A4VSO355DR/30L-PPB25N00 Piston pump German Rexroth A4VSO355

Model Code Decoded:

• A4VSO = Open‑circuit swashplate variable pump

• 355 = 355 cm³/rev displacement

• DR = Pressure compensator (direct‑operated)

• /30 = Series 30

• L = CCW rotation

• P = Keyed shaft

• P = NBR seals

• B = ISO 4‑bolt flange

• 25 = SAE flange side ports (vs. 13 = BSPP threaded)

• N00 = No through‑drive

Frequently Asked Questions (FAQ)

Q1: What is the function of the "DR" control and when should I choose it over DRG or DFR1?

A: DR​ is a direct‑operated pressure compensator — you set the cut‑off pressure mechanically with the handwheel on the pump controller. When system pressure reaches that setpoint, the pump automatically reduces displacement (destroke) to maintain pressure with near‑zero flow. It is the simplest and most cost‑effective option for constant‑pressure systems.

• DRG​ = DR + remote pilot port (X) to shift pressure setpoint externally — choose if you need two or more pressure stages switched by a solenoid valve.

• DFR1​ = Pressure + Flow (Load‑Sense) controller — choose for energy‑saving systems where flow demand varies with load and you want constant Δp across an orifice.

Use DR when you only need one fixed pressure setting and no remote control.

Q2: This model is "L" (counter‑clockwise). Can I use an "R" (clockwise) version instead?

A: Only if your electric motor or engine can be reversed. "L" = CCW when looking at the shaft end; "R" = CW. The pump body and port positions are the same, but rotation direction is not interchangeable​ once ordered. Always confirm motor rotation direction before specifying — mismatched rotation will not damage the pump immediately but will reverse flow direction vs. expectation and may cause priming issues.

Q3: Is a case drain line required? How exactly should it be plumbed?

A: Yes — mandatory.​ The A4VSO has internal leakage that must be returned to tank:

• Connect the L‑port (case drain)​ directly to the tank, preferably above the oil level​ or via a standpipe ≤ 0.5 bar backpressure.

• Do NOT​ tee it into the suction line (risk of aeration and seal blow‑out).

• Route it to the tank before the suction strainer or to a clean‑side tank return header.

• Fill the pump case with clean hydraulic oil before first start‑up to prevent dry start damage.

Q4: What is the difference between port code "25" and "13"? What fittings do I need?

A:

• "13"​ = Side ports with metric BSPP (G‑thread)​ — needs threaded adaptors and bonded seals.

• "25" (this model)​ = Side ports with SAE 4‑bolt flanges​ — Pressure port typically SAE Code 61 (6000 psi) flange, Suction port SAE Code 62 (3000 psi) flange. You need SAE split‑flange halves + O‑rings (AS568‑xxx), not threaded fittings.

Confirm your hose/hardline termination matches SAE flange before ordering.

Q5: Can this pump be used in a closed‑loop hydrostatic transmission?

A: No.​ The A4VSO series is designed exclusively for open‑circuit​ applications. For closed‑loop travel/winch drives, use Rexroth A4VG (variable) or A2FM/A6VM (motors) with a charge pump. Attempting to use A4VSO in closed loop will result in overheating and rapid failure due to lack of case flushing and incorrect flow path.

Q6: What are the critical installation & commissioning steps?

A:

① Filtration​ — Maintain system cleanliness ≤ NAS 9 (ISO 4406 code 17/15/12). Install 10 µm or finer full‑flow return filter.

② Suction Line​ — Keep short (<1.5 m if possible), generously sized (≥ 1.25× pump inlet area), with 100–150 mesh suction strainer. Min. inlet pressure 0.8 bar abs — use a flooded suction if pump is above tank.

③ Alignment​ — Use a flexible coupling; the pump shaft must not​ carry radial or axial loads from the motor.

④ Bleeding​ — Crack open the case drain or highest bleeder to purge air before running. Manually rotate shaft 2–3 turns if accessible.

⑤ Initial Run​ — Start at low pressure/no load for a few minutes to verify quiet operation, correct rotation, and case drain flow, then gradually bring to working pressure.