Pressure-Vacuum Relief Valves, or P/V valves for short, are special venting devices designed to protect cargo and storage tanks from rupturing inwards (implosion) or outwards (explosion) due to pressure fluctuations under normal operating conditions. Factors that can cause a change in tank pressure include surrounding temperature and vapour quantity.
P/V valves allow for the flow of small volumes of air or gases into and out of the tanks when under-pressurised and over-pressurised respectively. This helps to keep tank pressures within their approved limits, preventing structural damage and marine pollution, serving as important safety devices for the operation of cargo and storage tanks.
However, despite their common main function, not all P/V valves are created equal. Here are some key things to consider when selecting the right P/V valves for your vessel.
What to look out for: P/V valves should be designed with upgradability and compliance longevity in mind. This comes in the form of easily accessible and installable original conversion kits or support from manufacturer for custom conversion solutions.
Why it’s important: Upgradability provides shipowners with the freedom to upgrade their P/V valve systems to meet new or different safety standards as necessary in the future. Upgrading of P/V valves can also allow ships to carry new categories of hazardous products, such as IIB cargoes. Upgradability ensures that the P/V valve system does not become obsolete after a few years of operation due to new safety regulations or the need to carry new categories of goods that the current system cannot comply with.
2. Low cargo emission
What to look out for: Operators should look out for P/V valves with high opening settings as they allow for higher tank pressures. Since higher pressure lowers the rate of evaporation, the rate of ventilation caused by over-pressurisation decreases as pressure builds up at a much slower rate. This consequently leads to lower cargo emissions.
P/V valves should also be equipped be resilient seals that are able to reseal the valves properly after each ventilation. This prevents leakage of cargo in the form of vapours escaping from the seal of valves when closed and lowers the demand for inert gas. Hence, low cargo emissions help to maximise profits and lower the cost of operation and is a key factor to consider.
Why it’s important: Well-designed P/V valves have low cargo emissions to reduce cargo loss during transit. Loss of cargo means loss in revenue and this amount can add up quickly over longer journeys.
3. Simplified construction
What to look out for: P/V valves should have simplified and service-friendly designs.
Why it’s important: This reduces the complexity and duration of maintenance works, allowing for maximum utility of vessels and lower maintenance costs as less time will be spent on repair and maintenance jobs. The reduction in number of parts also lowers the chance for mechanical failures, thereby reducing the cost of maintenance. In addition, certain manufacturers also offer maintenance kits to simplify the maintenance process.
4. Advanced flow control
What to look out for: The aerodynamic design and flow control of P/V valves is another important factor worth considering.
Why it’s important: P/V valves with better aerodynamic designs pose less obstructions to airflow, enabling higher exit velocities of gases even at low flow rates. This helps to create a safer working environment as toxic and flammable vapours are discharged vertically upwards, away from the vessel’s deck, at high velocities, thus reducing the risk of fire and explosion as well as the crew’s exposure to toxic vapours.
The simplicity of construction, upgradability of system, cargo emissions and control of airflow are all key things to consider when choosing your next P/V valve.
About GIANTECH: Established since 2001, GIANTECH is a Singapore-based marine engineering company with global operations in countries such as Croatia. The company specialises in the spare part sales and after-sales services for equipment such as inert gas systems, nitrogen generator systems, burners, boilers and P/V valves.
Visit http://www.igiantech.com to find out more.