The Complete Guide to Check Valves

Introduction: What is a Check Valve?

A check valve, also known as a non-return valve (NRV), is a mechanical device that allows fluid (liquid or gas) to flow in one direction only. It prevents reverse flow in a piping system, which is critical in maintaining safe and efficient operation especially in measurement, monitoring, and control systems.

Unlike manually operated valves, check valves are self-acting. They automatically open with forward flow and close when the flow reverses, without the need for external power or human intervention.

Why Are Check Valves Important?

Check valves play a vital role in protecting equipment, maintaining system integrity, and ensuring measurement accuracy. Specifically, they help:

• Prevent backflow that could damage pumps, flow meters, or other instruments
• Maintain pressure stability in closed-loop systems
• Avoid contamination of clean or metered lines
• Ensure safety in gas and chemical systems
• Support automation by providing passive control without active components

In monitoring and control systems, check valves are often paired with sensors, transmitters, flow controllers, and sampling systems, where maintaining unidirectional flow is essential for accurate readings.

How Do Check Valves Work?

The core principle of a check valve is pressure differential. When the upstream pressure exceeds downstream pressure, the valve opens. If the downstream pressure becomes higher, the valve automatically closes.

Key Terms:

Common Applications in Measurement & Control

Check valves are used across industries including water treatment, chemical processing, HVAC, oil and gas, food and beverage, and more. Some common applications include:

• Protecting pressure sensors from reverse flow
• Preventing back-siphonage in sampling systems
• Safeguarding flow meters in gas or liquid lines
• Ensuring directional flow in pump circuits
• Isolating instruments in multi-point monitoring setups
• Maintaining calibration integrity in gas analysers and dosing systems

Types of Check Valves

Each design has its own response time, flow capacity, and suitability for gases or liquids.

Materials & Compatibility

Material choice is critical to ensure chemical compatibility, mechanical integrity, and longevity. Common materials include:

Body Materials:

Stainless Steel: Corrosion-resistant, suitable for most industrial environments

Brass: Economical and widely used for water systems

PVC / CPVC: Lightweight, chemical-resistant for non-metallic pipelines

PTFE / PVDF: Excellent chemical resistance in aggressive media

Seal Materials:

EPDM: Good for water, weak acids

Viton®: Resistant to oils, solvents, and high temperatures

PTFE: Chemically inert, non-stick, high-purity applications

NBR (Buna-N): General-purpose for fuels and oils

Always verify compatibility using chemical resistance charts before selecting a check valve for corrosive or specialized applications.

How to Select the Right Check Valve

Choosing the right check valve depends on several technical and operational factors:

1. Flow Characteristics

Calculate the flow rate (L/min or m³/h)

Check pressure drop tolerance

Consider Cv/Kv values (flow coefficients)

2. Cracking Pressure

Match the valve’s minimum opening pressure to your system’s available differential pressure

3. System Pressure & Temperature

Ensure the valve’s rated pressure and temperature limits suit your system conditions

4. Fluid Type

Is it liquid, gas, slurry, or steam?

Is it clean, abrasive, or corrosive?

5. Installation Orientation

Some valves must be installed vertically or horizontally check manufacturer guidance

6. Maintenance Requirements

Consider accessibility and how frequently the valve may need inspection or replacement

Installation Best Practices

• Follow the flow direction arrow stamped on the valve body
• Avoid installing directly after pumps or elbows where turbulence is high
• Provide straight pipe lengths upstream/downstream when possible
• For vertical lines, ensure the valve is suitable for vertical use
• In gas systems, avoid trapping condensates near the valve
• Periodically inspect for leakage or wear in critical systems

Common Issues & Troubleshooting

Conclusion

Check valves are essential components in ensuring safe, reliable, and accurate operation of measurement, monitoring, and control systems. By choosing the right type, material, and installation method, you can prevent backflow, protect equipment, and maintain precise process control.

At Measure Monitor Control, we offer a wide range of check valves suited for diverse applications from industrial fluid control to high-purity instrumentation.