Rotary Drilling Pressurized Cylinder
Push Down to Drill, Pull Up to Extract — The Cylinder That Never Rests
Every borehole is a cycle of penetration and extraction. The rotary table spins the drill tool, and the pressurized cylinder pushes the power head downward along the mast — applying "crowd force" that drives the tool into the soil. When the drilling bucket is full (1–3 cubic metres of earth), the cylinder reverses: it lifts the power head upward, pulling the kelly bar, drill string, and soil-laden bucket out of the borehole. The operator swings the bucket over the spoil pile, opens it, dumps the soil, swings back, and the cycle repeats.
On a typical foundation piling job, this cycle takes 3–8 minutes and repeats 50–150 times per pile. A rig drilling 3–5 piles per day performs 150–750 crowd-and-extract cycles daily. The pressurized cylinder is the hardest-working cylinder on the drilling rig — cycling continuously throughout the entire working day with full force in both directions.
Korea Ever-Power manufactures the pressurized cylinder as the final component of the three-cylinder rotary drilling rig hydraulic cylinder system — alongside the luffing cylinder (#24) and the mast cylinder (#25).
Technical Specifications
| Parameter | Specification |
|---|---|
| Product | Rotary Drilling Pressurized Cylinder |
| Function | Control the lifting and lowering of the power head |
| Bore Diameter | 125 mm – 210 mm |
| Rod Diameter | 90 mm – 150 mm |
| Stroke | ≤ 8,500 mm (longest in range) |
| Working Pressure | Up to 35 MPa |
| Application | Rotary Drilling Rig (foundation piling) |
| Certification | ISO 9001 · 100% hydrostatic tested |
8,500 mm Stroke — Why the Power Head Must Travel the Full Mast Length
The power head sits on a carriage that rides up and down the mast on guide rails — like an elevator on its shaft. The pressurized cylinder's stroke determines how far the power head can travel along the mast, which directly determines the maximum single-pass drilling depth:
Each downward stroke of the pressurized cylinder advances the drill tool one "pass" into the earth — typically 1–4 metres per pass depending on soil conditions. The kelly bar (a telescopic square or hexagonal shaft) extends as the power head descends, reaching deeper with each successive section. The 8,500 mm cylinder stroke matches the kelly bar section length, ensuring the full drilling depth of each kelly section is utilised in a single pass.
After each pass, the cylinder retracts to lift the power head, kelly bar, and soil-laden bucket back to the mast top. The extraction force must overcome the combined weight of the drill string plus the friction of the bucket walls against the borehole walls — potentially 15–30 tonnes pulling upward. The annular piston area (bore² − rod²) × 35 MPa must produce enough retraction force for the heaviest soil load. Contact Korea Ever-Power engineering for crowd/extraction force calculations.
Drilling Mud, Bentonite, and Concrete — The Harshest Contamination on Any Cylinder
The pressurized cylinder's exposed rod section — up to 8,500 mm of chrome surface cycling in and out of the barrel — operates in the most contaminated environment of any cylinder in the mobile machinery range. Drilling rigs use bentonite slurry (a clay-water mixture) to stabilise boreholes, and this slurry coats every surface of the rig during operation. Bentonite is abrasive when it dries and highly adhesive when wet — it clings to the rod surface and can be dragged past the wiper seal into the barrel.
On piled foundation sites, concrete slurry from the pile-pouring process adds a further contamination threat. Cement particles that enter the seal zone harden within hours — creating an abrasive paste that destroys the seal lip and scores the rod chrome.
Korea Ever-Power specifies a triple wiper system for the pressurized cylinder — primary wiper + secondary wiper + buffer seal — with a mud-guard boot covering the rod's exit point. Chrome plating thickness is 80 µm minimum (the heavy end of the range) to provide maximum resistance to abrasive contamination.
Manufacturing Process
The 8,500 mm stroke requires an overall cylinder length exceeding 9,000 mm when retracted — among the longest single-stage cylinders Korea Ever-Power produces. Deep-hole boring (for barrels where seamless tube is not available), precision honing to Ra 0.2–0.4 µm, and rod straightness ≤0.1 mm/metre across the full 8.5-metre rod are performed on dedicated long-stroke machining centres. The rod's chrome plating is applied in a vertical plating tank specifically designed for rods exceeding 6 metres.
Seals are polyurethane piston seal + triple wiper + buffer seal stack, rated for -30 °C to +80 °C and 35 MPa. The cylinder is hydrostatic tested at 1.5× rated pressure (52.5 MPa) and full-stroke cycled 10 times to verify smooth operation across the entire 8,500 mm travel — checking for stick-slip, seal drag, and rod deflection at full extension.
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