The EPA has new performance standards, and government agencies have engaged in the enforcement of those requirements with the use of newly sophisticated equipment that will challenge manufacturers of conservation and emergency vents to improve their designs. Many states have started targeting high-emission areas with aerial equipment that uses thermal imaging technology to find systems clearly operating outside the rules. Also, tank owners have started their own inspections to minimize product losses to the environment and increase profits.
Vent requirements
In order to pass emission tests, high-quality pressure and vacuum vents with tight shutoffs are necessary to meet new performance requirements. These vents normally state they have less than 1 standard cubic foot per hour (SCFH) of seat leakage at 90 percent of the specified set point. My recommendation is for vents always to be 100-percent tested to meet requirements and also delivered with calibration and test certificates as standard procedure. Tested vents help establish a solid baseline performance for installers/ maintenance personnel to set up periodic inspection schedules.
Controlling vapors
With many of the tanks in service being built to API 12D and 12F standards, the pressure limits of the tank become a concern when choosing the setting of the pressure/vacuum vents. It can be difficult to contain vapors inside a tank and maximize efficiency if the pressure is not allowed to rise or fall to the individual tank design limits. Choosing those settings is a calculated approach recommended for vent manufactures who have actually tested their product per API 2000 setups and sized the vents using API 2000 methods appropriately. Vent sizing should be performed on all vents from weight-loaded to pilot-operated vents. The most common vent is weight-loaded for price and simplicity, and it suits the job well if designed to meet the minimum required seat leakage previously mentioned. However, pilot-operated technology on tank vents has raised the bar by ensuring bubble-tight shutoffs while safely approaching the design pressures of the tanks with snap-action settings.
The high-end equipment
Good pilot-operated vent performance is fundamentally improved over weight-loaded units due to the imbalance of actuator area to pallet seat area. Designed pressure imbalances result in units on the market that actually seal tighter and perform better as tank pressure rises. The vast combinations of actuators, pallet designs, material compositions of diaphragms, pilot setup and sensing options can produce near bubble-tight seat leakage in many circumstances at varied percentages of pressure set point. Commonly, the blowdown needle adjustment can ensure the return of bubble-tight shutoff after fully opening at better than 90 percent of the set point. In general, 10-percent overpressure is the respected design by manufacturers. It is possible to achieve less than 2-percent overpressure if needed before the vents are flowing at maximum potential. Pilot-operated technology thought to be over-the-top for common tank setups is the expected new frontrunner in an industry operating inside federal rules and regulations.
For more information on the National Institute for Storage Tank Management, visit www.nistm.com or call (800) 827-3515. For more information on this topic, email sales@cashco.Com, call (785) 472-4461 or visit www.Cashco.com.
