The primary function of a check valve is to prevent backflow of the medium.

However, in practical engineering, after installation and commissioning, issues such as flow obstruction, abnormal pressure drop, or even backflow may still occur.

 

These problems are generally not caused by valve quality, but by incorrect installation orientation, system operating conditions, or improper valve selection.

Based on field experience, this article outlines common causes and corresponding solutions.

 

1. Check Valves Require Correct Flow Direction

 

The vast majority of check valves are designed to operate correctly in only one fixed direction.

Whether swing, lift, or dual-plate check valves, their internal structures are engineered specifically for unidirectional flow.

 

If the actual flow is opposite to the valve’s design direction, the following issues may occur:

● The valve disc cannot open or opens insufficiently

● Significant increase in system pressure drop

● Vibration or noise generated by the valve

● Failure of the check function, posing a risk of backflow

 

Therefore, any abnormal flow direction must be addressed promptly.

 

2. Common Causes of Abnormal Flow Direction

 

1. Incorrect Valve Body Installation

This is the most frequent cause observed in the field.

Most check valves have a flow direction arrow on the body to indicate the proper flow path of the medium. If this marking is ignored during installation, the valve will not function correctly.

 

Situations prone to errors during installation include:

● Pipe orientation is changed without re-verifying valve direction

● Multiple valves are installed simultaneously, and some are installed backward

● Installation in underground or confined spaces with limited visibility

 

2. Actual Flow Direction Inconsistent with Design

In some systems, the pipeline does not always maintain a single flow direction, for example:

● Switching operation between primary and standby pumps

● Backwashing or backflow conditions in the system

● Short-term reverse flow during start-up or shutdown

If these conditions are not considered when selecting the check valve, abnormal operation may occur in certain phases even if the valve is installed correctly.

 

3. Mismatch Between Valve Type and Operating Conditions

Different types of check valves have specific requirements regarding installation orientation and flow conditions, for example:

● Lift check valves are generally suitable for horizontal installation

● Swing check valves may not fully open at low flow velocities

● Spring-loaded check valves may struggle to open in low-pressure systems

If a valve fails to open smoothly under correct flow direction, it is often mistakenly assumed that the flow is reversed.

 

4. Sticking or Damaged Internal Components

Even with correct installation, check valves may fail to operate properly under the following circumstances:

● Damage to the valve disc during transportation or installation

● Foreign debris entering the valve

● Internal corrosion after long-term inactivity

The typical result is restricted flow and abnormal system pressure drop.

 

3. Recommended Actions When Incorrect Flow Direction Is Detected

 

1. Verify the Valve Body Flow Direction Marking

After shutting down the system, check whether the arrow on the valve body aligns with the actual flow direction.

This is the most direct and efficient method for verification.

If the installation orientation is incorrect, the valve must be reinstalled; there is no reliable temporary solution.

 

2. Confirm the Actual System Operating Conditions

Focus on verifying the following:

● The main flow direction during normal operation

● Presence of reverse flow or operational switching

● Whether bidirectional operation needs to be considered

In complex systems, a single check valve may not be suitable for all operating conditions.

 

3. Reassess Check Valve Selection

If the installation orientation is correct but the problem persists, examine the following:

● Whether the valve type is appropriate for the current flow rate and pressure

● Whether the cracking/opening pressure is too high

● Whether a low-resistance design is required

Many field issues are fundamentally due to improper valve selection rather than installation errors.

 

4. Disassemble and Inspect if Necessary

If the above measures do not resolve the issue, the check valve should be disassembled for inspection, focusing on:

● Whether the valve disc moves smoothly

● Presence of foreign objects or damage

● Condition of the sealing surfaces

This step is essential for critical systems.

 

4. How to Prevent Check Valve Orientation Issues in the Early Stage

 

● Clearly indicate the flow direction of the medium during the design phase

● Consider all possible operating conditions during valve selection

● Verify valve orientation before installation

● Perform water flow or functional testing prior to commissioning

Most orientation-related issues with check valves can be avoided during the early stages.

 

5. Common Questions (Q&A)

 

Q1: Can a check valve installed backward still be used?

It is not recommended. A reversed installation prevents the valve from opening properly and may pose a risk of backflow.

 

Q2: What if the valve body has no flow direction arrow?

Consult the product documentation or confirm with the manufacturer; decisions should not be made based on experience alone.

 

Q3: Can a standard check valve be used if the system has bidirectional flow?

Generally, it is not suitable. Alternative backflow prevention solutions or valves with special designs should be considered.

 

Q4: The flow direction is correct, but the pressure drop is high. Is this normal?

No, it is not normal. This usually relates to valve structure, size, or cracking/opening pressure, and valve selection should be reassessed.