R900410849 ZDR6DA2-4X/150Y German Rexroth direct acting pressure reducing valve

Frequently Asked Questions (FAQ)

Q1: Is ZDR a pressure 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 regardless of higher primary pressure (within its range). If primary pressure drops below the set reduced pressure, the ZDR opens fully and does not regulate.

Q2: What does "DA2" and "/150Y" mean?

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

• /150​ = spring pressure stage, maximum adjustable reduced pressure = 150 bar (this is the low-pressure stage; other stages are /75, /210, /315).

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

Q3: How do I adjust the reduced pressure?

With the secondary circuit pressurized, lift/remove the cap and turn the rotary knob clockwise to increase​ the reduced pressure, counterclockwise to decrease. Read the actual secondary pressure with a gauge — the knob has no scale. The factory preset is typically near minimum; always adjust under flow conditions if possible for accurate reading.

Q4: How is the ZDR mounted?

As a sandwich (stackable) valve​ between the directional control valve and the NG6 subplate (or between two sandwiches). It uses the same bolt pattern as NG6 DIN 24 340 Form E / ISO 5781. Port designation on sandwich: P=primary (high), A(or B)=reduced secondary, T=tank, Y=drain to tank.

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

If the T-line (tank line in the stack) has >2–3 bar backpressure, an internally drained​ ZDR's set reduced pressure will be affected (increased by T-backpressure). The Y-version​ drains the pilot independently to tank, isolating the set pressure from T-backpressure. Use Y-version whenever T-backpressure is present.

Q6: Common faults & causes?

• Reduced pressure too high / cannot be lowered:​ wrong spring (not /150 — e.g. /315 installed), pilot orifice clogged, knob not turned fully CCW, or upstream pressure too low to allow regulation.

• Reduced pressure too low / fluctuates:​ contaminated pilot seat, damaged O-ring on sandwich face allowing internal leakage, Y-drain line blocked (Y-version), or insufficient upstream pressure.

• Excessive heat / continuous flow to T:​ Normal in 3-way ZDR — some bypass to T occurs to hold reduced pressure; excessive heating may indicate incorrectly sized valve or stuck spool — check for contamination.

Q7: Can it be used for both A- and B-side pressure reduction?

The standard ZDR6 sandwich reduces pressure in one working line​ (typically port A of the sandwich stack). For dual-pressure reduction (A+B independently), use two ZDR6 valves or a ZDR10 in a custom manifold. Check port marking on the sandwich face (P→A reduced, T, Y).

Q8: Fluid & seal compatibility?

NBR seals = mineral oil (HL/HLP) & HFC (water-glycol). For HEES/HETG biodegradable oils or HFD phosphate ester → specify FKM (Viton) seal variant. Maintain oil cleanliness per ISO 4406 code 18/16/13 or better.