Editorial Technical Reference

Metal tank pressure relief valve assembly: pressure/vacuum breather valve for atmospheric and low-pressure tanks

Pressure/vacuum relief (breather) valves for atmospheric and low-pressure metal tanks · mbar-range settings, API 2000 venting scope, pipe-away outlets, sizes DN 50–300 and seating diaphragms

This page covers the relief valve assembly mounted on the roof nozzle of an atmospheric or low-pressure metal tank: a pressure/vacuum (breather) valve that lets the tank exhale vapour when pressure rises and inhale air when vacuum forms. Ask three things first: the pressure and vacuum settings in mbar and the flow each must pass, whether vapours vent to atmosphere or must be piped away, and which seat material and body material suit the stored product.

Pressure/vacuum relief (breather) valves and assemblies for atmospheric and low-pressure metal storage tanks and road tankers, set from a few millibar up to about 1 barg. Spring-loaded and pilot-operated pressure relief and safety valves for vessels, boilers and process lines are covered on the Pressure relief valve page. Flame arresters on their own, emergency vents and floating-roof seals are outside this page.

CNFX editorial research · Sources checked October 12, 2026 · 4 sources

Set pressure and vacuum Choose the outlet and materials

Illustration of a hooded pressure/vacuum valve with screened vents and a side flange, bolted to a nozzle on the roof of a large storage tank, with other tanks and pipe racks behind — Illustration: pressure/vacuum relief valve on a storage tank roof

Start with your task

Set pressure and vacuummbar settings and API 2000 scope. Choose the outlet and materialsAtmospheric or pipe-away; seats and bodies.

Set the pressure and vacuum relief points

API Standard 2000 (fifth edition, 2009) covers the normal and emergency vapour venting requirements for aboveground liquid petroleum or petroleum products storage tanks and aboveground and underground refrigerated storage tanks designed for operation from vacuum through 15 psig (1.034 bar gauge), including the causes of overpressure or vacuum, determination of venting requirements, means of venting, selection, installation and maintenance of venting devices, and testing and marking of relief devices. The Standard Norge listing shows later editions published in 2013, 2014, 2020 and 2026. [1]

Groth's Model 1200A pressure vacuum relief valve, described as protecting the tank from overpressure or excessive vacuum and reducing evaporation losses from normal tank "breathing", is listed in sizes 2″ (DN 50) to 12″ (DN 300) with pressure settings of 0.5 osig to 15 psig (2.15 mbarg to 1.03 barg) and vacuum settings of 0.5 osig to 7.35 psig (2.15 to 506 mbarg). [2]

Editorial calculation: Groth's 15 psig upper pressure setting equals 1.034 barg, the top of the API 2000 range; a +200 mm water-column setting, as YOY lists for its tanker breather valve, is about 19.6 mbar, and −45 mm water column is about −4.4 mbar. [2] [1] [4]

Give the supplier the tank type and design pressure and vacuum, stored product and vapour, maximum pump-in and pump-out rates, thermal breathing basis, nozzle size and flange standard, and whether a flame arrester is required.

Choose the outlet, seats and body materials

Where vapours must not go to atmosphere, a pipe-away version is used. Groth's Model 1220A has a flanged outlet connection so escaping vapours are piped away, with the same DN 50–300 sizes and 2.15 mbarg to 1.03 barg pressure range and vacuum settings of 2.15 to 827 mbarg (0.5 osig to 12 psig). [3]

For both models Groth lists peripheral and central seat guides, a wide seat with an air-cushion seal for low leakage, a self-draining housing with drip rings to protect seats from condensate and freezing, fluoropolymer seating diaphragms as standard against sticking from resinous vapours and moisture, Buna-N, FKM and other diaphragms as options, bodies in aluminium, carbon steel, stainless steel, fiberglass and other materials, ATEX and PED certification, and 150# ANSI, PN10, PN16 and JIS drilling. [2] [3]

For road tankers, YOY lists the A411XH breathing safety relief valve in DN 80–250, cast steel or stainless steel, with a control pressure of +200 mm water column and −45 mm water column. [4]

Groth 1200A, Groth 1220A and YOY A411XH breather valve settings

Compare settings in the same units and at the same flow basis.

Valve	Settings	Size and features
Groth 1200A (vent to atmosphere)	Pressure 2.15 mbarg–1.03 barg; vacuum 2.15–506 mbarg. [2]	DN 50–300; self-draining housing. [2]
Groth 1220A (pipe-away)	Pressure 2.15 mbarg–1.03 barg; vacuum 2.15–827 mbarg. [3]	DN 50–300; flanged outlet. [3]
YOY A411XH (tanker)	+200 mm / −45 mm water column. [4]	DN 80–250; cast steel or stainless. [4]

Pressure and vacuum pallets, diaphragm seats, housing and outlet of a P/V breather valve

Part	Role	Fix in the order
Pressure pallet and seat	Opens to release vapour at the pressure setting. [2]	Setting and seat material.
Vacuum pallet and seat	Opens to admit air at the vacuum setting. [2]	Setting and seat material.
Seating diaphragm	Fluoropolymer standard; Buna-N, FKM options. [2]	Material for the vapour.
Housing and drip rings	Self-draining; protect seats from condensate and freezing. [2]	Body material.
Outlet	Open hood or flanged pipe-away outlet. [3]	Outlet type and flange.
Inlet flange	150# ANSI, PN10, PN16 or JIS drilling. [2]	Flange standard and size.

Set pressure, relief capacity, connection size and blowdown on the valve data sheet

Field	What it means and published values	Ask the supplier for
Set Pressure (bar)	2.15 mbarg–1.03 barg (Groth); +200 mm water column ≈ 19.6 mbar (YOY). [2] [4]	Pressure and vacuum settings.
Relief Capacity (m³/h)	Venting requirement determined under API 2000. [1]	Flow at the set overpressure.
Operating Temperature (°C)	Vapour and ambient temperatures; Groth lists a steam jacket spacer as an option. [2]	Range.
Connection Size (DN)	DN 50–300 (Groth); DN 80–250 (YOY). [2] [4]	Inlet and outlet sizes.
Back Pressure (bar)	Pressure in the outlet line of a pipe-away valve. [3]	Effect on settings and capacity.
Blowdown Pressure (%)	Overpressure to full lift and reseat.	Values.
Body Material	Aluminium, carbon steel, stainless steel, fiberglass. [2]	Material for the product.
Seat Material	Fluoropolymer standard; Buna-N, FKM. [2]	Seat and diaphragm.
Leakage Rate (mL/min)	Wide seat and air-cushion seal for low leakage. [2]	Leak rate and test.
Response Time (s)	Opening behaviour.	Data if available.
Weight (kg)	Handling on the tank roof.	Weight.
Pressure Rating (bar)	Tank design up to 15 psig (1.034 barg) under API 2000. [1]	Body rating.

Send the tank, product and venting requirements together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Tank: [type; design pressure and vacuum; nozzle size]
Product: [liquid; vapour; temperature]
Flows: [pump-in; pump-out; thermal breathing]
Settings: [pressure mbar; vacuum mbar]
Outlet: [to atmosphere or pipe-away]
Materials: [body; seats]
Other: [flame arrester; certification]

See manufacturer records Send an enquiry through CNFX

Buyer questions

What settings do tank breather valves use?

Groth lists its 1200A at 2.15 mbarg to 1.03 barg pressure and 2.15 to 506 mbarg vacuum; YOY lists +200 mm and −45 mm water column for its tanker breather valve. [2] [4]

Which standard covers tank venting?

API Standard 2000 covers normal and emergency venting of atmospheric and low-pressure storage tanks designed for vacuum through 15 psig (1.034 barg). [1]

When is a pipe-away breather valve used?

Where vapours must be piped away instead of released to atmosphere; Groth's 1220A has a flanged outlet for this. [3]

Sources and what still needs a direct check

Sources checked 2026-10-12. Groth and YOY describe their own valves; the API 2000 scope is quoted from the Standard Norge catalogue listing of the 2009 edition.

Standard Norge — API STD 2000 Venting Atmospheric and Low-Pressure Storage Tanks (5th edition, 2009, abstract and version history) ↗ Standard abstract Return to text ↑
Groth — Model 1200A Pressure Vacuum Relief Valve ↗ Maker product page Return to text ↑
Groth — Model 1220A Pressure Vacuum Relief Valve with pipe-away ↗ Maker product page Return to text ↑
YOY Valve — A411XH Breathing Safety Relief Valve ↗ Maker product page Return to text ↑

Still to check yourself

Fix pressure and vacuum settings in mbar.
Obtain flow capacity at the allowed overpressure.
Choose atmospheric or pipe-away outlet.
Confirm seat and body materials for the product.
Verify the legal supplier and factory.