PV-VOC: The Crude Oil Tanker P/V Valve

The PV-VOC is designed to meet the requirements that larger Crude Oil Carriers have for P/V valves.

The PV-VOC is designed to reduce the amount of cargo vapor, by implementing a special 2-step opening sequence. 

Main functions and features


  • The PV-VOC valve is designed, tested and manufactured to provide maximum safety for crew, cargo and vessel.
  • The pressure unit has been designed to ensure that the efflux velocity is always above the required minimum of 30 m/s and typically between 60-100 m/s.
  • The cone of the pressure unit has been optimized to secure vertical vapour dispersing, which combined with the high efflux velocity ensures, that gas is safely led away from the deck.
  • The PV-VOC valve has been extensively fire tested at the world’s leading test laboratory in Tests include endurance burn testing and flash-back testing in accordance with all relevant rules.
  • The resilient seal provides protection against leakage and reduces emissions to virtually zero. 

Pres-Vac is ISO 9001 certified to ensure consistency of the high-quality products that Pres-Vac is known for.

Compliance with rules and regulations

  • The PV-VOC valve is designed, tested and manufactured to be in compliance with all existing and foreseen international regulations.
  • In 2013 the European Commission adopted EN ISO 16852:2010 as a new standard for testing of flame arrestors to be installed onboard marine vessels. As the first P/V valve on the market, The PV-VOC valve has been designed, tested and approved to comply with this new standard. 
  • Flashback testing at low flow rates in accordance with EN ISO 16852:2010. The flashback tests shall be performed on pipe lengths equal to or longer than the pipe length, on which the valves are to be installed. This is mandatory according to EN ISO 16852:2010.


The patented PV-VOC pressure/vacuum valve is designed to optimize the VOC performance. Using fluid dynamic simulation software in connection with testing, we have achieved a performance that benefits all stages in the operation of an oil tanker. This includes filling, topping, breathing or VOC savings in accordance with the VOC management procedure required by IMO/MSC/ Circ.680.

Performance in four phases: 

  1. The breathing phase

When the vessel is in the voyage and the only influences on the pressure in the cargo tank are the thermal variation and the movements of the ships, the valve will be in the breathing phase.

The breather performance will ensure that the pressure is kept on top of the cargo avoiding any unnecessary emission of VOC. The valve performance is characterised by the ability to open and close at the same pressure level. This performance is kept until approximately 50% of the total flow capacity is reached. Then the valve will enter the fully open phase.

2. The fully open phase

The valve will enter the fully open phase when the vessel is loading and the full flow capacity is required. The pressure unit will open up fully and ensure, that the pressure is maintained at the opening setting level. The design of the valve ensures a steady, non-oscillating behaviour keeping a constant pressure in the venting system until the loading has finished. The valve will then enter the closing phase.

3. The closing phase

When the cargo tank is getting close to full, the loading rate will decrease and the valve will enter the closing phase. The valve will start closing, still keeping a sufficient pressure on the cargo. The closing phase will be performed while ensuring that the blowdown will be as small as possible. The valve will still be open in this phase, but the performance will stop the evaporation of the cargo.


4. Topping off phase

When the cargo tank is almost full (closing towards 98%) the topping of the tank will result in a significant decrease in the loading rate to avoid the cargo from creating a sudden overpressure. This will force the valve into the final closing phase. In this phase, the valve will close at the same pressure as it opened, thus preserving the VOC in the cargo tank in compliance with the IMO/MSC/Circ. 680.

Effective relief of tank pressure

The PV-VOC valve provides effective control and management of the tank pressure. If the pressure exceeds the specified opening setting, the valve will open immediately and relieve the excess pressure. Similarly, if pressure during discharging gets below the specified opening pressure, the valve will open and relieve the vacuum.

The PV-VOC valve has an advanced flow control design to manage tank pressure:

  • The tank pressure valve is controlled by a combination of magnet and weight forces to secure that the valve does not create a pressure surge during the opening. 
  • A patented combination of a booster plate and pressure control ring secures that the valve has a soft opening and closing phase ensuring efficient operations also at low flow. 

Configured to your requirement

Pres-Vac P/V valves are individually configured to suit your specific requirements:

  • 5 different sizes of pressure units combined with 5 different sizes of vacuum units
  • Variable flange sizes
  • All flange standards available and any customized version
  • Options include integrated gas freeing cover, coating, heating, low-pressure setting
  • Two different product versions

Low noise level

The PV-VOC valve is designed to minimise noise during operations. By optimising the nozzle design, the noise level of the PV-VOC valve has been reduced by 10-15 dB compared to other designs. In many applications, hearing protection will not be required.


Operations and maintenance made simple

The PV-VOC valve has been designed to simplify operation and maintenance. Daily operations

by the crew are made simple by the following features:

  • New two-way operating full stroke check lift
  • Visual inspection of all moving parts
  • Dirt indicator/cleaning port
  • Hinged type gas freeing cover

Additional features

The PV-VOC valve has been made easier to maintain as follows:

  • The number of parts has been reduced by 30% and the valve is very simple to disassemble and maintain.
  • The weight of the valve has been significantly reduced.
  • Check lift can be maintained without disassembly of
  • Easy calibration of setting after
  • Regular maintenance can easily be performed by on-board
  • Replaceable vacuum flame arrestor, gas freeing flame screens and integrated resilient seal. 


Specific requirements

The PV-VOC valve is always configured to meet the specific requirement of every single customer.

Different vessel designs need different venting requirements for pressure and vacuum valves. Furthermore, vessel designs tend to use different piping arrangement and consequently require different flange sizes and flange standards.

The pressure and vacuum unit of the valve can be delivered in five different sizes. The pressure and vacuum units can be freely combined to deliver the combination most suitable for your vessel.

All the combinations can be delivered in different flange sizes and with all flange standards.

Furthermore, Pres-Vac offers a broad range of options for the PV-VOC valve:

  • integrated gas freeing cover
  • heated versions
  • low and high-pressure setting
  • custom coating

Custom solutions and special requirements can be delivered upon request.

Option: Integrated gas freeing cover

The gas freeing cover is installed as an integrated version on top of the vacuum valve. It can easily be operated without using tools.

The design ensures that the cover releases the maximum amount of vapour that the size of the piping allows.

Option: electric, steam or thermal Heating

The pressure unit and the vacuum unit can be equipped with a heating device. This prevents ice accretion*, which will result in malfunction. The heating will also prevent certain cargoes with a

high pour point from crystallising, as the temperature can be kept at a suitable level.

* Ice Accretion occurs when waves or heavy rain is present with surface temperatures at or below freezing. A layer of ice will accumulate and prevent the valve from functioning properly.

Option: Custom coating

As a standard the PV-VOC valve is delivered with the following Hempel paint:

  • 2 x HEMPADUR 45141 (2 x 100 mic thickness)
  • 1x HEMPATHANE 55210

(1 x 50 mic thickness) Red 5063 outer colour.

However, it is possible to deliver the PV-VOC valve in any colour.

The ultimate


You should choose a PV-VOC Ultimate if you are particularly concerned about leakage protection, loss of inert gas, disc/seat and flame screen maintenance costs.

The PV-VOC Ultimate delivers all the features of the PV-VOC Superior and three additional safety and maintenance features:

  • Seat with integrated resilient
    • The integrated resilient seal provides ultimate leakage protection and also reduces wearing of disc and seat.
  • Flame screens in AISI 316 L stainless
    • To reduce wear from high corrosive cargoes and to extend maintenance intervals, flame screens are delivered in AISI 316 L stainless steel.


You should choose the PV-ECO Superior if your focus is to get a safe and very reliable P/V valve of high quality.

Main features:

  • Optimal safety
  • Compliance with all current rules and regulations Low noise
  • Low blowdown
  • Simple operations and maintenance

Resilient seal

  • Elimination of leakage
  • Reduction of wear and tear
  • Easy replacement
  • Made of an advanced, non-flammable

Suitable for chemical and oil products.


Maximum safety for crew, vessel and cargo

  • High vertical gas dispersion
  • Low noise
  • Extensively tested by an independent test laboratory
  • Integrated leakage protection (Ultimate version)

Compliance with all current and foreseen regulations

  • No risk of non-compliance
  • Complies with the latest European standard for fire testing

Designed to your needs

The valves can be optimized to effectively meet your venting requirements.

Excellent operational performance

  • The combination of weight and magnetic force protects against pressure surges and secures high closing
  • Leakage protection ensures maximum safety, minimises loss of inert gas and cargo

Low maintenance costs

  • The modular design of the valve makes the replacement of wear parts and spare parts
  • Lifetime availability of spare parts and a global network of service

Emission Reduction

  • Breather functionality


  • Pres-Vac Engineering A/S
    Solvang 22
    3450 Allerød