piston de refoulement à évent

OBS: Le volume compris entre le piston de poussée [...] et le piston de refoulement [...] communique éventuellement avec l'extérieur par au moins un évent [...], cet évent est percé à travers la partie aval [...] et le corps [...] et sert à évacuer l'air compris entre les deux pistons lors du fonctionnement.

CONT: Vented surge blocks are designed to allow fluids to bypass the block on the down-stroke of the surging process and to lift the fluid on the upward stroke. Advantages of using a vented surge block: less pressure is exerted on the formation; faster evacuation of the well; can be run on rods or a weighted line for faster service.
CONT: Surge Blocks.- Device that fits inside a well with a flexible gasket that is close in size to the inside diameter of the well. Attached to a rod that is raised and lowered with a stroke of about 3 feet. Surge block may be solid, vented or spring-loaded
CONT: The development process shall include surging and pumping the well. The surging shall be done by either a solid or valved surge block.