Pressure Conservation Vents

Overpressure relief for blanketed and sealed tanks.

What It Is & How It Works

Pressure conservation vents are weight-loaded relief devices that protect storage tanks from overpressure by releasing vapor when internal pressure exceeds a calibrated set point. They address the hazard of tank shell deformation or roof failure caused by pressure buildup from thermal expansion of the vapor space, product filling operations, or inert gas blanketing system overshoot. Unlike combined P/V conservation vents, pressure-only models contain a single pressure pallet and no vacuum relief mechanism.

The pallet assembly sits on a machined seat at the top of the vent body, held closed by calibrated weights stacked on the pallet carrier. When internal tank pressure exceeds the combined force of the weights and the pallet’s own mass, the pallet lifts off the seat and vapor escapes to atmosphere. When pressure drops below the set point, the pallet reseats under its own weight and the tank returns to a sealed condition. The device cycles automatically with each pressure event.

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

Pressure Vent vs. P/V Conservation Vent

A combined P/V conservation vent provides both pressure and vacuum relief in one device. A pressure-only vent omits the vacuum pallet, relying on a separate device, typically a blanketing valve or dedicated vacuum vent, to handle vacuum conditions. Specify pressure-only when another device already handles vacuum 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 Pressure Conservation Vents

Pressure conservation vents are specified when a tank requires overpressure relief at a dedicated nozzle while vacuum relief is handled separately:

Inert Gas Blanketed Tanks Nitrogen or other inert gas blanketed storage where a blanketing valve provides vacuum makeup and the pressure vent relieves overpressure during filling, thermal expansion, or blanket gas regulator overshoot without wasting blanket gas through an unnecessarily open vacuum path.
Tanks with Separate Vacuum Relief Devices Installations where the vacuum relief function is served by a dedicated vacuum vent or vacuum pilot-operated valve at a different nozzle, and the pressure vent provides independent pressure-only protection at its own nozzle per API 2000 sizing requirements.
Chemical Storage with Directional Vapor Control Tanks where the pressure relief path and vacuum relief path must be routed to different locations, such as vapor recovery for pressure relief and atmospheric intake with a check valve for vacuum relief, requiring separate single-function devices.
Petroleum Storage Subject to EPA 40 CFR 60/63 Fixed-roof tanks where the pressure vent must maintain a vapor-tight seal at all pressures below the set point to minimize fugitive emissions, and where the vacuum function is managed by the tank’s blanketing system rather than a vent pallet.

Why Shand & Jurs Pressure Conservation Vents Excel

Blanketed Tanks Where Blanket Gas Conservation Matters

By providing pressure relief without a vacuum pallet, the vent ensures blanket gas escapes only when overpressure occurs, while the blanketing valve independently maintains the minimum positive pressure needed to preserve the inert atmosphere.

Enhanced Sealing Option

To help reduce emissions during normal operation, Expanda-Seal TM diaphragm ensures no greater than 0.5 SCFH air at 95% of the set point, which increases sealing force as operating pressure approaches the setpoint to help reduce blowdown and vapor loss.

Operations 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 in clean and moderately corrosive vapor environments.

Installations Where Set-Point Adjustment Must Be Fast

Changing the pressure 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 Vapor Recovery Requires a Dedicated Pressure Outlet

When pressure-relieved vapors must be routed to a vapor recovery unit, scrubber, or thermal oxidizer, a dedicated pressure vent provides a single-purpose outlet that can be directly piped to the collection system without routing vacuum air intake through the same path.

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 Pressure Conservation 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 Pressure and Vacuum Conservation Vents.
Tighter Emission Control or Higher Relief Capacity is Needed Pilot-operated pressure 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 Emergency Overpressure Relief for Fire Exposure Pressure conservation vents are sized for normal breathing and pumping loads, not the large-volume relief required during external fire. See Emergency Vents & Manway Covers.
Blanketed Tank Protection System Pair the pressure conservation vent with a blanketing valve for vacuum makeup and blanket gas conservation, a flame arrester at the vent outlet for ignition prevention, and an emergency vent for fire-case protection to create a fully protected blanketed storage tank. See Flame & Detonation Arresters and Emergency Vents & Manway Covers.
Emission Monitoring and Inventory Intelligence Combine pressure conservation vents with L&J Technologies level and temperature instrumentation feeding Clairvoyance to track tank breathing events alongside inventory movements, supporting EPA emission calculations and API 2350 overfill prevention compliance.