FAQ:

1. What is DFR control, and how does it work?

DFR​ is a combined pressure-flow control​ with load sensing (LS).

• Pressure Control: Limits system pressure to a set maximum (like a relief valve).

• Flow Control (LS): The pump automatically adjusts its swashplate angle to deliver only the flow required by the actuators, maintaining a constant pressure differential (Δp) across the control orifice. This results in significant energy savings​ compared to constant flow pumps.

2. Can I mount an additional pump on the back?

No.​ The code N00​ in VPA12N00​ explicitly indicates no through-drive. The shaft does not extend through the rear cover, so you cannot​ mount a second pump (gear or piston) on the back of this unit. If you need a tandem pump configuration, you must order a variant with a through-drive code (e.g., ending in K...).

3. What are the critical installation precautions?

• Case Drain (L ports): This pump has two case drain ports. They must be connected separately to tank​ with minimal backpressure (max 2–3 bar). Do not tee them into the main return line. This is critical for flushing heat and preventing seal/bearing failure.

• Suction Conditions: Ensure inlet pressure at port S is ≥ -0.8 bar​ (absolute) to avoid cavitation. Use short, large-diameter suction lines.

• Rotation: Confirm motor rotation matches the pump's "R" (clockwise) designation. Running backwards can destroy the pump.

4. Why is my pump noisy or overheating?

• Noise: Usually caused by cavitation. Check suction filter, inlet line for leaks, or oil viscosity being too high at startup.

• Overheating: Often due to excessive case pressure​ (blocked or undersized case drain line) or operating for long periods at high pressure with small displacement (high power loss).

5. How do I adjust the pressure and flow settings?

The DFR control has two adjustment screws (usually under caps on the control housing):

1. Pressure Limiter: Sets the maximum system pressure (clockwise to increase).

2. Flow Controller (LS Δp): Sets the pressure differential for load sensing (typically set to 10-20 bar).

Always adjust under controlled conditions with a pressure gauge.

6. Is an external relief valve still needed?

Yes.​ While the DFR control limits pressure, it is not a safety valve. You must install a separate system relief valve​ (e.g., a DB/DBW type) in the main line as a safety backup against control failure.

7. What is the difference between DFR and DRS?

• DFR: Typically used in industrial applications with explicit pressure/flow control.

• DRS: Often used in mobile applications with a stronger emphasis on load sensing. The functional principle is very similar, but the control response and internal pilot circuitry may differ.

Disclaimer:​ For precise installation and commissioning, always refer to the official Rexroth technical data sheet RE 25700​ for A10VSO Series 31 pumps.