Said flow restrictor(3) comprises inlet and outlet and has one or more flow restricting holes.

The maximum orifice diameter of said flow restrictor(3) is greater than that of the filter membrane(2), and the total permeation capacity of the flow restrictor(3) is less than that of said filter membrane(2).

Apparatus (10) further includes an outlet (34) for releasing raffinate including a flow controlling restriction (38).

The string is set in the wellbore with the flow restriction device adjacent the producing formation.

This is achieved by transporting the superheated liquid against a flow restrictor, e.g. an orifice plate.

The liquid which is expanded and partially evaporated on passage through the flow restrictor is returned to the distillation column.

Methods of providing pressure relief by flowing fluid past a flow restrictor are also disclosed.

A make-up flow Channel engages the main channel at a position between the hydrodynamic flow restrictor and the output channel.

By this arrangement the amount of particles and air-bubbles entering the narrow flow restrictor will be reduced.

A hydrodynamic flow restrictor is positioned in the main channel, which substantially negates the hydrodynamic backpressure in the main channel to the extent that low electroosmotic flow may be utilized.

Each port (40) is adapted to receive a flow restrictor to permit selective control of velocity and flow volume of the liquid through the down tube (24).

Actual opening and closing of the flow restrictor is determined by symptoms from either excessive or inadequate CSF diversion.

More specifically, the invention relates to a safety arrangement reducing the risks associated with diminished flow resistance through the flow restrictor.

The apparatus includes a completion string which contains a flow restriction device, a crossover device and a packer each above and below the crossover device.

To provide a desired drug flow rate, the primary fluid is forced from a first reservoir through a flow restrictor into a second reservoir displacing a portion of the drug reservoir, thereby expelling the drug from its reservoir.