Wetstock Reconciliation at fuel storage facilities - Carrickfergus ...

5d. ii – Potential effects of Vapour Recovery Systems on wetstock reconciliationVapour recovery systems introduce pressure differences inside your tanks. The increased, or decreased, pressures can have adverse effectson tank measurements. Hydrostatic gauges are pressure based measurement systems and therefore have problems accounting for theeffects of vapour recovery systems. It is possible to get hydrostatic gauges balanced to work in tanks with vapour recovery systems.The effects of vapour recovery on tanks with dipsticks are illustrated below.Figure 5 Figure 6After delivery, pressure builds up in the tank. The compressedvapour in the tank forces the fuel to rise up the fill pipe, as thisis the point of least resistance. Any gauge or dipstick located inthe fill pipe will over-estimate the amount of fuel in the tank.As fuel is sold from the tank, the pressure drops and a partialvacuum can be created. As a result, the fuel level drops in the fillpipe as shown. Any gauge or dipstick located in the fill pipe willtherefore under-estimate the amount of fuel in the tank.This also applies for dipsticks located in diptubes.There is a potential overfill danger whentank contents are under-estimated.1 Use the correct dipstick for the tank and check that it is the correct length.2 Incorrect tank calibrations can have a significant effect on wetstock variance.3 Vapour recovery can affect stock readings where unbalanced hydrostatic gauges or dipsticks are in use.© Environment Agency11