A single-acting hydraulic cylinder uses a single 3/8"-18 NPT port to extend the plunger under 700 Bar (10,000 PSI) pressure and relies on either an internal tension spring (5–150 Ton) or structural gravity load (50–1,000 Ton) to retract—offering fast single-hose setup for general lifting. A double-acting hydraulic cylinder uses dual ports to power both extension and retraction hydraulically—mandatory for strokes up to 511 mm, horizontal/inverted pulling, high-tonnage bridge jacking (up to 1,000 Ton), and PLC synchronous lifting where long hose runs create return back-pressure.
1. Single-Acting Hydraulic Cylinders: Spring Return vs. Load (Gravity) Return
Single-acting cylinders connect to a 3-way/2-position pump valve via a single high-pressure hose. When hydraulic pressure is released at the pump, the plunger retracts by one of two mechanisms:
- Internal Spring-Return Cylinders (HSC, HSCF, HSCL, HSCH): A heavy-duty wound return spring inside the bore pulls the piston back automatically when oil pressure vents. The HSC Series spans 5 to 100 tons with 16 to 362 mm strokes across 41 models; HSCF Super-Flat cylinders fit into ultra-narrow gaps (8 models, 5–150 Ton, 6–16 mm stroke); HSCL Low-Height cylinders cover 10–100 Ton (38–62 mm stroke); and HSCT multi-stage telescopic cylinders (4 models, 10–50 Ton) deliver 25 to 64 mm multi-stage strokes from a low collapsed profile.
- Gravity / Load-Return High-Tonnage Cylinders (HSCX, HSC-LN, HSC-LNH, HSC-LP): Load-return cylinders (HSCX Series, 42 models from 50 to 1,000 tons, 50–300 mm stroke) rely on the weight of the supported bridge girder or structure to push oil back to the reservoir when the dump valve opens.
2. Double-Acting Hydraulic Cylinders: Powered Retraction & Relief Protection
Double-acting cylinders feature two 3/8"-18 NPT ports (a bottom advance port and an upper annular retract port) connected to a 4-way/3-position directional control valve, with an integrated retract safety relief valve to prevent over-pressurization:
- General-Purpose & Long-Stroke Double-Acting Cylinders (HDC Series): 18 models delivering 10 to 300 tons pushing force with strokes from 57 to 511 mm for press frames, horizontal skidding, and structural pulling.
- High-Tonnage Construction Double-Acting Cylinders (HDCX Series): 42 models delivering 50 to 1,000 tons with 50 to 300 mm strokes at 700 Bar, guaranteeing fast retraction even when unloaded or connected through 30-meter hoses on bridge piers.
- Hollow Plunger Cylinders (HSCH & HDCH Series): Single-acting HSCH (10 models, 13–100 Ton, 8–155 mm stroke) and double-acting HDCH (10 models, 30–150 Ton, 38–258 mm stroke) feature a center thru-hole for post-tensioning cables and tie-rod pulling.
3. Mechanical Lock-Nut Cylinders vs. Hydraulic Holding
Whenever a lifted bridge span, transformer, or turbine casing must remain supported for hours or weeks, engineers specify mechanical lock-nut cylinders (HSC-LN 42 models 50–1,000T, HSC-LNH 44 models 50–1,000T, HSC-LP Pancake 9 models 60–520T, or double-acting HDC-LN 24 models 50–300T). Rotating the threaded lock ring down against the cylinder body transfers 100% of the load to a solid steel column, allowing pump pressure to be vented to 0 Bar.
4. Engineering Selection Matrix: HydraStark 700 Bar Hydraulic Cylinder Families
| HydraStark Series | Acting & Return Type | Tonnage Range @ 700 Bar | Stroke Range | Primary Engineering Application |
|---|---|---|---|---|
| HSC Series (41 models) | Single-Acting, Spring Return | 5 – 100 Ton | 16 – 362 mm | General plant rigging, machinery lifting, fixture clamping |
| HSCF (8) / HSCL (5) / HSCT (4) | Single-Acting, Spring Return | 5 – 150 T / 10 – 100 T / 10 – 50 T | 6 – 16 mm / 38 – 62 mm / 25 – 64 mm | Confined gap alignment, low-clearance & multi-stage jacking |
| HSCX Series (42 models) | Single-Acting, Load Return | 50 – 1,000 Ton | 50 – 300 mm | Heavy civil vertical jacking where gravity returns the plunger |
| HDC (18) / HDCX (42 models) | Double-Acting, Hydraulic Return | 10 – 300 Ton / 50 – 1,000 Ton | 57 – 511 mm / 50 – 300 mm | Long strokes, horizontal pushing/pulling, PLC synchronous lifting |
| HSCH (10) / HDCH (10 models) | Single or Double-Acting Hollow | 13 – 100 Ton / 30 – 150 Ton | 8 – 155 mm / 38 – 258 mm | Center-hole cable tensioning, tie-rod pulling, bearing extraction |
| HSC-LN / HSC-LP / HDC-LN | Single or D/A + Mechanical Lock Nut | 50 – 1,000 T / 60 – 520 T / 50 – 300 T | 45 – 300 mm | Sustained mechanical load holding with zero hydraulic pressure |
Frequently Asked Questions (FAQ)
Why won't my single-acting load-return cylinder (HSCX or HSC-LN) retract when unloaded?
Load-return cylinders do not contain an internal return spring; they require external downward weight (or a shop press/strap) to push the plunger back into the bore after the pump dump valve is opened. If your application requires the plunger to retract quickly before the load is lowered onto it—or if hose lengths exceed 10 meters—specify an HDCX or HDC-LN double-acting cylinder instead.
What ASME safety standard governs 700 Bar industrial hydraulic cylinders?
All HydraStark 700 Bar hydraulic cylinders are designed and factory proof-tested to 125% of rated working pressure (875 Bar proof test) in accordance with ASME B30.1 safety standards for jacks and industrial lifting cylinders.
How much side load can a hydraulic cylinder tolerate?
Hydraulic cylinders are designed for axial loads; off-center side loading causes plunger galling and seal blowout. Always install a 5° swivel tilt saddle (such as the optional CATS100–CATS1000 tilt saddles on HSC-LN/LNH/HSCX cylinders, or integral tilt saddles on HSC-LP pancake cylinders) to keep eccentric side loads below 5% of rated cylinder capacity.