Pumps priming adjustable device, realized with an ejector provided of a suction inlet and an outlet communicating through a conduit for conveying and exhausting a fluid that has been aspired from a pump or from its suction pipe, using the vacuum effect created inside the ejector itself by the flow of compressed air. The suction inlet of said ejector communicating with the pump and/or the pipe through an on-off valve which, with its opening and closing action, permits the flow of fluid aspired from pump or from its pipe into the said ejector or prevents such flow.
To permit the operation of ejector is also provided an external source of compressed air connected to a feeding valve of the ejector, and between said suction inlet and said outlet there is an injection nozzle injecting compressed air into the conduit, having the injection nozzle a predetermined flow section.
The injection nozzle is adjustable in said flow section, which consists of an annular channel in the peripheral wall of said conduit, which in turn being composed of two parts, a first part static and a second part movable, which may be moved towards and/or away from each other to change the flow section of the channel of injection nozzle.