R900423213 ZDR6DA2-4X/210YM Direct acting pressure reducing valve, German original Rexroth

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.

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

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

• /210​ = spring stage, max. adjustable reduced pressure = 210 bar (medium stage; others: /75, /150, /315).

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

• 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; 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 side), 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.

Q6: What is the "M" seal version for?

M = FKM (Viton)​ seals — for:

• Higher fluid temperature (up to ~90 °C)

• Biodegradable oils (HEES, HETG — NBR not recommended)

• Some HFC applications (short-term; NBR preferred for prolonged HFC exposure)

  Not for phosphate ester (HFD) unless specially confirmed — standard NBR applies.

Q7: Common faults & causes?

• Reduced pressure too high / cannot lower:​ wrong spring stage, pilot orifice clogged, Y-drain line blocked (Y-version!), inlet pressure insufficient.

• Reduced pressure drifts / unstable:​ contaminated pilot seat, damaged sandwich-face O-ring causing internal leak, Y-line restricted or pinched.

• Excessive heating at T:​ Normal for 3-way ZDR — some bypass to T occurs to hold set pressure; excessive heat may indicate stuck spool from contamination — flush system & verify filtration (ISO 4406 18/16/13 or better).

Q8: Can one ZDR reduce both A- and B-side pressure?

Standard ZDR6 sandwich reduces pressure in one working line​ (usually marked A on sandwich face). For independent A+B reduction use two ZDR6 valves or a custom manifold.