The difference between a PRV and a PSV in Firefighting system

In a firefighting system (Oil & Gas) , a Pressure Relief Valve (PRV) and a Pressure Safety Valve (PSV) are both crucial safety components designed to manage pressure, but they have distinct purposes and operational characteristics.

1. Pressure Relief Valve (PRV):

• Purpose: A PRV is designed to release fluid (such as water, foam, or other extinguishing agents) from the system to prevent overpressure conditions that could cause equipment damage or system failure.
• Function: It opens proportionally to the increase in pressure. As pressure continues to rise, the PRV opens more to release the excess pressure gradually.
• Operation: PRVs can operate in a continuous or modulating manner, which means they may open just enough to relieve the excess pressure and then close when the pressure returns to safe levels. This allows for finer control of pressure fluctuations.
• Applications: PRVs are typically used in situations where controlled and gradual relief of pressure is needed to avoid shock or water hammer effects in the system. They are common in firefighting systems where maintaining system integrity is crucial.

2. Pressure Safety Valve (PSV):

• Purpose: A PSV is specifically designed as a safety device to protect equipment, personnel, and the environment from overpressure conditions. It is often considered the last line of defense.
• Function: The PSV is designed to open fully at a predetermined set pressure and relieve the maximum flow capacity until the pressure drops below the setpoint.
• Operation: PSVs operate in a "pop action" or "snap action" mode, meaning they open fully and rapidly when the set pressure is reached, and they do not close until the system pressure drops below a certain level, typically below the set pressure by a certain margin (blowdown).
• Applications: PSVs are used in critical applications where it is necessary to quickly relieve pressure to prevent catastrophic failure. In firefighting systems, they may be found in locations where sudden pressure buildup could pose significant risks, such as near pumps, tanks, or other critical equipment.

Pressure Relief Valve (PRV):

• Appearance: Typically, PRVs have a compact and cylindrical shape with a spring-loaded mechanism. They are often mounted horizontally or vertically.
• Features:A PRV will have an inlet and outlet port for the fluid to pass through.The body is usually made of metal (like stainless steel or brass) and can have flanged or threaded connections. You may notice an adjustment screw or knob on the outside, which is used to set the desired pressure limit.The internal mechanism consists of a spring and a seat that modulates the opening, allowing for gradual release of fluid.

Pressure Safety Valve (PSV):

• Appearance: PSVs are generally larger and more robust than PRVs, with a noticeable bell or dome-shaped housing that contains the spring mechanism.
• Features:The PSV will have a similar inlet and outlet configuration, but it is built to handle higher pressure and capacity. It usually has a pop-off design, with a spring-loaded mechanism that allows it to open fully when the set pressure is reached.There might be a lever or pull ring on the valve body for manual testing or activation.The body is typically made from high-strength metals and may have additional features like a pressure adjustment lever and a cap to protect the internal mechanism.

For a General Arrangement Drawing (GAD) layout of the Pressure Relief Valve (PRV) and Pressure Safety Valve (PSV), I'll describe what these layouts typically include:

1. General Arrangement Drawing (GAD) for Pressure Relief Valve (PRV):

• Front View: 1) The drawing will show a vertical section of the PRV with key dimensions (height, width, and flange diameter) 2) Details like the spring mechanism, adjustment screw, and inlet/outlet connections 3) Material specification for each component (e.g., body, seat, spring).
• Side View: 1) This view will depict the valve's profile, showing the flow direction and internal components' positions 2) Connection details, such as the type of flange or thread, size, and rating.
• Top View: 1) A view from above to illustrate the valve's outer dimensions and connection points 2) Position of the adjustment screw or knob and any other external accessories.

2. General Arrangement Drawing (GAD) for Pressure Safety Valve (PSV):

• Front View: 1) A vertical section showing the PSV's body, spring housing, and lever or pull ring 2) Key dimensions such as height, width, inlet/outlet size, and the size of the dome housing 3) Material details for the body, seat, spring, and other parts.
• Side View: 1) Shows the valve's profile, highlighting the pop-off design, lever, and mechanism to allow for rapid release 2) Flow direction indicated with arrows and any manual test features.
• Top View: 1) Illustrates the valve's overall size and flange connections 2) Position of the lever or pull ring and any external features.

Here's a breakdown of their key components and how they function in the firefighting system:

Components of a Pressure Relief Valve (PRV):

1. Body: The main housing of the valve, typically made from materials like stainless steel, brass, or other corrosion-resistant metals, depending on the fluid and pressure requirements.
2. Inlet and Outlet Connections: Flanged or threaded connections that allow the valve to be installed in the pipeline. These connections are designed to handle the flow of water, foam, or extinguishing agents.
3. Spring Mechanism: A calibrated spring that controls the valve's opening and closing. The spring's tension is set to open the valve gradually when the pressure exceeds a specific setpoint.
4. Disc or Poppet: A movable component that seals the valve when closed and lifts when the pressure exceeds the setpoint, allowing the fluid to escape.
5. Seat: The area where the disc or poppet rests to create a seal. It ensures a tight closure to prevent leakage under normal operating conditions.
6. Adjustment Screw/Knob: A feature that allows for the adjustment of the spring tension, thus setting the desired pressure at which the valve will open.
7. Bonnet: The part of the valve that covers and protects the spring mechanism. It may be removable to allow for maintenance or adjustment.
8. Flow Passage: Internal pathways that direct the fluid through the valve when it opens to relieve pressure.

Components of a Pressure Safety Valve (PSV):

1. Valve Body: A robust housing made of high-strength materials (like carbon steel or stainless steel) to withstand high pressure and harsh environmental conditions. The body typically includes a dome or bell-shaped top.
2. Inlet and Outlet Connections: Flanged connections designed to handle high pressure and allow the valve to be securely connected to the system piping.
3. Spring Assembly: A heavy-duty spring that is designed to "pop open" rapidly when the set pressure is reached, allowing a full release of pressure. The spring is calibrated for a specific pressure setpoint.
4. Disc or Valve Seat: A component that provides a tight seal under normal operating conditions and lifts rapidly to open fully when the pressure exceeds the setpoint.
5. Blowdown Ring: An adjustable ring that allows fine-tuning of the valve's blowdown (the pressure differential between opening and reseating), ensuring the valve closes properly after the overpressure event.
6. Bonnet or Dome Housing: The upper part of the valve that houses the spring and lever mechanism. It provides space for the spring's expansion and contraction.
7. Lever or Pull Ring: A manual device used to test or activate the valve manually. It is especially useful during maintenance checks or for emergency situations where a rapid release is necessary.
8. Nozzle: The opening through which the fluid is discharged when the valve opens. The nozzle is designed to handle high flow rates and direct the discharge safely away from equipment and personnel.
9. Pressure Setpoint Indicator: A marking or device that indicates the pressure at which the valve is set to open. This helps ensure the valve is set correctly for the system’s requirements.

How They Function in a Firefighting System:

• PRV (Pressure Relief Valve):
• Role: In a firefighting system, the PRV helps maintain the correct operating pressure in the pipeline network or at specific equipment (like pumps).
• Operation: If the pressure rises above the setpoint, the PRV opens gradually to release excess pressure, preventing overpressure situations that could damage components like hoses, pumps, or nozzles.
• Application: Installed near pumps, along pipelines, or at points where pressure buildup could occur due to the firefighting water or foam network.

• PSV (Pressure Safety Valve):
• Role: Serves as an emergency safety device to prevent catastrophic overpressure events that could lead to equipment failure, fire, or explosions.
• Operation: The PSV is set to a specific maximum pressure; when this pressure is reached, the valve pops open completely, rapidly releasing pressure to protect the system.
• Application: Typically installed at critical points where sudden pressure surges might occur, such as at pump discharge points, storage tanks, or high-risk areas of the firefighting system.

deeper into the specific components of the Pressure Relief Valve (PRV) and Pressure Safety Valve (PSV) and explain their roles in a firefighting system.

Detailed Components of a Pressure Relief Valve (PRV):

1. Valve Body: Description: The main structure or casing of the PRV, typically made from materials like stainless steel, brass, or other corrosion-resistant metals. It houses all internal components. Role: Provides structural integrity to withstand system pressures and protects internal components from external damage. In a firefighting system, the body must be resistant to corrosion, high pressure, and potential impacts.
2. Inlet and Outlet Connections: Description: The points where the valve connects to the firefighting pipeline. These connections can be flanged, threaded, or welded, depending on the system's design. Role: Allow the PRV to be integrated into the firefighting network, ensuring the valve can relieve pressure effectively by releasing excess fluid when needed.
3. Spring Mechanism: Description: A calibrated spring inside the valve that determines the pressure at which the valve opens. The tension of the spring is set to a specific setpoint pressure. Role: Controls the valve’s opening and closing actions. When the system pressure exceeds the setpoint, the spring compresses, allowing the valve to open and gradually relieve excess pressure. In firefighting systems, this prevents damage to pipes and equipment due to overpressure.
4. Disc or Poppet: Description: A movable component inside the valve that seals against the seat to prevent fluid from escaping when the valve is closed. Role: Acts as the closure element of the valve. When the pressure exceeds the setpoint, the disc lifts away from the seat, allowing the fluid to pass through and relieve pressure.
5. Seat: Description: The area where the disc or poppet rests when the valve is closed. Role: Provides a leak-tight seal under normal operating conditions. Ensures that there is no leakage when the pressure is within safe limits.
6. Adjustment Screw/Knob: Description: An external component that allows adjustment of the spring tension. Role: Used to set or adjust the pressure at which the valve will open. This is important in a firefighting system to calibrate the PRV according to specific system requirements.
7. Bonnet: Description: The part of the valve that covers the spring mechanism. Role: Protects the internal components of the valve from dirt, debris, and environmental elements, ensuring the PRV operates reliably over time.
8. Flow Passage: Description: Internal channels that direct fluid flow through the valve. Role: Ensure smooth and controlled fluid flow when pressure is relieved, preventing shock waves or "water hammer" in the firefighting system.

Detailed Components of a Pressure Safety Valve (PSV):

1. Valve Body: Description: The main casing of the PSV, typically larger and more robust than a PRV to handle higher pressures and rapid releases. Role: Designed to withstand sudden and significant pressure surges. It provides a secure housing for all internal components and is built to protect against catastrophic failures in firefighting systems.
2. Inlet and Outlet Connections: Description: Flanged connections designed for high-pressure applications, often reinforced to handle full bore discharge. Role: Connect the valve securely to the firefighting pipeline, allowing for the rapid release of fluid when the valve activates.
3. Spring Assembly: Description: A heavy-duty spring calibrated to open the valve rapidly when the pressure exceeds a setpoint. Role: Triggers the "pop-open" action of the PSV. When the pressure reaches the preset level, the spring compresses quickly, allowing the valve to open fully and discharge fluid rapidly to prevent overpressure.
4. Disc or Valve Seat: Description: A movable closure component that seals against the valve seat under normal conditions. Role: When overpressure occurs, the disc lifts quickly from the seat to allow the maximum flow of fluid through the valve. This design ensures a rapid response to prevent dangerous pressure buildup.
5. Blowdown Ring: Description: An adjustable ring within the valve body. Role: Allows fine-tuning of the blowdown, which is the difference between the opening pressure and the pressure at which the valve reseats after activation. This helps ensure that the valve closes correctly after the pressure has been relieved.
6. Bonnet or Dome Housing: Description: A dome-shaped housing at the top of the valve that contains the spring and lever mechanism. Role: Provides space for the spring to expand and compress. It also serves to protect the spring mechanism from environmental damage.
7. Lever or Pull Ring: Description: A manual device attached to the valve. Role: Allows operators to manually test or activate the valve. In firefighting systems, it is used for periodic testing to ensure the valve's readiness or in emergencies to manually relieve pressure.
8. Nozzle: Description: The opening through which fluid is discharged when the valve is activated. Role: Designed to handle high flow rates and direct the discharge safely away from equipment and personnel, preventing damage or injury in high-pressure scenarios.
9. Pressure Setpoint Indicator: Description: A marking or device on the valve that indicates the set pressure at which it will open. Role: Ensures the valve is set correctly for the system’s specific safety requirements, allowing maintenance personnel to verify the valve settings.

Their Roles in a Firefighting System:

• PRVs are used to protect equipment by gradually relieving pressure in the firefighting network, ensuring the system operates within safe pressure limits.
• PSVs are critical safety devices designed for emergency use, providing rapid and full release of pressure to prevent catastrophic failure due to overpressure events.

These components together ensure that the firefighting system remains reliable, effective, and safe, particularly in the high-risk environment of an oil and gas field.