The Groth Emergency Relief Valve (ERV) is a critical safety device designed to protect liquid storage tanks and other process vessels from structural damage due to excessive internal pressure or vacuum. These emergency situations can arise from fire exposure, failure of inert gas blanketing systems, or changes in temperature and pumping rates. The ERV provides emergency relief capacity beyond that offered by normal operating pressure relief valves.
Function Description:
The primary function of the ERV is to act as a self-closing valve that relieves pressure or vacuum when it exceeds specified limits and then reseats once the overpressure or vacuum has dissipated. This mechanism prevents tank rupture or collapse, which could lead to severe personal injury, death, and material damage.
Storage tanks experience pressure increases when liquid is pumped in, compressing existing vapor, or when rising temperatures cause increased evaporation or expansion of vapor. Conversely, vacuum conditions can occur during liquid pump-out or decreasing temperatures. The ERV ensures that vapor can escape or enter the tank at a controlled rate, determined by factors such as tank size, content volatility, pumping rate, and temperature, in accordance with API Standard 2000.
The Groth 2000A Series offers four models:
- Model 2000A: Provides pressure relief only with a guided cover. Vacuum relief must be supplied by a separate breather valve.
- Model 2050A: Offers both pressure and vacuum relief through a spring-loaded port integrated into the cover assembly, featuring a guided cover with a weatherhood and screen for protection.
- Model 2400A: Provides pressure relief with a hinged cover, which improves alignment for proper reseating after venting.
- Model 2450A: Combines the hinged cover design with vacuum relief capability.
All models allow their covers to be lifted off the base for quick access during tank inspection and maintenance. Depending on the pressure setting, a crane or other lifting device may be necessary to open or remove the cover assembly. Some models also include a restraining cable that connects the head and flanges, doubling as a grounding cable to prevent static electric discharge.
Important Technical Specifications:
- Set Pressure and Set Vacuum: ERVs are factory-preset according to purchase order specifications, with nominal flow capacity stamped on the valve nameplate. Readjusting these settings or adding weights to the pallet assembly without consulting the factory is strictly prohibited, as it can alter relief settings and potentially lead to tank failure.
- Rated Capacity: Emergency relief valves are designed to provide full rated capacity at 100% over-pressure. If operation at a reduced over-pressure is required, the factory must be consulted for actual flow capacity under specified conditions.
- Pallet Assemblies: Pallet assemblies are heavy, potentially exceeding 400 lbs, requiring external lifting methods to prevent bodily injury. Mixing pallet assemblies from different valves is forbidden, as it can change relief settings and cause tank failure.
- Seating: The valves feature Groth's "cushioned air" seating. FEP seating diaphragms are standard, designed to minimize sticking from resinous vapors and atmospheric moisture. Diaphragms are also available in Buna-N, FKM, and other elastomers. Peripheral guides ensure proper alignment and seating integrity.
- Flange Compatibility: Standard bodies are furnished with flat flanges and should be mounted on a flat-faced 150# ANSI or API 650 flange. A full-faced gasket is recommended to prevent body flange deflection. Connecting flanges must be flat within 0.015" and free of scratches, corrosion, and tool marks.
- Grounding: The ERV is equipped with a ground strap to prevent static electric discharge. This strap must be properly secured to a ground point, allowing valve operation, to prevent tank rupture and severe injury or death.
Usage Features:
- Emergency Protection: Provides crucial protection against overpressure and vacuum conditions in storage tanks and process vessels.
- Self-Closing Design: Automatically reseats after relieving pressure or vacuum, ensuring continuous protection.
- Accessibility for Maintenance: Covers can be lifted for easy inspection and maintenance.
- Model Versatility: Offers models with pressure-only relief, or combined pressure and vacuum relief, with guided or hinged covers to suit different application requirements.
- Factory Preset: Valves are preset at the factory, simplifying initial deployment, with settings clearly marked on the name tag.
Maintenance Features:
- Periodic Inspection: Valves should be checked periodically, at least twice a year, to confirm proper functioning.
- Soft Goods Kits: Soft goods kits, including diaphragms and washers, are available for replacement. A specific numbering system (e.g., KS200016T) is used for ordering kits based on model, size, and soft good material (Aflas, Buna-N, FFKM, Fluoropolymer, FKM).
- Seat Maintenance: The body seat area must be free of corrosion, damage, or product build-up. If damaged, the seat must be lapped using a perfectly flat ground metal disc and fine grit emery cloth. Soft goods should typically be replaced during valve maintenance.
- Cleanliness: Components must be clean and have smooth contact surfaces to maintain a tight seal.
- Disassembly and Assembly Procedures: Detailed instructions are provided for disassembling and reassembling each model, including specific steps for handling components like weight plates, diaphragms, and springs.
- Testing Procedures: Comprehensive testing procedures are outlined for verifying set pressure, set vacuum, and seat tightness using a tank vent test stand or blind flange with an instrument tap. This includes slowly increasing pressure/flow and recording seat leakage and set pressure.
- Troubleshooting: Guidelines are provided for addressing excessive leakage, including inspecting the seat, diaphragm, pallet flatness, and verifying assembly weight.
- Safety Precautions: Emphasizes critical safety warnings, such as releasing all pressure before removing the valve, observing plant procedures and Material Safety Data Sheets (MSDS) when handling process vapors, and using appropriate personal protective equipment (eye protection, respiration, skin contact).
- Ground Cable Replacement: When replacing the ground cable, surface corrosion must be thoroughly cleaned to ensure proper grounding between the pallet and tank nozzle.
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