R900410855 ZDR6DA2-4X/210Y Pressure valve from Rexroth, Germany

Frequently Asked Questions (FAQ)

Q1: Is ZDR a relief valve / overflow valve?

No. A relief valve (DB/DBD)​ limits upstream/system pressure; a pressure reducing valve (ZDR)​ maintains a lower, constantpressure in a downstream (secondary) circuit. If inlet (primary) pressure drops below the set reduced pressure, the ZDR opens fully and passes flow unregulated — it does not limit pump pressure.

Q2: What does "DA2 /210Y" mean?

• DA2​ = NG6 sandwich, rotary hand knob with protective cap (hand‑adjustable).

• /210​ = spring stage, max. adjustable reduced pressure = 210 bar (medium stage; /75 low, /150 low‑med, /315 high).

• Y​ = external pilot drain — pilot oil returns via separate Y‑port to tank, not via the sandwich T‑channel.

Q3: How do I adjust the reduced pressure?

With the secondary circuit under flow, lift/remove the cap and turn the rotary knob clockwise to increase, counterclockwise to decrease. Verify with a pressure gauge at the secondary port — the knob has no calibrated scale. Factory preset is typically near minimum; always fine‑tune under operating flow if possible.

Q4: How is the valve mounted?

As a sandwich (stackable) valve​ between a directional control valve and the NG6 subplate. Uses NG6 DIN 24340 Form E / ISO 5781 bolt pattern. Sandwich port IDs: P = primary (high pressure from pump / P‑port of subplate), A (or B) = reduced secondary pressure to actuator, T = tank return, Y = external pilot drain to tank (must be plumbed!).

Q5: Why specify the "Y" (external drain) version?

If the T‑line in the valve stack has >2–3 bar backpressure, an internally drained ZDR's set reduced pressure will increase by the amount of T‑backpressure. The Y‑version​ drains the pilot independently to tank, keeping the set reduced pressure stable. Always use Y‑version if T‑backpressure is present or uncertain.