Frequently Asked Questions
Q1: Can this A4VSO500DR be used as a hydraulic motor? Can it pump water?
❌ Not usable as a motor: The A4VSO is designed exclusively as a pump for open-circuit operation. Driving it in reverse as a motor will not produce useful torque and will cause internal damage.
❌ Strictly prohibited for pumping water: Axial piston pumps rely on oil film lubrication between moving parts (pistons/cylinder barrel/valve plate). Water will:
- Destroy lubrication -> immediate seizure of copper-steel friction pairs
- Cause corrosion and rusting of precision surfaces
- Swell standard NBR seals, causing leakage
For high-pressure water applications, use dedicated plunger pumps or centrifugal pumps -- never a hydraulic piston pump.
Q2: What is the difference between DR, DFR, and LR2 control? When should I choose DR?
DR (this model): Pressure compensator only. Below set pressure -> full flow; at set pressure -> pump de-strokes to maintain constant pressure (delivering only leakage compensation flow). Best for: Simple pressure-limiting systems (presses, power units) where load sensing is not needed.
DFR / LR2: Adds Load Sensing (LS) function. The pump maintains a constant differential pressure (∆p ≈ 14-18 bar) between pump outlet and the LS signal from the valve bank, delivering only the flow demanded by the system. Best for: Multi-actuator valve-controlled systems (injection molding, machine tools) where energy saving matters.
When to choose DR: Your system has no LS signal line, requires only pressure limitation, or simplicity/reliability is prioritized over energy efficiency.
Q3: How do I verify counter-clockwise rotation (30L)? What happens if I run it backward?
L = Counter-Clockwise (CCW): Facing the drive shaft end (coupling side looking into the pump), the shaft must rotate
counter-clockwise.
Verify by checking the motor/engine rotation arrow (usually stamped on the fan cover) or perform a brief jog test.
❌ Reverse rotation will cause catastrophic failure within seconds:
- The internal port plate is asymmetrical -- reverse rotation misaligns suction and pressure ports
- Lubrication passages are directional -- loss of lubrication causes immediate seizure
- Cavitation and dry running destroy the cylinder barrel/piston assembly
If rotation is wrong, swap motor phases or replace with an "R" (clockwise) pump. Never attempt to run in reverse.
Q4: What are the critical suction (inlet) requirements for this 500 cc pump?
Large displacement pumps are extremely sensitive to inlet conditions:
- Minimum absolute inlet pressure ≥ 0.8-1.0 bar (gauge ≈ −0.2 to −0.1 bar max vacuum).
- For speeds above 1200 rpm, a boost pump / charge pump providing 1.5-2 bar positive head is strongly recommended.
- Suction line design:
- Inner diameter ≥ DN80 (DN100 preferred)
- Length as short as possible (< 1.5 m), minimize elbows
- Dedicated 100 mesh (149 µm) suction strainer with pressure loss < 0.05 bar
- Tank outlet should be above pump inlet or submersion depth > 300 mm.
Cavitation symptoms: high-frequency noise, pitting on valve plate, flow reduction, premature bearing failure.
Q5: How should the case drain be connected? What if I ignore it?
Case drain carries internal leakage for
cooling and flushing wear debris.
Must be routed via a
dedicated line directly to the reservoir (no shared return lines).
Backpressure must be ≤ 0.5 bar (ideally 0 bar). The second drain port must be plugged.
❌ Never:
- Block the drain port
- Connect to a pressurized return line
- Share a long small-diameter return line with other components
Consequence of blocked/pressurized drain: Housing pressure buildup -> shaft seal blowout, valve plate distortion, bearing overheating, and total pump failure.
Q6: What drive motor power is required?
At 350 bar / 1200 rpm / full displacement:
- Hydraulic power Pₕ = (500 × 10⁻⁶ × 350 × 1200) ÷ 600 ≈ 350 kW
- Including mechanical efficiency (η ≈ 0.90-0.92) -> shaft input ≈ 380 -390 kW
➡
Recommended drive: 400 kW (≈535 HP) electric motor with:
- Adequate starting torque for 400 bar peak conditions
- S1 continuous duty rating
- Speed matching the pump's optimal range (avoid prolonged operation below 750 rpm)
Q7: Can standard NBR seals handle HFC (Water Glycol) or HFD (Phosphate Ester)?
✅ HFC (Water Glycol): NBR is acceptable but requires:
- Pressure/temperature derating per Rexroth guidelines (typically pressure × 0.8, Tmax limit +5 °C)
- Reduced lubricity of HFC -> shorter oil change intervals
❌ HFD (Phosphate Ester): NBR will swell and degrade rapidly ->
FKM (Viton) seals are mandatory (specify /V suffix or FKM option when ordering)
Mineral oil (HL/HLP) is the standard intended fluid for this model -- no special measures needed.
Q8: What are the essential commissioning steps?
- Fill and vent: Loosen case drain fitting and high-pressure port bleed screw. Manually rotate shaft while filling until oil emerges without bubbles.
- Confirm case drain return: Verify drain line is connected to tank and unobstructed.
- Jog for rotation check: Briefly energize motor to confirm CCW (L) rotation. Listen for abnormal noise.
- Low-pressure run-in: Back off DR adjustment screw (reduce pressure setting). Run at low pressure while cycling system to purge air.
- Gradual pressurization: Slowly turn DR screw clockwise to raise pressure to target. Monitor noise, temperature, and case drain flow.
- Lock and record: Once set, tighten lock nut and record the pressure setting for future reference.
For other Rexroth models (A10VSO, A4VG, A11VO, A2FM motors, proportional valves, amplifiers, valve blocks), please provide the complete model number.