3-Way Valve Manifold: Structure, Working Principle & Core Functions

A critical component for differential pressure transmitter systems, the 3-way valve manifold ensures safe, stable, and accurate operation of flow/differential pressure sensors in industrial process pipelines.

What is a 3-Way Valve Manifold?

A 3-way valve manifold consists of three interconnected valves, categorized by their roles in the system:

• High-pressure valve (left side)

• Low-pressure valve (right side)

• Balance valve (middle)

It is exclusively paired with differential pressure transmitters to:

• Connect or disconnect the positive/negative pressure measuring chambers from pressure tapping points

• Isolate or equalize pressure between the positive and negative measuring chambers

Structure & Working Principle

Core Components

A standard 3-way valve manifold comprises:

• Valve body (integrated housing)

• Two globe valves (cut-off function)

• One balance valve (pressure equalization function)

1. Commissioning Procedure for Differential Pressure Transmitters

Follow these steps to safely put the transmitter into operation:

1. Open the two blowdown valves on the differential pressure transmitter

2. Open the balance valve to equalize pressure

3. Slowly open the two globe valves to purge air/contaminants from impulse lines

4. Close the two blowdown valves

5. Close the balance valve – the transmitter is now operational

2. On-Line Zero Calibration

For quick, in-situ zero calibration:

1. Open the balance valve (to equalize pressure across the transmitter)

2. Close the two globe valves (isolate the transmitter from process pressure)

3. Perform zero calibration on the transmitter

3. Role of the Balance Valve

The balance valve is a safety-critical component:

• During commissioning: Kept open to prevent single-cavity overpressure (avoids transmitter damage from excessive pressure spikes)

• During normal operation: Kept closed to ensure accurate differential pressure measurement

4. Full Transmitter Commissioning Process

1. Close all secondary valves

2. Open primary valves

3. Open blowdown valves to flush pipelines (remove debris/air)

4. Close blowdown valves

5. Open the 3-way valve manifold’s balance valve; close positive/negative cavity valves

6. Open positive/negative cavity secondary valves

7. Open the 3-way valve manifold’s positive cavity valve; open blowdown screws on the transmitter’s positive/negative cavities (final purge)

Key Functions of a 3-Way Valve Manifold

The 3-way valve manifold is essential for protecting flow/differential pressure sensors during pipeline startup and operation. Its core applications include:

1. Pressure Surge Protection (Startup)

• When filling an empty pipeline with medium, pressure on the sensor sides changes abruptly

• Action: Close valves A/B (sensor isolation); open bypass valve C (pressure equalization) to prevent sensor damage from excessive pressure differentials

2. Gradual Pressure Equalization

• After the pipeline is full and stable:

• Open either valve A or B to apply pressure evenly to the sensor

• Close valve C and open the remaining valve (A/B) – sensor operates normally

3. Reverse Shutdown Sequence

• Follow the opposite steps to safely shut down the system (protect sensor from pressure shocks)

4. Maintenance Convenience

• Clean process pipelines post-operation without disrupting the sensor (bypass the sensor via the manifold)

• Minimize downtime for pipeline maintenance while keeping the sensor intact