How Pressure Vacuum Relief Valves Work

A Pressure Vacuum Relief Valve (PVRV) is a low-pressure safety device installed on atmospheric storage tanks to protect against overpressure and vacuum conditions that could cause structural failure. Unlike conventional pressure relief valves designed for high-pressure vessels, PVRVs operate at very low pressures — typically 0.5 to 3.5 kPa (2 to 14 inches water column) above or below atmospheric.

The valve uses a weight-loaded or spring-loaded pallet system that opens when the pressure differential exceeds the set point. When tank pressure rises above the set point (during filling or thermal expansion), the pressure pallet lifts, allowing vapor to vent to atmosphere. When tank pressure drops below atmospheric (during pump-out or thermal contraction), the vacuum pallet opens, allowing air to enter and prevent tank implosion.

Modern PVRVs feature low-leakage diaphragm seals (PTFE or FEP) that minimize fugitive emissions during normal operation. The API 2000 standard defines the venting capacity requirements that PVRVs must meet, including thermal breathing, liquid displacement, and emergency fire exposure scenarios.

主要技術規格

應用

• Atmospheric Storage Tanks: Crude oil, gasoline, diesel, jet fuel, chemicals (API 650 tanks)
• Low-Pressure Vessels: Process vessels operating near atmospheric pressure
• Breathing Loss Control: VOC emission reduction through low-leakage seals
• Cold-Climate Service: Heat-traced models for ice prevention at -40 to -50 C ambient

Certifications & Standards

Wanan PVRVs are designed per API 2000 7th Edition for venting capacity, with set pressure accuracy per API 2000 Section 4. Body and pallet components are manufactured from 316L stainless steel with guaranteed low-temperature impact properties (down to -50 C). EAC and GOST R certifications are available for CIS market installations. Optional ATEX certification is available for Zone 1/2 explosive atmosphere installations.