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Pressure & Vacuum Relief Valves

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Elmac Technologies RV1 pressure vacuum relief valve
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Pressure & Vacuum Relief Valves
(Breather Valves, Conservation Vents)

Weight or Spring-Loaded Pressure/Vacuum Relief Valves


Direct acting pressure/vacuum relief valves (also known as breather valves, conservation vents, or safety vents) are low pressure devices specifically designed to protect tanks, process systems and equipment from excessive pressure and vacuum.

As well as providing the primary layer of protection for tanks and process systems, pressure/vacuum valves also minimise emission losses of gases or vapours, thus protecting the environment and providing significant financial savings.

The range includes pressure only, vacuum only and combined pressure/vacuum valves, all available with flanged outlets or vented to atmosphere.

Pressure / vacuum relief valves are used extensively on bulk storage tanks, including fixed roof tanks with floating covers, to minimise evaporation loss. The valves prevent the build up of excessive pressure or vacuum which can unbalance the system or damage the storage vessel.

Pressure and vacuum protection levels are controlled with weighted pallets or springs and can be combined to provide the required pressure/vacuum settings. It is common to combine pallet and spring systems in one unit i.e. pressure settings require a spring section, whilst the vacuum settings use the pallet method.

Pressure & Vacuum Relief Valve Design Series

Please click the image of the design series you require for more detailed product information.

RV1 Series - Pressure & Vacuum to Atmosphere

Elmac Technologies - RV1 Pressure and Vacuum Relief Valves to Atmosphere


RV2 Series - Pressure & Vacuum Piped Away

Elmac Technologies - RV2 Pressure and Vacuum Relief Valves Piped Away


PR1 and PR2 Series - Pressure-Only Relief Valves

Elmac Technologies - PR1 and PR2 Pressure-Only Relief Valves


VR1 and VR2 Series - Vacuum-Only Relief Valves

Elmac Technologies - VR1 and VR2 Vacuum-Only Relief Valves

Principle of Operation

RV1 pressure relief valve flow diagram

Elmac pressure/vacuum relief valves have weight-loaded or spring-loaded pallets. Flow through the valve is controlled by the weight of the pallet or the spring force acting on the pallet to keep the device closed.

Once the pressure or vacuum in the tank reaches the pallet closing force, the pallet will start to lift off the seat and allow flow through the valve.

Due to its air-cushioned sealing technology, Elmac valves prevent emission losses until very close to the set pressure, and prevents air intake until very close to the set vacuum.

The geometry of the valves has been developed in order to optimise overall performance in terms of high flow capacity, set pressure, sealing and re-sealing.

The modular nature of Elmac's valves means they can be tailored to meet specific customer requirements: whether this is pressure or vacuum-protection only; or vapours and gases either piped-away or vented to atmosphere.

A weatherhood protects the pressure vent port and a mesh screen is fitted to prevent intrusion of foreign matter into the valve.

Features & Benefits

  • Pressure / vacuum relief valves provide high flow capacity from a compact valve size
  • Wide range of pressure and vacuum settings to provide maximum tank protection whilst ensuring minimum gas loss
  • Designed and manufactured to API Std 2000 / ISO28300
  • Superior sealing meets the stringent demands of emission control regulations
  • Exceeds seat leakage requirements of API Std 2000 or ISO28300
  • No measurable leakage below 90% of the set pressure, less than 1 SCFH at 90% of the set pressure
  • Low leakage minimises evaporation loss
  • Economic savings due to reduced product loss
  • Alternative connection types available on request
  • Stem/pallet proximity switches available
  • Valve sizing service assists optimum valve performance / cost specification
  • Elmac technical support

Quick Links:

Pressure/Vacuum Relief Valve Data Sheet (in data centre)
Tank & Vessel Protection Equipment
Elmac Expertise
Customer Services