Abstract: A delivery vehicle is used to deliver oil with or without a marker and is provided with apparatus which includes a reservoir of marker and an injector pump for adding marker to the oil. A controller records the occurrence of an event associated with the depletion of the reservoir which has an upper section, a lower section and a marker level sensor located at a narrow constriction between the two sections. The apparatus includes a blender which causes fluid flow to occur at different rates and is operable so that the slugging effect of marker injection is reduced. The injector pump is arranged to provide a delay prior to each forward or reverse stroke. The memory devices of the controller are locked or sealed so as to deny access to reprogram the controller.

Abstract: An apparatus for adding an additive, such as a marker, to a base fluid, such as oil, includes a blender having a receptacle or diffusion chamber in which mixing of the additive and the base fluid occurs. The additive is injected in discrete amounts. Resistances to fluid flow in the receptacle or chamber cause fluid flow to occur at different rates in order to reduce the slugging effect caused by additive injection in discrete amounts.