HAMMER Training Part 9: Surge Protection using Tanks and Valves Part 2

Air Valves in Pipeline Systems

Overview of Air Valves

• Air valves are commonly used in thin-walled pipelines, especially in terrains with local high points to release accumulated air bubbles.

• When pressure drops below zero (e.g., during an emergency pump shutdown), air valves open to allow air inflow, which is crucial for maintaining water column movement.

Managing Transient Effects

• It's important to control the rate at which air is expelled; rapid expulsion can lead to severe transients that may be worse than the initial issue being mitigated.

• The outflow orifice must be sized smaller than the inflow to cushion the effect and prevent problematic collapses of air pockets.

Functionality of Triple Acting Air Valves

• A triple acting air valve features a mechanism that initially releases air quickly but then throttles the outflow as water rises, reducing shock from slamming water columns.

Limitations and Considerations

• While air valves help manage local pressures at high points, they may not protect against negative pressures elsewhere due to terrain topology and wavefront shape.

• Understanding surge wave behavior through animation can clarify why some installations still experience negative pressure despite having air valves.

Modeling and Simulation Insights

Importance of Simulation Tools

• The speaker references sample files included with Hammer software that demonstrate various elements and scenarios relevant to pipeline modeling.

Observing Wave Behavior

• An example simulation shows how a pump shutdown affects pressure dynamics, highlighting the role of an air valve located at a high point in managing transient events.

Analysis of Pressure Dynamics

• As waves travel through the system, their angle impacts how effectively an air valve can mitigate pressure drops; even with an open valve, surrounding topography can lead to negative pressures downstream.

Reflection and Combination of Waves

• The interaction between waves reflects off terrain features, demonstrating complex behaviors where even minor changes can result in significant pressure variations throughout the system.

Understanding Wavefront Behavior and Air Valve Dynamics

Wavefront Reflection and Pressure Dynamics

• The wavefront reflects off the end, creating a dip that reaches ground elevation before meeting the air valve, illustrating complex wave behavior.

• Animating profiles is suggested as an effective method to visualize wave reflections and understand negative pressure occurrences in the system.

• A double-acting air valve experiences an upsurge when pressure returns, caused by adjacent water columns colliding, which can lead to potential issues downstream.

• Emphasizing the importance of animating profile paths helps clarify transient envelopes between maximum and minimum pressures in hydraulic systems.

Air Valve Placement and System Configuration

• Air valves are typically placed at local high points along pipelines to release accumulated air bubbles, crucial for maintaining system integrity.

• In scenarios where air valves are removed for analysis, simply deleting them disrupts pipeline continuity; alternative methods must be employed to simulate their absence.

Active Topology Feature in Modeling

• The active topology feature allows users to designate elements as inactive without deleting adjacent pipes, facilitating scenario comparisons with or without air valves.

• Two methods exist for modeling scenarios: using bypass lines around active air valves or employing tee configurations for easier management of inactive elements.

Entering Opening Sizes and Performance Data

• Users can input opening sizes either as orifice diameters or through airflow curves based on manufacturer data, enhancing accuracy in simulations.

• It's essential to differentiate between pipeline pressure (inside the pipe) and trapped air pressure when entering airflow rates into the model.

Analyzing Air Valve Performance Over Time

• An example model demonstrates tracking various parameters over time during pump shutdown events, including volume of air inside the valve and flow rates.

• Detailed reports provide insights into surge tank dynamics alongside air valve performance; results can be exported for further analysis in software like Excel.

Air Valve Calculation Methods

Overview of Air Flow Calculation Methods

• The video discusses two methods for defining the openings of air valves: using orifices or an air flow curve based on manufacturer data.

• It introduces a library with default values for free air flow rate versus line pressure, clarifying that "free air flow rate" refers to the airflow at atmospheric pressure.

• If manufacturer data is unavailable, users can utilize a default method by specifying an equivalent circular orifice diameter for calculations.

• The system computes relationships from the air flow curve, allowing users to determine airflow rates at specific pressures.

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