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Motherwell Opti-flow 380

Motherwell Opti-flow 380 is a direct-acting pressure/vacuum relief valve range for protecting low-pressure storage tanks against excessive pressure or vacuum. Multiple venting, material and set-pressure configurations support bulk storage, chemical tanks and related process duties. Request a quote for Motherwell Opti-flow 380 from AxFlow.

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Product features

  • Direct-acting pressure/vacuum relief → Protects low-pressure tanks from damaging overpressure and vacuum conditions.
  • Pressure-only, vacuum-only or combined versions → Allows the valve arrangement to match the actual tank-protection duty.
  • Atmospheric or piped-away venting → Supports both open venting and connection to a closed vapour system.
  • DN50–DN300 size range → Covers a broad range of bulk-storage tank breathing requirements.
  • Set pressures from about 2 to 500 mbar → Enables selection for very low-pressure tank protection depending on valve construction.
  • Aluminium, carbon steel and stainless-steel bodies → Provides material choices for different environments and stored products.
  • Opti-flow high-capacity geometry → Provides substantial gas flow from a compact valve size.
  • ATEX and PED compliance where applicable → Supports regulated installations when the correct certified configuration is specified.
  • API 2000 sizing support → Helps match venting capacity to filling, emptying and thermal breathing requirements.
  • Serviceable pallets, diaphragms and seals → Supports inspection, maintenance and lifecycle cost control.

Product description

Bulk storage tanks must breathe as liquid is filled, withdrawn or changes temperature, but uncontrolled venting increases emissions and product loss. Motherwell Opti-flow 380 is a direct-acting pressure/vacuum relief valve, also known as a tank breather valve or conservation vent, constructed to protect low-pressure storage vessels from excessive positive pressure and vacuum. The family includes pressure-only, vacuum-only and combined pressure/vacuum arrangements for atmospheric discharge or connection to a closed vent line.

The valve uses weighted pallet and diaphragm assemblies that remain seated during normal operation and lift when tank pressure or vacuum reaches the selected set point. Opti-flow geometry is intended to provide high gas capacity from a compact valve body, while flanged atmospheric and piped-away configurations allow the vent path to match the plant layout. Material options include aluminium, carbon steel and stainless steel, with additional materials available for specific service requirements.

Current Motherwell data lists sizes from 2 to 12 in. (DN50–DN300) and pressure or vacuum settings from approximately 2 to 500 mbar depending on whether dead-weight or spring-loaded construction is selected. The range is available with ATEX and PED compliance where applicable, and Motherwell offers valve sizing to API 2000. Correct sizing must consider tank design pressure and vacuum, filling and emptying rates, thermal breathing, gas properties, piping losses and applicable standards.

A correctly selected breather valve protects the tank while limiting unnecessary vapour release, which can reduce product losses and help control emissions. Serviceable pallets, diaphragms, seals and optional proximity switches also support inspection and preventative maintenance over the valve lifecycle. AxFlow can support sizing, material and set-pressure selection, spare parts and service planning for Motherwell Opti-flow 380 installations.


Opti-flow 380 protects low-pressure storage tanks against excessive internal pressure and vacuum. It opens when the selected pressure or vacuum set point is reached and closes again as conditions normalise. Typical duties include bulk storage tanks, chemical tanks and related low-pressure systems.
Current Motherwell data lists valve sizes from 2 to 12 inches, corresponding approximately to DN50–DN300. The required size depends on the tank breathing load rather than only the nozzle diameter. AxFlow can support sizing against the actual filling, emptying and thermal breathing conditions.
Yes, the range includes configurations with pressure outlets and vacuum inlets connected to closed lines as well as atmospheric versions. This supports plants that need to route vapours into a recovery or treatment system. Backpressure and piping losses must be included in the sizing calculation.
Motherwell publishes settings from approximately 2 to 500 mbar across the dead-weight and spring-loaded range. The appropriate setting must remain within the allowable pressure and vacuum limits of the protected tank. The final configuration should be confirmed against the vessel design and applicable standards.
Selection should consider tank design limits, required venting capacity, set pressure, materials, vapour properties, connection size and discharge arrangement. Applicable ATEX, PED and tank-venting requirements should also be checked. Contact AxFlow for valve sizing, product selection and availability.
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