Vacuum Vents

Vacuum protection for atmospheric storage tanks.

What It Is & How It Works

Vacuum vents are weight-loaded relief devices that protect atmospheric storage tanks from vacuum collapse by admitting air when internal pressure drops below a calibrated set point. They address the hazard of tank shell buckling or roof collapse caused by vacuum conditions that develop during product withdrawal, vapor condensation from rapid temperature drops, or steam-out cleaning operations. Unlike combined P/V conservation vents, vacuum-only models contain a single vacuum pallet and no pressure relief mechanism.

The vacuum pallet rests on a machined seat inside the vent body, held closed by calibrated weights. When internal tank pressure falls below atmospheric by more than the set point value, atmospheric pressure lifts the pallet against the weight load and air enters the tank. When pressure equalizes, the pallet reseats under its own weight and the tank returns to a sealed condition. The device cycles automatically with each vacuum event, requiring no external power or operator intervention.

Vacuum vents mount on standard tank roof nozzles and are sized per API 2000 for the tank’s maximum in-breathing rate. Set points are adjusted by adding or removing calibrated weights. Construction materials include carbon steel, stainless steel, and aluminum to match stored product vapor characteristics.

Vacuum Vent vs. P/V Conservation Vent

A combined P/V conservation vent provides both pressure and vacuum relief in one device. A vacuum-only vent omits the pressure pallet, relying on a separate device, typically a pressure conservation vent or blanketing valve overpressure path, to handle overpressure conditions. Specify vacuum-only when another device already handles pressure relief at the same tank. For a side-by-side comparison, see the breathing vent selection guide on the Conservation Vents & Seals page.

When to Specify Vacuum Vents

Vacuum vents are specified when a tank requires dedicated vacuum protection at its own nozzle while pressure relief is handled separately:

Inert Gas Blanketed Tanks with Dedicated Pressure Relief Storage tanks where a pressure conservation vent or pilot-operated pressure valve handles overpressure at one nozzle, and a dedicated vacuum vent provides independent vacuum protection at a separate nozzle, ensuring each relief function can be sized, maintained, and documented independently per API 2000.
Tanks Requiring Directional Vapor Path Separation Installations where the vacuum intake path and pressure relief path must be routed through different piping, such as filtered air intake for vacuum relief and vapor recovery for pressure relief, requiring separate single-function devices at dedicated nozzles.
Steam-Out or Cleaning Operations on Fixed-Roof Tanks Tanks subject to periodic steam cleaning where rapid vapor condensation creates severe vacuum conditions that exceed the in-breathing capacity of the primary conservation vent, requiring supplemental vacuum relief through a dedicated vacuum vent.
Petroleum and Chemical Storage Subject to API 2000 Fixed-roof atmospheric tanks where API 2000 sizing calculations indicate separate vacuum and pressure relief devices provide better matched capacity than a single combined P/V vent, particularly on large-diameter tanks with high in-breathing rates.

Why Shand & Jurs Vacuum Vents Excel

Blanketed Tanks Where Each Relief Function Must Be Independent

Separating vacuum relief from pressure relief allows each device to be sized precisely for its function, maintained on its own schedule, and documented individually for regulatory compliance without affecting the other relief path.

Operations Where Vacuum Events Demand High In-Breathing Capacity

A dedicated vacuum vent can be sized to the full in-breathing requirement of the tank without sharing nozzle capacity with a pressure pallet, delivering maximum vacuum relief flow through the available nozzle diameter.

Facilities Requiring Simple, Reliable Mechanical Protection

The single-pallet, weight-loaded design has no moving parts beyond the pallet itself, no springs to fatigue, and no pilot mechanisms to maintain, providing years of reliable service between rebuilds.

Installations Where Set-Point Adjustment Must Be Fast

Changing the vacuum set point requires only adding or removing calibrated weights from the pallet stack, a procedure completed in minutes without tools, without removing the vent from the nozzle, and without breaking the tank seal.

Tanks Where Air Intake Requires Filtration or Conditioning

A dedicated vacuum vent provides a single-purpose air intake point that can be fitted with inlet screens, filters, or desiccant elements to protect stored product quality without routing conditioned air through a shared P/V vent body.

Breathing Vent Configurations — Selection Guide

Attribute	P/V Conservation Vent	Pressure-Only Vent	Vacuum-Only Vent
Primary Function	Provides both pressure and vacuum relief for tanks requiring bidirectional breathing control in a single device	Relieves overpressure only, used where vacuum relief is provided by a separate device or is not required	Relieves vacuum only, used where pressure relief is provided by a separate device such as a blanketing valve
Pallet Configuration	Two independent pallet stacks: one pressure pallet and one vacuum pallet in a common housing	Single pressure pallet stack; no vacuum pallet installed	Single vacuum pallet stack; no pressure pallet installed
Typical Set-point Range	Pressure: 0.5 to 16 oz/sq in.; Vacuum: 0.5 to 8 oz/sq in. (adjustable by weight selection)	0.5 to 16 oz/sq in. pressure relief (adjustable by weight selection)	0.5 to 8 oz/sq in. vacuum relief (adjustable by weight selection)
When to Specify	Default choice for most atmospheric fixed-roof tanks where both pressure and vacuum protection are needed at one nozzle	Tanks with inert gas blanketing where a separate blanketing valve handles vacuum makeup and only pressure relief is needed at this nozzle	Tanks where pressure relief is handled by a dedicated pressure vent or pilot-operated valve at a separate nozzle
Regulatory Driver	API 2000 (combined thermal breathing), EPA 40 CFR 60/63 (emission control), NFPA 30 (flammable liquids storage)	API 2000 (pressure relief sizing), often paired with blanketing valves for nitrogen conservation	API 2000 (vacuum relief sizing), API 650 (tank structural vacuum limits)
Common Pairing	Flame arrester at the vent outlet for ignition prevention; emergency vent for fire-case protection	Blanketing valve for vacuum makeup on the same tank; flame arrester at the vent outlet	Pressure vent or blanketing valve for pressure relief on the same tank
Recommendation	Specify as the standard breathing device for any fixed-roof tank storing volatile or flammable liquids where both pressure and vacuum relief are required	Specify when a separate gas blanketing system provides vacuum makeup and only overpressure relief is needed at the vent nozzle	Specify when pressure relief is handled independently and the tank needs a dedicated, precisely weighted vacuum relief device

What to Consider Alongside Vacuum Vents

The Tank Requires Both Pressure and Vacuum Relief at One Nozzle A combined P/V conservation vent handles bidirectional breathing in a single device, reducing the number of tank roof penetrations and simplifying installation. See Conservation Vents & Seals.
Tighter Sealing or Higher Vacuum Relief Capacity is Needed Pilot-operated vacuum relief valves provide snap-action sealing that eliminates the seat leakage weight-loaded vents allow near the set point. See Pilot-Operated Relief Valves.
The Tank Needs Vacuum Makeup From an Inert Gas Source A blanketing valve admits nitrogen rather than atmospheric air when vacuum develops, preserving an inert atmosphere to protect oxidation-sensitive or moisture-sensitive products. See Tank Blanketing & Vapor Recovery.
Complete Atmospheric Tank Protection Assembly Pair the vacuum vent with a pressure conservation vent for overpressure relief, a flame arrester at each vent outlet for ignition prevention, and an emergency vent for fire-case protection to create a fully protected atmospheric storage tank. See Flame & Detonation Arresters and Emergency Vents & Manway Covers.
Inventory Intelligence and Breathing Event Correlation Combine vacuum vents with L&J Technologies level and temperature instrumentation feeding Clairvoyance to correlate vacuum relief events with product withdrawal rates, supporting operational analysis and API 2350 overfill prevention compliance.