Variable Diameter Hole Opener

Variable diameter hole opener is can also expand the well hole when drilling, it can save the trip out and drill down time, improve drilling efficiency. This under reamer is hydraulic expansion type, it’s convenient to control the open and close of tool arm.

Structure and principle of Variable Diameter Hole Openers

Variable diameter hole openeris composed of body (1), top connection (2), cutter (3), rotor arm (4), piston connector (5), piston collar (6), nozzle collar (7), seal ring I (8), set screw (9), spring(10), piston(11), left slide block (12), right slide block (13), clamp spring (14), nozzle (15), seal assembly body (16), backing up screw (17), piston outrigger shaft (18), pin roll (19), short screw (20) etc.

Each part is made of high quality alloy steel by heat treatment and precision machining, solid and reliable, high intensity, can be used under hostile drilling environment. Each rotor arm fixed a set of replaceable cutter. The cutter can be replaced by hand on the drilling panel easily and convenient. Three directional jet fixed with replaceable nozzles can clean the drill hole well and extend the service life of the cutter. The nozzles fixed by clamp spring is convenient for replacement.

Variable diameter hole openeruse piston rod connect rotor arm, through the liquid pressure difference to make the expansion, use compression loss to reset. During normal drilling, use liquid pressure difference to push piston connector and piston move in vertical then drive the rotor arm open, following drilling tools’ rotation, rotor arm cut and expand hole, spring is expressed; When the pump off, the expressed spring reset drive the piston rod rest, then the rotor arm go back to body. This under reamer rotor arm is easy to control, replace and maintenance, also the alloy steel roller improve the cutting efficiency.

Specification of Variable Diameter Hole Openers


Ream Range(inch)

ID mm(inch)


OAL mm(inch)


(8 1/4" ~ 13")

44.5(1 3/4")

4 1/2REG


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