R900423731 DBDS6P1X/400 Rexroth Germany made overflow valve

Q1: Is this a pilot-operated or direct-acting relief valve?

It is a direct-acting seat valve (DBD series)​ — no pilot stage. The spring-loaded poppet/ball opens immediately when system pressure exceeds the set spring force.

Q2: What does "P1X / 400" mean?

• P1​ = adjustment type: hexagon socket with protective cap (Allen key adjustable).

• 1X​ = component series index (interchangeable within series 1X).

• /400​ = spring pressure stage, maximum settable relief pressure = 400 bar.

Q3: How do I adjust the relief pressure?

Depressurize the system, remove the protective cap, turn the internal setscrew with an Allen key — clockwise to increase, counterclockwise to decrease. Reinstall the cap and verify with a pressure gauge at the P-port. Factory preset is typically near the low end of the spring range; always adjust on-site to the required system pressure.

Q4: Which subplate is required?

Use a standard NG6 (Size 6) subplate​ per ISO 6264 with P and T ports (commonly G 1/4" or M14×1.5 threaded ports on the subplate). The valve mounts flush to the subplate via four M5 bolts (tightening torque approx. 8–10 N·m — refer to Rexroth mounting drawing).

Q5: Does T-port backpressure affect the set pressure?

Yes. The spring chamber drains internally to the T-port, so any backpressure at T adds 1:1 to the relief/cracking pressure. Keep T-line backpressure minimal or compensate in the setpoint.

Q6: Common fault symptoms?

• Pressure won't reach set value:​ wrong spring grade (not /400), high T-backpressure, poppet sticking due to contaminated oil, or pump issue.

• Continuous dribble / external leak:​ damaged seating surface, worn O-ring, or contamination trapped in the seat — clean or replace.

• Chatter / noise:​ air in the system, flow exceeding 50 L/min, or excessive line resonance — bleed air and confirm flow rating.

Q7: Fluid & seal compatibility?

Standard NBR seals suit mineral oil (HL/HLP) and HFC (water-glycol). For HEES/HETG biodegradable oils or HFD phosphate ester, FKM (Viton) seals are required — order the "V" seal variant if needed.