Pressure vacuum relief valve and its primary function

Pressure vacuum relief valve is designed to protect your tank from damage created by overpressure or excessive vacuum.

Pressure vacuum relief valve is designed to protect your tank from damage created by overpressure or excessive vacuum.

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

A Pressure Vacuum Relief Valve plays a fundamental role in controlling the pressure and vacuum levels in a storage tank, thereby preventing the catastrophic implications of a tank over-pressurization or vacuum collapse. Additionally, these valves prevent evaporation losses, minimise product contamination, and protect the environment from hazardous vapour emissions.

How does a pressure vacuum relief valve operate to maintain safe pressure levels and prevent damage to the system?

A Pressure Vacuum Relief Valve plays a fundamental role in controlling the pressure and vacuum levels in a storage tank, thereby preventing the catastrophic implications of a tank over-pressurization or vacuum collapse.

What are the main components of a pressure vacuum relief valve and their functions?

It’s essential to understand their components. These valves typically consist of elements such as the valve body, actuator, control element, and sensing mechanism.

• Breathing in: While the tank is being emptied, the PVRV breathes in to equalize the pressure inside and outside the tank, protecting it from a vacuum.
• Breathing out: When the tank is being filled, the PVRV allows air to escape to prevent excess pressure from causing the tank to swell.

How can pressure vacuum relief valves be tested to ensure they are working properly and within their specifications?

• Operate-in-place test: If the valve has never been tested before, lift the test lever. If the valve is stuck, remove the equipment from service until it can be repaired or replaced.
• Bench test: Shut down the facility’s system and remove all pressure relief valves. Then, transport the valves to a lab for testing and repairs.
• Set pressure test: After the set pressure test, perform a leak test by maintaining the test pressure at 90% of the set pressure. Then, count the number of bubbles produced per minute.
• Water heater test: Open the valve slightly with a bucket underneath to catch any dripping water. If you can see or hear water and gas escaping, the valve is working properly. Don’t force the valve open if you feel resistance.

What are the common failure modes of pressure vacuum relief valves and how can they be prevented?

• Contamination: Fluids can contain contaminants that can damage the valve’s internal components or sealing surfaces, or get lodged inside the valve. This can prevent the valve from closing, which can cause the system to lose pressure and functionality.
• Damage: Over time, the valve can become damaged or eroded by dirt and debris, preventing it from fully closing. This can cause the valve to chatter, which means it’s not fully open but is rapidly opening and closing.
• Leakage: Leakage can occur when debris or scale gets caught between the valve disc and seat’s sealing faces. It can also happen if the spring adjustment mechanism loosens during operation, causing the valve to continuously open.
• Wrong calibration: If the valve isn’t adjusted to the correct set pressure, it may cause early releases

To prevent failure, you can:

• Protect against contamination: Incorporate adequate protection against contamination upstream of the relief valve.
• Adjust the valve: Make sure the valve is adjusted to the correct set pressure. If the plant design changes, you may need to adjust the valve’s set pressure to align with the system’s new normal operating pressure.
• Inspect and maintain: Inspect and maintain the valve according to the manufacturer’s instructions.

What safety considerations should be taken into account when installing and operating pressure vacuum relief valves?

Lifting and carrying: If the valve has a handle or lever for manual operation, do not use it to lift or carry the valve. Testing: It is highly recommended to have a certified technician test a safety valve or pressure relief valve’s set pressure and seal tightness before installation.