Function and working principle of a breather valve

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I. Function of the breather valve: The breather valve acts as the “nose” of the storage tank. When the pressure inside the tank is too high, it releases air; when the pressure is too low, it draws in air. Under normal conditions, it remains completely sealed, preventing leaks, loss of odor, and waste of the medium. Its function is to protect the storage tank from collapsing or bursting, while also reducing losses due to oil evaporation. II. Working Principle
The breathing valve consists of only two valve discs and two springs/weights: a positive-pressure valve (exhalation valve) and a negative-pressure valve (inhalation valve).

1. Exhalation (when pressure inside the tank is high)
Scenario: Oil collection, feeding. Temperature rises, causing the liquid to expand; exposure to direct sunlight also contributes to this.
Process: Pressure inside the tank increases → pushes open the positive-pressure valve → gas is released from the tank → pressure drops → the valve closes automatically.

2. Inhalation (when pressure inside the tank is low)
Scenario: Oil delivery, discharging. Temperature drops; cooling at night causes contraction.
Process: Pressure inside the tank decreases (creating negative pressure) → atmospheric pressure pushes open the negative-pressure valve → air enters the tank → pressure returns to normal → the valve closes automatically.

3. Normal state
Both valves are tightly closed, maintaining a slight positive or negative pressure inside the tank, preventing it from being in contact with the atmosphere. III. Structure of the breathing valve
Internal components:
– Positive pressure disc – controls exhaust
– Negative pressure disc – controls inhalation
– Positive pressure spring/weight – sets the opening pressure
– Negative pressure spring/weight – sets the vacuum level at which it opens

External components:
– Top: rain cover
– Bottom: flange for connecting to the tank top
Some models come equipped with a flame arrestor layer (flame-arresting breathing valve) to prevent external flames from entering the tank.

IV. Key parameters (must be understood on-site)
1. Positive pressure setting (exhaust pressure)
Common values: +300 Pa, +1500 Pa; exhaust occurs only when the pressure inside the tank exceeds these values. 2. Negative pressure setting (suction vacuum level): Common values are -30 Pa, -50 Pa, and -100 Pa; suction occurs when the negative pressure inside the tank falls below these values. Note: The negative pressure value is very low, and the storage tank is thin and easily deflated; therefore, the vacuum valve is highly sensitive to changes in negative pressure. V. Logic Related to On-site Operation
1. Relationship with liquid level:
Rising liquid level → Volume compression → Increased pressure → Exhalation
Falling liquid level → Increased space → Decreased pressure → Inhalation

2. Relationship with temperature:
Hot weather during the day → Liquid expansion → High pressure → Exhalation
Cold weather at night → Gas contraction → Low pressure → Inhalation

3. Relationship with safety:
Faulty breathing valve → Tank deflation/bulging deformation
Breathing valve stuck and unable to allow inhalation → Vacuum inside the tank during discharge → Equipment damage
Breathing valve stuck and unable to allow exhalation → Overpressure during filling → Danger

VI. Common Faults of Breathing Valves
1. Continuous air leakage with hissing sounds
Causes: Dirty or contaminated sealing surfaces on the valve disc, coking, crystallization; aged, damaged, or deformed gaskets; valve disc stuck and unable to close properly
Symptoms: Continuous leakage and constant hissing
Consequences: Oil and gas leakage, safety hazards, environmental issues

2. Complete failure to function (most dangerous)
Causes: Valve disc frozen, stuck, or rusted; spring stuck; blockages caused by contaminants
Symptoms: No exhaust during filling, no inhalation during discharge
Consequences: Tank deflation or bulging deformation; severe safety accidents may occur

3. Frequent activation and noise (temperature-sensitive)
Causes: Too low positive pressure setting; high vaporization inside the tank; direct sunlight exposure; pressure inside the tank reaching the critical opening point
Symptoms: Noise occurs when it’s hot, stops when cooled down

4. Abnormal inhalation (only exhalation, no inhalation)
Causes: Negative pressure valve disc stuck; negative pressure valve frozen
Symptoms: High negative pressure inside the tank during discharge, but the breathing valve does not allow inhalation
Consequences: Tank is prone to deflation

5. Abnormal exhalation (only inhalation, no exhalation)
Causes: Positive pressure valve disc stuck; foreign objects blocking inside the valve
Symptoms: Overpressure inside the tank during filling, no exhaust
Consequences: Risk of overpressure in the tank

6. Freezing and failure in winter
Causes: Water vapor freezing → Valve disc freezing
Symptoms: Complete failure to function in winter
Consequences: Total loss of functionality

7. Blockage of the flame arrestor layer (breathing valves with flame arrestors)
Causes: Oil stains, coke, or contaminants blocking the flame arrestor mesh
Symptoms: Poor breathing function, unstable tank pressure
Consequences: The breathing valve becomes ineffective

8. Leakage at the flange or connection points
Causes: Damaged gaskets, loose screws
Symptoms: Leakage from the bottom of the valve body
Consequences: Oil and gas leakage