R900445958 ZDR6DA2-4X/150YM Rexroth pressure reducing valve made in Germany

Frequently Asked Questions (FAQ)

Q1: Is ZDR a relief 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 primary (inlet) pressure drops below the set reduced pressure, the ZDR opens fully and passes flow unregulated.

Q2: What does "DA2 /150YM" mean?

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

• /150​ = spring stage, max. adjustable reduced pressure = 150 bar (low-pressure stage; other stages: /75, /210, /315).

• Y​ = external pilot drain — pilot oil returns via separate Y-port to tank.

• M​ = FKM (Viton) seal material.

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.

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), A (or B) = reduced secondary pressure to actuator, T = tank return, Y = external pilot drain to tank (must be connected!).

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

If the T-line in the valve stack has >2–3 bar backpressure, an internally drained ZDR's set pressure will increase by the amount of T-backpressure. The Y-version​ isolates the pilot from T, keeping the set reduced pressure stable. Always plumb Y separately to tank if T-backpressure exists.