases within the discharge system
- The unloader valve activates
- Water is redirected through the bypass circuit
- Excess pressure is relieved
- Pumps and related components are protected
When the trigger gun is reopened:
- Water flow returns to the discharge line
- Cleaning pressure is restored immediately
- Consistent system performance is maintained
This automatic process helps improve equipment longevity while ensuring reliable operation.
Built for High-Pressure Applications
With a maximum pressure rating of 5,070 PSI, the ST-291 is ideal for demanding cleaning tasks such as:
- Surface preparation
- Industrial equipment cleaning
- Heavy equipment maintenance
- Concrete cleaning
- Commercial pressure washing
- Manufacturing facility wash-down
- Oil and gas industry cleaning
- Construction equipment cleaning
Its high-pressure capability allows it to perform reliably in applications where standard unloaders may not be sufficient.
Common Applications
Commercial Pressure Washing
Ideal for:
- Professional contractors
- Fleet washing
- Heavy equipment cleaning
- Property maintenance services
- Surface restoration projects
Industrial Cleaning Systems
Suitable for:
- Manufacturing plants
- Processing facilities
- Industrial maintenance operations
- Construction equipment wash stations
- High-pressure cleaning systems
Performance Benefits
- Reliable pressure regulation
- Improved pump protection
- Reduced pressure spikes
- Stable operating pressure
- Consistent cleaning performance
- Enhanced equipment lifespan
- Commercial-duty durability
- Reduced maintenance requirements
Signs an Unloader Valve Needs Service
Inspect or replace the valve if you experience:
- Pressure fluctuations
- Water leakage
- Inconsistent bypass operation
- Reduced cleaning pressure
- Delayed pressure response
- Excessive wear from long-term use
Installation Notes
- Verify compatibility with system pressure and flow requirements.
- Install using appropriate thread sealant.
- Route bypass plumbing according to manufacturer recommendations.
- Inspect hoses, fittings, and pumps before startup.
- Test pressure regulation and bypass operation after installation.
- Confirm all components are properly rated for high-pressure operation.
Important: Because of the extreme pressure capability of this valve, all system components must be rated for the intended operating pressure to ensure safe operation.
Maintenance Recommendations
- Inspect regularly for leaks and wear.
- Verify smooth bypass function.
- Monitor system pressure during operation.
- Maintain clean inlet water filtration.
- Service or replace worn components promptly.
- Follow Suttner maintenance recommendations.
