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

No. A relief valve (DB/DBD) limits upstream/system pressure; a pressure reducing valve (ZDR) maintains a lower, constant pressure in a downstream (secondary) circuit. If inlet (primary) pressure drops below the set reduced pressure, the ZDR opens fully and passes flow unregulated.

• 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

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.

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).

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.

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.

• 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)

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.