The Difference between Nozzle and Silent Check Valves -

The Difference between Nozzle and Silent Check Valves

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Why a Nozzle Check Valve Can Be a Silent Check Valve, but a Silent Check Valve Cannot Be a Nozzle Check Valve

Terminology:

Check Valves: Check Valves, often referred to as Non-Return Valves, prevent reverse flow. Historically, Non-Return Valves were synonymous with Reflux Valves.

Nozzle Check Valves: These Co-Axial Check Valves utilize the Venturi Principle to minimize headloss and are spring-loaded to mitigate waterhammer.

Silent Check Valves: Also Co-Axial Check Valves, Silent Check Valves are spring-loaded for rapid closure but tend to have higher headlosses.

Introduction

A well-designed Check Valve is crucial in pressurized pipeline systems to safeguard pumps from reverse flow and pipelines from waterhammer. Cost-effectiveness and low headloss are essential for optimal operation.

The rising popularity of Nozzle and Silent Check Valves is attributed to their Non-Slam characteristics, benefiting surge and waterhammer protection strategies.

Although these valves share a Co-Axial design, their different construction impacts the overall lifecycle costing of pipelines.

Check Valve Slam

Check Valve slam occurs when the valve closes suddenly due to flow reversal, causing damaging transients. To avoid this, the design of the Check Valve plays a crucial role.

System Design

• Pump Inertia: Lower angular momentum increases the likelihood of Check Valve slam.
• Pipeline Profile: A higher static head versus dynamic head raises the potential for slam.
• Pipeline Diameter: Larger diameters extend the travel time for the Check Valve disc, increasing slam risk.
• Parallel Pumping: Rapid flow reversal in the common pump header causes slamming.
• Column Separation: Rapid flow reversal results in high-pressure transients.
• Surge Vessels: These devices can prompt quick flow reversal, enhancing slam risk.
• Constant Speed Pumps: Unlike variable speed drives, these pumps can't be ramped up or down, and have low inertias.

Valve Design

Effective Check Valve designs must ensure rapid closure, with short travel distances and low inertia. Both Nozzle and Silent Check Valves feature these characteristics, aiding in the prevention of waterhammer.

For more details, visit nozzle check valve manufacturers.

Nozzle Check Valves vs. Silent Check Valves

Both valve types are characterized by linear closing, spring-loaded designs with short closing strokes, reducing the potential for waterhammer.

Since the 1990s, awareness about waterhammer has grown, boosting the popularity of these valves in the South African Water Industry.

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Headloss Characteristics

Nozzle Check Valves operate on the Venturi principle, ensuring low headloss, while Silent Check Valves, lacking a diffuser, generate higher headlosses.

Face-to-Face Dimensions

Nozzle Check Valves often feature shorter face-to-face dimensions, aiding in compact design layouts.

Initial Cost vs. Life Cycle Costing

While Nozzle Check Valves may have higher initial costs, their lifecycle benefits often outweigh the price difference. Manufacturers like REXUS focus primarily on water industry applications, making the cost differential negligible when lifecycle benefits are considered.

Spot the Difference

To differentiate between Nozzle and Silent Check Valves, consider:

• Flow Recovery: Venturi designs indicate Nozzle Check Valves.
• Diffusers: The presence of a diffuser suggests a Nozzle Check Valve, provided it supports flow recovery.

Conclusion

Both valve types efficiently minimize waterhammer, but Nozzle Check Valves offer superior performance and shorter face-to-face dimensions. Distinguishing between the two is vital for optimal pipeline lifecycle costing.

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