R900410875 ZDR10DP2-5X/75YM Rexroth Germany made pressure reducing valve

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 protect the pump from overpressure.

Q2: What does "DP2 /75YM" mean?

• DP2​ = NG10 sandwich, rotary hand knob with protective cap (hand-adjustable).

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

• Y​ = external pilot drain — pilot oil returns via separate Y-port to tank, not via the 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 NG10 subplate. Uses NG10 DIN 24340 Form E / ISO 5781 bolt pattern (four M10 bolts). 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 separately!).

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.

Q7: Common faults & causes?

• Reduced pressure too high / cannot lower:​ wrong spring stage (e.g. /210 or /315 installed), pilot orifice clogged, Y-drain line blocked (Y-version!), inlet pressure insufficient to allow regulation.

• Reduced pressure drifts / unstable:​ contaminated pilot seat, damaged O-ring on sandwich face 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).