FIELD: oil industry. SUBSTANCE: device has cylinder with radial bypass holes, spool loaded by spring, locknut, outer housing connected by threaded joints with upper and lower subs, and inner housing. The latter accommodates spring of spool. Spool is made in form of differential plunger. Radial channel of upper sub communicates with string-borehole annulus. Axial channels of sub are arranged on circumference and intended to pass produced liquid. Central axial channel communicates with radial channel and space of inner housing Made on circumference of lower sub are axial channels to pass produced liquid and central axial channel and radial channel which are placed in communication. Indicated channels communicate with casing string space below electric pump. Central channel of lower sub is overlapped by end face of differential plunger. When dynamic head drops, pressure differential acting on plunger makes the latter move upwards. As a result, hole in cylinder gets opened and liquid bypasses into string-borehole annulus to restore required level, after which plunger overlaps axial channel of lower sub again, and liquid is delivered by pump to surface. EFFECT: enhanced reliability of operation. 4 cl, 4 dwg
