| Choose | Define the protected equipment | Tank type, design pressure, design vacuum, operating temperature, fluid, vapor space, and allowable nozzle loads | Select a valve specifically rated for the tank's pressure and vacuum service. A tank vent valve is not automatically suitable for a pressure vessel or process line. | Design pressure and vacuum limits are documented and are not exceeded by the proposed valve settings. | Approved equipment datasheet and design-basis document |
| Choose | Identify the required protection mode | Normal filling, emptying, thermal breathing, emergency heating, fire exposure, inert-gas blanketing, and upset conditions | Use pressure relief, vacuum relief, or a combined pressure-vacuum vent as required. Emergency venting may require a separate device or an engineered emergency vent system. | Every credible overpressure and vacuum scenario has a documented protection method. | Relief scenario review and cause-and-effect matrix |
| Choose | Set pressure and vacuum limits | Tank design pressure, design vacuum, operating pressure range, and required margin between operating and set conditions | Set pressure below the protected tank's maximum allowable pressure and set vacuum above the tank's maximum allowable vacuum. Do not select settings from a generic table without confirming the tank design data. | The pressure and vacuum settings remain within the tank manufacturer's or engineer's approved limits. | Signed setting calculation and valve set-point certificate |
| Choose | Calculate required capacity | Maximum liquid filling rate, maximum withdrawal rate, gas flow, vapor generation, thermal expansion, emergency heat input, and relieving conditions | Size the valve for the governing pressure-relief and vacuum-relief cases. Convert all flow values to consistent mass or standard volumetric units before comparing capacity. | Rated capacity is equal to or greater than the calculated required flow at the specified relieving conditions. | Capacity calculation with assumptions and input sources |
| Choose | Select valve construction | Fluid compatibility, corrosivity, solids, polymerizing tendency, temperature, humidity, and outdoor exposure | Confirm body, seat, disc, spring, gasket, and screen materials. Consider corrosion-resistant materials and a weather hood where environmental exposure could affect operation. | All wetted and exposed materials are compatible with the stored product and site environment. | Material compatibility review and service specification |
| Choose | Check connection and flow-path requirements | Nominal connection size, flange or threaded connection, inlet losses, outlet backpressure, piping length, and discharge direction | Use a short, adequately sized inlet connection. Avoid restrictions, long narrow piping, liquid traps, and discharge arrangements that can obstruct or freeze. | Connection dimensions match the approved drawing; calculated pressure loss does not prevent the valve from reaching required capacity. | General arrangement drawing and piping review |
| Install | Verify the valve before installation | Model, size, pressure and vacuum settings, flow direction, test certificate, damage, contamination, and protective caps | Inspect the device after transport. Keep protective packaging in place until installation, but remove all shipping restraints, plugs, and temporary covers before commissioning. | Valve identification and settings match the approved purchase and engineering documents. | Receiving inspection checklist and photographs |
| Install | Prepare the tank nozzle and piping | Nozzle cleanliness, flange alignment, gasket type, bolt condition, support, drain arrangement, and internal obstructions | Clean the connection, align piping without forcing the valve, use the specified gasket, and provide independent support where piping weight could load the valve body. | No foreign material enters the tank; the valve is not used to correct pipe misalignment. | Installation inspection and torque record |
| Install | Orient and connect the valve | Manufacturer-approved orientation, atmospheric discharge path, weather protection, and hazardous-area requirements | Install in the orientation required by the design. Keep the vent path open and route hazardous vapors to a safe location when required by the risk assessment and local regulations. | Discharge is unobstructed, safe for personnel, and protected from rain, insects, snow, dust, and ice where applicable. | As-built drawing and field verification form |
| Install | Control contamination and leakage | Pipe cleanliness, flushing method, sealant location, gasket compression, and leak-test medium | Prevent thread sealant, gasket fragments, welding debris, and paint from entering the valve. Do not apply sealant where it can migrate into the operating mechanism. | No visible leakage or obstruction is present after installation and pressure stabilization. | Cleaning certificate and leak-test report |
| Test | Perform a pre-start functional inspection | Valve freedom of movement, vent opening, lifting device condition, flame or weather screen condition, and isolation-valve status | Confirm that isolation valves are locked or car-sealed in the required operating position. Never commission a tank with its only relief path inadvertently isolated. | Relief path is available, correctly aligned, and free from temporary covers or blockages. | Pre-startup safety review checklist |
| Test | Verify pressure and vacuum set points | Calibrated pressure or vacuum source, test medium, test temperature, test procedure, and allowable tolerance | Test pressure and vacuum functions separately when the device provides both. Use a calibrated reference instrument with a suitable range and accuracy for the set points. | Opening or lifting occurs within the approved tolerance stated by the applicable specification or site procedure. | Calibration certificate, test chart, and set-point result |
| Test | Check reseating and leakage | Reseating pressure or vacuum, seat leakage method, stabilization time, and test temperature | After opening, confirm that the valve reseats without sticking, chattering, or continuous leakage. Apply the specified leakage acceptance method for the valve type. | Valve reseats consistently and leakage is within the approved test limit. | Functional test report and leakage result |
| Test | Confirm alarm and monitoring interfaces | Position switch, pressure transmitter, tank pressure indicator, remote alarm, and control-system logic | Where installed, simulate the alarm or switch condition and verify the signal at the receiving system. A monitoring signal does not replace the mechanical relief function. | Correct alarm, tag number, status, and operator indication are confirmed. | Loop-check sheet and alarm test record |
| Maintain | Conduct routine visual inspections | Inspection frequency, product service, weather severity, dust, corrosion, icing, deposits, and unauthorized changes | Inspect at a risk-based interval. Look for blocked openings, damaged screens, corrosion, loose fasteners, product deposits, leakage, and signs of lifting. | Vent opening and discharge path remain clean, open, and physically undamaged. | Inspection log with date, condition, and corrective action |
| Maintain | Clean the valve and vent path | Product residue, dust, insects, crystallization, polymer deposits, ice, and cleaning compatibility | Clean using a procedure compatible with the valve materials and stored product. Do not use tools or solvents that can damage seats, diaphragms, coatings, or screens. | Moving parts operate freely and cleaning has not changed the approved setting. | Cleaning record and post-cleaning functional check |
| Maintain | Inspect internal components | Seat condition, disc alignment, spring condition, guides, gaskets, hinge points, and corrosion | Disassemble only under an approved procedure by qualified personnel. Replace damaged or degraded parts with components specified for the service. | No sticking, galling, excessive wear, deformation, or loss of spring integrity is found. | Maintenance work order and component inspection report |
| Maintain | Recalibrate and retest | Service criticality, valve history, previous test results, failure history, operating severity, and regulatory requirements | Establish the interval through a documented risk-based program and applicable regulations. Retest after repair, setting adjustment, severe corrosion, abnormal lifting, or a significant process change. | The current test date, next due date, settings, and results are traceable to the valve identification. | Calibration certificate and maintenance history |
| Maintain | Manage change and spare parts | Tank service changes, new product, changed filling rate, changed blanketing pressure, replacement parts, and revised regulations | Recalculate capacity and settings whenever operating conditions or tank design assumptions change. Store clean spare parts in sealed packaging and protect soft goods from heat and sunlight. | Any change is reviewed and approved before the valve returns to service. | Management-of-change record and spare-parts register |
