DC Hydraulic Power Unit

DC hydraulic power unit is the heart of PTO-free mobile hydraulics, not accessories.

HCIC PU-series units are fully built in Jinan — no outsourcing, no white label. Each uses our in-house wound motor, load-matched gear pump, and valve blocks machined on our cylinder CNC equipment.

Running on 12V/24V truck batteries, it powers cylinders for dump trailer hoists, scissor lifts and tilt decks. No PTO or running engine; simply hook up cables and hoses.

Typical failures come from undersized wiring, trapped air or misadjusted relief valves. Every unit is load tested 3 minutes at 110% pressure. Units with over 8% amp draw surge get recalibrated.

I. Product Breakdown — What You Actually Get

1.1 The Motor

We wind our own DC motors. 2-pole series-wound, Class H insulation rated to 180°C. The PU-2000 runs a 2.0 kW motor. The PU-4500 runs a 4.5 kW motor. The difference is not just power — it is duty cycle.

A 2.0 kW motor on a 12V system pulls roughly 200 amps at full load. Most truck batteries can handle that for 30-45 seconds in normal weather. Below -10°C, you want the 4.5 kW motor on a 24V system. Cold oil is thick. A marginal motor will stall.

The armature is dynamically balanced to G6.3 tolerance. We check every motor on a Megger at 500V DC before assembly. Insulation resistance under 20 MΩ = reject.

1.2 The Pump

Gear pump. Aluminum body. Hardened steel gears, ground to a 0.8 μm Ra surface finish on the tooth flanks.

Displacement ranges:

• PU-2000: 1.2 cc/rev to 3.2 cc/rev
• PU-3000: 2.5 cc/rev to 5.0 cc/rev
• PU-4500: 4.0 cc/rev to 8.0 cc/rev

Why this matters: flow rate = displacement × motor RPM. A 3.2 cc pump at 2800 RPM gives you about 9 liters per minute. That determines how fast your cylinder moves. A 40-inch stroke cylinder with a 4-inch bore needs roughly 8.2 liters to extend fully. At 9 L/min, that happens in about 55 seconds. Change the pump displacement and you change that speed. Simple math. No magic.

1.3 The Valve Block

CNC-machined from 6061-T6 aluminum billet. Not cast. Cast bodies have porosity. We learned that in 2005 after a batch of 200 units came back with hairline cracks propagating from casting voids.

Standard configuration:

• One check valve (poppet type, hardened seat)
• One relief valve (direct-acting, adjustable from 10 to 25 MPa)
• One lowering solenoid valve (NC, 12V or 24V coil)
• SAE #6 or #8 work ports

The relief is set and sealed at the factory to 1.1× the system's rated pressure. We use a nitrogen-charged test stand, not a dead-weight tester. Dead-weight testers are fine for calibration labs; they do not catch dynamic cracking pressure drift.

1.4 The Reservoir

Horizontal-mount steel tank. 2 mm wall. Powder-coated inside and out. Internal baffle plate to reduce oil slosh on uneven ground.

Capacities: 4L, 6L, 8L, 12L, 15L.

The breather cap has a 40-micron filter element. You would be surprised how many units fail because someone lost the breather cap and dirt got in. A grain of sand at 150 microns will score a gear pump housing in about 20 cycles.

II. Technical Specifications

III. Application Scenarios

3.1 Dump Trailers (2-10 Ton)

This is 70% of what our PU-series ships for. A single-axle 5-ton dump trailer with a 4-stage telescopic hoist needs roughly 16 MPa to break the load at 45° tilt angle. The PU-3000 at 20 MPa gives a 25% margin. That margin matters when the load is wet sand, not dry gravel.

The unit mounts on the trailer tongue, inside a steel enclosure. Cable run from battery to motor should be 35 mm² minimum for runs under 3 meters. We include a 200A contactor relay with every unit. Do not skip the relay. You will weld the solenoid contacts in the manual controller.

3.2 Car Haulers / Tilt Deck Trailers

Lower flow requirement. A single-stage 3-inch bore cylinder running a 24-inch stroke needs about 2.8 liters to extend. At 5 L/min from a PU-2000 with a 2.0 cc pump, that deck tilts in roughly 34 seconds. Smooth enough that the car does not lurch.

3.3 Scissor Lifts & Service Truck Cranes

These applications demand holding. When the cylinder stops, it must stay stopped — no creep, no drift over 8 hours. We spec a pilot-operated check valve on the valve block for these orders. The poppet seats against a lapped surface. Leakage at 80% rated pressure: less than 0.1 cc per minute.

3.4 Compatible Hoist Models

Our PU-series is pre-matched to HCIC power hoist cylinders:

IV. FAQ

V. Manufacturing — How We Build It

The motor housing starts as a 1050 steel tube. We cut it, face both ends, and bore the stator seat to H7 tolerance on a CNC lathe. The stator is pressed in with a 0.02 mm interference fit. Too loose and it vibrates. Too tight and it cracks the housing in cold weather.

Pump gears are hobbed from 20CrMnTi, then carburized to 0.8-1.0 mm case depth at 58-62 HRC. The gear housing is honed to a 0.4 μm Ra bore finish. Gear tip clearance: 0.06-0.10 mm. Below 0.06 mm and thermal expansion locks the gears. Above 0.10 mm and volumetric efficiency drops below 85%.

Every assembled unit goes on the test bench. We log:

• No-load current draw (baseline for that motor/pump pairing)
• Flow rate at 10 MPa back-pressure
• Relief valve cracking pressure
• Internal leakage at 80% rated pressure (hold for 30 seconds)
• Amp draw at full load

All data goes into a serial-numbered test sheet. You get a copy with the unit.

VI. About HCIC 

HCIC has been building hydraulic products since 1998. 300+ staff. Three factories in Shandong Province. 54+ million USD in annual sales. Products shipped to 50+ countries.

We are not a trading company. We own the CNC lines, the welding cells, the honing machines, and the test benches. When you email us about a hydraulic power unit, you are talking to the people who machined the valve block, not a middleman who has never seen the inside of a pump.

Our R&D team includes 10 engineers with 15-25 years each in hydraulics. We do not just copy competitor designs. When a customer sends us a failure report, our engineering team does a full dissection — metallurgy, surface finish, dimensional inspection — and issues a corrective action within 14 days.

ISO 9001:2015 certified. QPQ nitriding line in-house. Salt spray testing to ASTM B117.

We also manufacture:

• Double-acting telescopic cylinders (waste handling, dump trailers)
• Tarp system cylinders
• Welded cross-tube cylinders
• Tie-rod cylinders (AG and industrial)
• Snow plow cylinders
• Custom hydraulic manifolds and valve assemblies