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contraction occurs when the temperature of the product in the underground storage tank is higher than the BHOWLONG IS IT TAKING THE LEAK DETEC- temperature in the pipelines or dispensers. When the TOR TO PERFORM THE LINE TEST? product comes in contact with the pipeline, which is Per published information covering mechanical leak cooler, it contracts. this results in a decrease in volume detectors,the operation opening time when no leaks are (no loss of product occurs) and subsequently the line present is approximately two seconds. This time can pressure drops. vary, especially in systems with long piping runs, larger Thermal contraction may drop the pressure to zero diameter piping sizes and numerous flexible connectors. with only very minor changes in temperature (or even A time of up to 3-1/2 seconds should not be a cause for negative pressure(vacuum) if the difference in tempera- alarm. ture of product and line is great enough!) This is because This section discusses conditions that affect the the ambient temperature usually has a greater effect on length of time required forthe leak detectorto pressurize the pipeline,which is usually closer to the surface,than the line and open to the fuel flow condition. Thesefactors it does the product, which is normally stored in under- maybe permanent,orshort or longterm intermittent. The ground tanks, further below the surface. This simply effects of system size and construction are permanent. means that the leak detector will be making a line test Air may be present on a short term basis, such as when more frequently, and it becomes more critical to wait a filters are changed introducing air,or it may be trapped in few seconds after turning on the submersible pump high spots on a longterm basis. Vapor pockets as a result before opening the nozzle. of thermal contraction may form in lines between dis- This condition often occurs in the fall and early winter pensing on a short term basis, or overnight while the months and is more severe in locations where there is a station is shut down on a longer term basis. wide range of temperatures between day and night. This 1) Is longterm air resiliencypresentin the system? is usually true of mountain and desert areas where there are greater extremes in normal daytime highs and night- The leak detector cannot function properlywith air or other major resiliency present in the system. If there is air time lows. Summertime occurrences,although unusual, in the system, since it is lighter than the petroleum are possible when warm drops of product,such as those dproduct,it will accumulate at a high spot in the system. If directly delivered from refineries,are placed in a system. Tthe pressure goes to zero and the pump is turned on, The Piston LLD has a much larger reservoir than the approximately 3 gallons of product per hour will be diaphragm leak detector, and as a result will not go into metered into the discharge piping by the leak detector. the trip position as often as the result of thermal contrac- Since air is compressible,the product being metered into tion. The amount of reservoir present in the Piston LLD the piping will compress the air and the pressure will will keep it from being affected by thermal contraction in slowly rise until it is high enough for the leak detector to most installations. However, it may go into the trip move to its third or unrestricted f low position.The amount position in cases where there is an extreme case of of time that this takes is strictly dependent upon the thermal contraction. Conditions that affect the degree of amount of air in the system. Even a very small amount thermal contraction in a system other than temperature of air in the system can cause a prolonging of the time difference are piping size and length, the amount of required for the leak detector to complete a line test. product dispensed,andthetime interval beforethe pump is activated afterthe last dispensing. Slow station activity FIGURE 3 will allow a greater amount of thermal contraction. ® DISPENSER 4) Are there leaks downstream of the leak detector anywhere in the piping? Are there leaks In the dispenser? A minute weeping leak in one or more dispensers on the system can cause line pressure to drop to zero as well PRESSURE GAUGE as slowdown the operation of the leak detector. Remem- I ALL VALVE ber, any loss of pressure on product anywhere in the I ' system exposed to the leak detector, either upstream or r7 TUBING downstream, may affect the operation. Past experience CONTAINER OF has shown that,when testing leak detectors in a station, KNOWN VOLUME lt is im ortantto look inside dispensers for leaks that may FUSIBLE-LINK TEST PORT IN P P y SAFETY SHUT-OFF SAFETY VALVE not be caught by mechanical leak detectors because VALVE � o=°..•o ;; the are downstream of solenoid valves that are closed y FROM SUBMERSIBLE PUMP when the leak test is being performed. Fuel filters may also be leaking. It is important to check fuel filters with the , . Disable pump before Installing or pump running because they can develop a type of leak removing test equipment. Failure that does not discharge fluid until a higher pressure is to do so may result In accidental developed above the normal metering pressures of me- discharge of pressurized gasoline chanical leak detectors. The result is a discharge that which can cause severe personal may not be detected. Injury, death or substantial prop- erty damage If Ignored. -3-