R901019399 DBW20A1-5X/350-6EG24N9K4 Electromagnetic overflow valve original German Rexroth

Frequently Asked Questions (FAQ)

Q1: What is the difference between DB and DBW?

DB is a pilot relief valve only — limits system pressure. DBW adds an integrated directional solenoid valve: when energized the main stage is unloaded (P→T open, near 0 bar); when de-energized it works as a normal relief valve at the set pressure.

Q2: How is Size 20 (NG20) different from Size 10 (NG10)?

• Flow:​ NG20 handles approx. 500 L/min vs ~250 L/min for NG10.

• Mounting:​ NG20 uses four M12 bolts (~70–80 N·m) on an NG20 subplate (G 3/4" or M27×2 ports); NG10 uses M10 bolts on NG10 subplate.

• Pressure stages & solenoid specs are identical.

Q3: How do I adjust the relief pressure?

With system depressurized, remove the protective cap, turn the setscrew with an Allen key — clockwise to increase, counterclockwise to decrease. Factory preset is typically near minimum of the spring range. Reinstall cap and verify with a pressure gauge. The solenoid does NOT change the set pressure.

Q4: What is the solenoid logic?

Standard: Solenoid DE-energized = relief active​ at set pressure. Solenoid ENERGIZED = system unloaded​ (P connected to T). Confirm this matches your control logic before wiring.

Q5: Which subplate and electrical connector are needed?

• Subplate: standard NG20 (ISO 6264)​ with P and T ports (G 3/4" BSP or M27×2 on subplate), four M12 bolts @ ~70–80 N·m.

• Electrical: EN 175301-803 Form A (DIN 43650-A) 3-pin + PE connector, 24 V DC. If the plug has LED indication, observe (+) / (–) polarity markings.

Q6: Common faults & causes?

• Solenoid clicks but system does NOT unload:​ pilot orifice clogged, main spool stuck, no coil current (check ~18–28 Ω), manual override jammed.

• Pressure won't reach set value / creeps early:​ wrong spring (not /350), pilot damping hole blocked, contaminated pilot seat, excessive T-backpressure (internal pilot drain).

• Coil overheats / burnt smell:​ overvoltage (>10% above 24V), wrong voltage coil fitted — replace only with correct G24 wet-pin coil.

• Chatter / unstable:​ air in system, high T-backpressure, worn pilot seat — bleed air first.

Q7: Does T-port backpressure affect set pressure?

Yes — this model has internal pilot drain. Backpressure at T adds 1:1 to the relief setpoint. If your tank line has >5 bar sustained backpressure, consider the DBW…Y version (external pilot drain to separate tank line).

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.