Spec the HPU to the actuator's worst-case load, not the average: pressure 21 MPa with single-acting DC packs and 35 MPa on industrial AC units define the two common operating envelopes buyers see from Chinese OEM catalogues [S4][S1].
Match reservoir size, pump displacement, motor power, and valve logic to duty cycle, ambient temperature, and cleanliness class; a hydraulic power unit is the integrated package of motor, pump, tank, valves, and often cooling and filtration, and every sub-system has a separate sizing rule that has to reconcile.
Define the HPU and the Five Sub-Systems You Are Actually Sizing
An HPU (Hydraulic Power Unit) is not a single product but a stack: electric motor or engine prime mover, pump (gear / vane / piston), reservoir, valve manifold, and ancillaries (filtration, cooling, level/temperature switches, pressure relief, accumulator) [S1][S7]. Industrial AC and DC units are catalogued as separate families, with DC mini units at 12/24 V and 150–800 W, and industrial AC power units covering higher pressure / flow duties [S1][S4].
The Mocen DP11 family illustrates the lower envelope: 21 MPa max, DC 12/24 V, 150–800 W, driving single-acting cylinders with three return-flow options (non-adjustable, pressure-compensated non-adjustable, adjustable) and three 2-way valve options (manual, solenoid, solenoid with manual override) [S4]. SMD's Curvetech line shows the upper envelope: oil-filled submersible HPUs for work-class ROVs, trenchers, ploughs, and dredge systems, designed to minimise weight and unit size without compromising on long-term subsea reliability [S3].
Between these extremes sits the dominant industrial pattern: AC motor, internal gear pump, steel reservoir, cartridge valve manifold, and a pressure relief set to the system's working pressure. The variant you pick is governed by the actuator's load profile, not the brand list.
Selection Criteria: Pressure, Flow, Duty Cycle, Cleanliness, Noise, Certification
Pressure class is the first gate. Subsea and heavy industrial units commonly work at 21–35 MPa (roughly 3000–5000 psi); ROV HPUs are sized to the work-class vehicle's tooling circuit, often in the 20–30 MPa band with flows up to tens of L/min depending on thruster and manipulator demand [S3]. The Mocen DP11 caps at 21 MPa, which is a hard ceiling on cylinder bore if the load demands more [S4].
Flow is the second gate. It is governed by pump displacement and motor speed; for a 150–800 W DC pack driving a single-acting cylinder, expect single-digit cc/rev gear pumps and short duty cycles (intermittent, with thermal limits enforced by reservoir size) [S4]. Industrial AC units, by contrast, can run 4–25 cc/rev gear pumps or piston pumps at 1450–1750 rpm, producing tens of L/min continuously.
Duty cycle drives cooling and reservoir sizing. Intermittent duty (1–2 cycles per hour) is fine with a small tank and natural convection; continuous duty at high pressure requires a heat exchanger, larger reservoir, and derated pump. A common undersizing error is to specify an intermittent-duty mini unit for a press or lift that runs every few minutes, which cooks the fluid and trips the relief.
Cleanliness class and fluid type matter. Industrial ISO 4406 cleanliness targets (e.g. 18/16/13 for general hydraulics, 16/14/11 for servo) should be set before pump type: piston pumps are far less tolerant of contamination than gear pumps, and servo/proportional valves are stricter again. Subsea HPU fluids include environmentally acceptable options in some applications, but the ROV and trenching space typically runs mineral or synthetic oils compatible with subsea seals [S3].
Noise, ingress protection, and certification close the list. Compact DC units with fully enclosed aluminium housings can reach IP68 and "low noise" ratings for cabinet or outdoor installation, working stable in worst-case weather [S7]. Industrial HPU noise typically runs 65–80 dB(A) at 1 m without a sound enclosure; ATEX/IECEx certification is mandatory for Zone 1/2 and Group I M2 environments, and aircraft ground HPUs are governed by aviation GSE standards through suppliers such as Hydro [S6].
Variant Map: AC, DC, Mini, Industrial, Subsea, Ground Support
Six variants cover almost every industrial query. They differ on prime mover, pressure, duty, and certification, and they do not interchange cleanly. [S1]
DC mini power packs (12/24 V, 150–800 W, 21 MPa, single- or double-acting, IP68 enclosures) suit mobile equipment, cabinet-mounted actuator drives, RV / tail-lift / snow plough applications where mains power is unavailable [S4][S7]. AC power units (1.5–30 kW typical, 21–35 MPa) handle workshop machinery, machine tools, lifting tables, and factory automation, usually with cartridge valve manifolds and steel tanks [S1]. Bi-rotational power units add a motor or cylinder that must turn in both directions, with separate flow paths [S1][S7].
Industrial power units scale up to 50–200 L reservoirs, multi-section gear pumps, and heat exchangers for presses, injection moulding clamps, and steel mill hydraulics [S1]. Subsea / ROV HPUs are oil-filled, pressure-compensated, submersible, and built to minimise weight and volume while delivering long-term reliability for trenchers, ploughs, and dredge systems [S3]. Ground-support aircraft HPUs are the most specialised: Hydro distributes TEST-FUCHS HGUs covering regional, narrow-, and wide-body aircraft with system pressures up to 30 MPa and specific flow / cleanliness profiles matched to the airframe [S6].
A criteria-based comparison of the four most-asked options:
DC mini (Mocen DP11 / ATS-31 family): pressure 21 MPa max, power 150–800 W, reservoir sub-5 L, IP68 aluminium housing, intermittent duty, no certification overhead, low cost [S4][S7]. AC industrial (Target / SN Hydraulics / generic Chinese OEM): pressure 21–35 MPa, power 0.75–22 kW, reservoir 10–200 L, cartridge manifold, natural or forced-air cooling, noise 65–80 dB(A), ATEX/IECEx optional [S1][S5]. Bi-rotational industrial: same envelope as AC industrial but with reversible pump or dual-circuit logic; adds cost and complexity for synchronised rotation [S1][S7]. Subsea / ROV: pressure 20–30 MPa typical, oil-filled and pressure-compensated, weight-optimised, very long qualification cycle, very high unit cost, and a customer base limited to work-class ROVs, trenchers, ploughs, and dredges [S3].
Who an HPU Is For, and Who Should Buy Something Else
An HPU is the right answer when the load is intermittent or continuous-duty, the system pressure is in the 15–35 MPa band, the actuator is hydraulic (cylinder or motor), and a centralised reservoir / pump room is acceptable. That covers most factory automation, mobile equipment, lifting, clamping, and subsea tooling circuits [S1][S3][S4].
Skip the HPU and consider an electro-mechanical actuator (EMA) or electric linear actuator when the duty is light, the cycle count is low, the environment demands zero oil leakage (food, pharma, clean rooms), and the cost of hydraulic infrastructure is not justified. Electro-hydraulic actuators (EHAs) replace the HPU with a local motor-pump-cylinder block and make sense for aerospace and isolated jacking points, but they are a different procurement class entirely.
Avoid the mainstream "AC industrial, 21 MPa, gear pump, 50 L tank" answer when the duty is high-cycle continuous, the cleanliness demand is servo-grade, or the environment is explosive: in those cases you need a piston pump, larger reservoir or heat exchanger, and ATEX/IECEx certification with the right temperature class and gas group [S1]. The standard applies to the whole assembly, not just the motor.
Real Use Cases and the Spec Behind Each
DC mini pack on a single-acting lift: 21 MPa max, 12 or 24 VDC, 150–800 W, manual or solenoid 2-way valve, return flow via flow control with optional pressure compensation, IP68 housing for outdoor or wash-down locations [S4][S7].
Bi-rotational industrial unit on a rotary index table: AC motor, reversible pump or dual solenoid logic, double-acting circuit, 21–35 MPa working pressure, cartridge manifold with speed and pressure control, 20–60 L steel tank [S1][S7].
ROV / subsea HPU on a work-class vehicle: oil-filled and pressure-compensated for long-term submersion, electric drive to minimise exhaust and noise, sized to the vehicle's thruster and manipulator peak demand (often 20–30 MPa, multiple tens of L/min), and qualified for the vibration and shock profile of the host [S3].
Aircraft hydraulic ground power unit: aviation-grade fluid cleanliness, system pressure up to 30 MPa, versions for regional, narrow-, and wide-body aircraft, used for testing and maintenance of mainline hydraulic systems where compromise is not permitted [S6].
General factory press or clamp: 7.5–22 kW AC motor, internal gear pump, 100–200 L steel reservoir, cartridge valve manifold, air-cooled heat exchanger, pressure relief set to system working pressure, level and temperature switches wired to the machine PLC [S1][S5].
Limits, Failure Modes, and Sourcing Discipline
Common failure modes trace back to spec gaps: undersized reservoir (fluid foaming and cavitation at high cycle rates), undersized pump (relief valve chatter and overheating), wrong cleanliness class (piston pump or proportional valve wear within months), and missing certification (rejected at commissioning in a Zone 1 plant). Subsea HPUs add their own failure surface: seal degradation under long-term submersion and pressure-compensation failure on long storage [S3].
Vendor landscape, 2026-08: Ningbo Target Hydraulics publishes a full AC / DC / mini / bi-rotational / industrial stack with manifold, cartridge valve, and reservoir SKUs, positioning as a 10-year hydraulic components specialist [S1]. Mocen sells the DP11 and ATS-31 mini families with documented 21 MPa, 12/24 V, 150–800 W, IP68 specifications, and three valve / three return-flow options for each base model [S4][S7]. SN Hydraulics in Mumbai covers the Indian industrial and mobile-equipment customer base with cylinder and power-pack manufacturing since 2012 [S5]. Hydro distributes the TEST-FUCHS HGPU line for aircraft ground support across regional, narrow-, and wide-body types [S6]. SMD (UK) produces the Curvetech subsea HPU range for work-class ROVs, trenchers, ploughs, and dredge systems [S3]. Ringspann lists hydraulic power units as an accessory for industrial brake systems, where the HPU is a sub-component rather than a standalone product [S2].
Sourcing checklist before purchase: confirmed working and max pressure, pump type and displacement at rated speed, reservoir volume with thermal model, valve manifold schematic, IP rating, ambient temperature range, noise at 1 m, and the certification dossier (ATEX/IECEx zone and group, CE, or aviation GSE standard) [S1][S3][S6]. Reject quotes that list only "max pressure" and "motor power" without duty cycle, cleanliness class, and noise.
For Chinese OEM sourcing, audit the bill of materials, request a schematic that matches the manifold plate, and confirm whether the cartridge valves are name-brand (Sun, Hydraforce, Atos) or house-brand; the difference shows up in seal kit availability and lead time, not on the data sheet.
Shortlist Logic and a Cross-Reference to the Encyclopedia
Use the following decision sequence: (1) identify actuator type and worst-case load; (2) calculate required pressure, flow, and duty cycle; (3) set cleanliness and noise targets; (4) choose variant (DC mini, AC industrial, bi-rotational, subsea, aviation GSE); (5) confirm certification and ambient; (6) match reservoir and cooling to thermal model; (7) verify spare-parts support for cartridge valves and pumps. [S1]
For a primer on the broader hydraulic circuit the HPU feeds, see the encyclopedia entry on hydraulic systems and the related pages on the hydraulic power unit, hydraulic actuators, and the FRL unit that conditions the air supply where pneumatic logic is also in the loop. Buyers comparing a packaged power unit against a discrete sand reclamation unit for foundry hydraulics, or a degassing unit downstream of the reservoir, will find the variant map in this article lines up with the duty-cycle and cleanliness rules covered there.
For the broader Chinese OEM landscape that intersects with HPU motors and pumps, the hydraulic motor suppliers 2026 map and the hydraulic cylinder suppliers 2026 shortlist carry the same variant-and-spec discipline. Buyers matching an HPU to a downstream pneumatic or hydraulic actuator should cross-check the packaging machinery supply chain 2026 spec gates for duty-cycle benchmarks in continuous-motion plants.