Free Vents

Open tank breathing with weather and debris protection.

What It Is & How It Works

Free vents are open-flow tank fittings that allow unrestricted atmospheric breathing at a tank nozzle while preventing rainwater, debris, insects, and wildlife from entering the tank interior. They serve tanks that store non-volatile or low-hazard liquids where emissions control and pressure/vacuum setpoint management are not required, but where the tank must still breathe freely during filling, emptying, and thermal changes.

A free vent mounts directly to the tank roof nozzle and provides an open flow path between the tank vapor space and atmosphere. Internal baffles or weather hoods deflect rain and snow away from the opening. Screen elements block debris, insects, and birds. Unlike conservation vents, free vents impose no pressure or vacuum setpoint, the tank breathes at essentially atmospheric pressure at all times.

Free vents are sized to match the tank nozzle and the required breathing rate during maximum filling or emptying operations. Material selection, carbon steel or aluminum, depends on the stored product and the external environment. Where a tank is later reclassified to store a volatile product, the free vent must be replaced with a conservation vent or pressure/vacuum vent.

Free Vent vs. Conservation Vent

A conservation vent controls tank breathing through calibrated pressure and vacuum pallets that open at defined setpoints, reducing evaporative emissions and maintaining a slight positive pressure in the vapor space. A free vent provides no pressure or vacuum control, the tank breathes openly to atmosphere. Choose a conservation vent when the stored product is volatile or emissions regulations apply. Choose a free vent when the product is non-volatile and unrestricted breathing is acceptable. Free vents breathe; conservation vents control.

When to Specify Free Vents

Free vents are specified when a tank requires atmospheric breathing with weather protection but does not require pressure/vacuum control or emissions management:

Water and Non-Volatile Liquid Storage Tanks storing raw water, process water, brine, or other non-volatile liquids where no evaporative emissions regulations apply and unrestricted breathing prevents vacuum collapse during pump-out.
Agricultural and Irrigation Tanks Above-ground storage for irrigation water, liquid fertilizer, or non-hazardous agricultural liquids where open breathing is acceptable and debris protection is the primary requirement.
Wastewater Equalization and Holding Tanks Equalization basins, holding tanks, and non-hazardous wastewater vessels where the tank must breathe freely during variable fill and draw cycles.
Temporary or Construction-Phase Storage Temporary tanks and construction-site storage where a simple weather-protected opening is sufficient until permanent tank fittings are installed.
Low-Hazard Industrial Process Tanks Process tanks storing non-volatile intermediates or finished products where the stored material does not generate regulated vapor emissions under normal operating temperatures.

Why Shand & Jurs Free Vents Excel

Tanks Requiring Maximum Breathing Capacity

Free vents impose no flow restriction from pressure or vacuum pallets, providing the highest possible breathing rate for a given nozzle size during rapid filling or emptying operations.

Non-Volatile Service Where Emissions Control Is Unnecessary

For tanks storing water, brine, or other non-volatile liquids, a free vent provides the necessary weather and debris protection without the cost and maintenance of a conservation vent mechanism.

Installations Where Simplicity Reduces Maintenance

With no moving parts, setpoint adjustments, or sealing surfaces to maintain, free vents require only periodic screen inspection, reducing the maintenance burden compared to pressure/vacuum devices.

Environments Where Debris and Wildlife Ingress Is a Concern

Internal screens and weather hood designs prevent insects, birds, leaves, and windblown debris from entering the tank through the breathing opening, protecting product quality and downstream equipment.

Applications Requiring Corrosion-Resistant Construction

Available in carbon steel and aluminum configurations to match the external environment and stored product, maintaining long-term performance in coastal, humid, or chemically exposed installations.

What to Consider Alongside Free Vents

Volatile or Flammable Liquid Storage The stored product generates regulated vapor emissions or the tank requires pressure/vacuum setpoint control. See Conservation Vents & Seals.
Fire-case Overpressure Protection The tank requires large-volume emergency relief during fire exposure in addition to normal breathing. See Emergency Vents & Manway Covers.
Flame Protection at the Vent Opening The tank vapor space contains flammable vapors and the vent opening must prevent external flame ingress. See Flame & Detonation Arresters.
Tank-level Monitoring for Non-volatile Storage Pair free vents with L&J Technologies level gauges or float and tape transmitters to provide inventory visibility on water, brine, or process liquid tanks that breathe through open vents. See Clairvoyance.
Future Upgrade Path to Emissions-controlled Breathing Free vents mount to standard tank nozzles. If the tank is later reclassified for volatile service, the free vent can be replaced with a conservation vent on the same nozzle without modifying the tank roof. See Conservation Vents & Seals.