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PISTON LEAK DL._CTOR stream from . If, two or three dispensers on the same product rade with very small, weeping joints can be P 9 rY P� 9 enough to make the leak detector take considerably longer than normal to open. i IS ENOUGH TIME ALLOWED FOR THE LEAK TEST? (I.E. IS THE SYSTEM STAYING CLOSED METERING PISTON L ONG ENOUGH FOR THE TEST TO BE COMPLETED?) SEAL 1) Time delays History has taught us that one cannot rely upon the nozzles being closed long enough priorto dispensing,for the leak detector to complete its test. As a result, some �\ dispensing equipment provides a delay in the opening of the solenoid valve after activation of the pump or a delay FIGURE 4Bp \ \� in allowing flow to the nozzle after activation of the um and solenoid valve. This characteristic may be an simulated leak in place and allow the leak detector to integral part of the design or accomplished by retrofit. meter for about ten (10) minutes. The theory in these cases, is that flow is not allowed Leaking product through to vent to the hose until completion of the three-step leak test is tubing must be caught in a suitable accomplished. In other words, the system remains container to avoid accidental dis- sealed until the leak detectorcancomplete the three-step charge of product. This can cause leak test. However, if a leak at the rate of approximately severe personal injury, death or 3 gph or greater is present in the system,downstream of substantial property damage if ig- the leak detector, the line pressure cannot increase nored. adequately to allow the poppet to go from the metering If the metering seal is bad,fluid will flowthrough the leaky position to the full flow position, regardless of the delay seal, through the piston relief valve and out of the vent allowed. Even with a built-in delay, if the test time is tube while the leak detector is in the metering position. longer than the delay allows for, the result may be Line pressure should be 15 - 22 PSI during this time. restricted flow by the leak detector. To check if sufficient time is available for the leak 5) Is thermal contraction slowing down the leak detector to perform its test, a pressure gauge should be detector? installed as in Figure 3. (Observe warning on Fig. 3). Thermal contraction occurring while the leak detec- The gauge is part of the leak detection test apparatus. for is performing a leak check will slow down the opening When the dispenser switch is activated afterthe pressure time of a leak detector. Product that is lost due to has been bled to zero through the ball valve,the pressure contraction will be viewed by the leak detector the same must increase to full pump pressure (indicating that the as product lost due to a leak. If the leak detector is LLD has completed the line test)before the sound of the metering product into the line at a rate of 3 GPH and solenoid opening is heard. This test must be performed thermal contraction is occurring at a rate of 2 GPH, the with the bibcock closed. All solenoid valves in the system net pressurization flow into the piping system is only 1/3 must be checked for appropriate timing. as much or 1 GPH. Accordingly, the opening time is extended. The opening time will vary with the rate of IN SUMMARY, by using the previous ABC steps, it thermal contraction present at the time of the leak test. is possible to diagnose the reasons leak detectors are going into a restricted flow condition. The problem may 6) Are there minor product leaks in the system? be an inadequate solenoid delay time, prolonged test Leak detectors are designed to detect a leak of 3 time or both. If the delay time is sufficient for the leak GPH downstream of the leak detector. Leaks smaller detector to perform its test,uninterrupted flow will occur. than this will not necessarily result in restricted flow. To state it another way, if B and C are synchronized, However, a leak smaller than 3 GPH will affect the leak the leak detector will not cause interruption in flow even detector by prolonging the opening time. if the leak detector performs a leak test each time the If there are leaks greater than approximately 3 gph, pump is activated. If the system stays sealed long the leak detector will never open but will function as enough for the leak detector to complete the test, no described above. However, if there are leaks in the interruption of flow by the leak detectorwill occur regard- system which are less than approximately 3 gph,the leak less of the opening of nozzles. detector will eventually open, but, not in the prescribed However, if B and C are not synchornized, it is time. If small leaks are present while the leak detector probable that, periodically, the system will be open, meters 3 gallons of fuel per hour into the line,a portion of previous to the completion of the line test by the leak this fluid will leak out. The net effect will be a longer time detector and resulting in the restriction of flow by the leak for the leak detector to open. The nearer the leak is to detector. If the delay time is insufficient,or the test time zero, the nearer the time is to the normal test time. istoo long,or whether thermal effects,system resiliency, However, the nearer the leak is to 3 gph, the longer the internal leak detection seals, upstream pump seals or test time will be. From our experience, most of the small leaks occur actual system leaks are causing the line pressure to fall in the dispenser usually above the shear valve and below to zero, necessitating a line test by the leak detector,this the meter. Since the leak detector senses leaks down report will aid in determining the reason(s). -5-