R900907684 DBW20B2-5X/315-6EG24N9K4 Electromagnetic overflow valve manufactured by Rexroth in Germany

Frequently Asked Questions (FAQ)

Q1: What is the difference between A-version and B-version (DBW20A2 vs DBW20B2)?

Both are pilot-operated relief valves with solenoid unload and identical pressure/flow/solenoid specs. The B-version has a different pilot damping orifice​ which changes dynamic response (pressure overshoot, settling time). A-version is the general-purpose default; B-version is selected when system-specific stability tuning is needed. Externally both A2 and B2 have the same rotary hand knob adjustment.

Q2: Is this direct-acting or pilot-operated?

It is a pilot-operated (two-stage) relief valve with solenoid unloading. A pilot stage controls the main spool for stable high-flow relief; the integrated solenoid can command the valve to dump system pressure to tank.

Q3: How do I adjust the relief pressure?

With system depressurized, lift/remove the protective cap and turn the rotary knob clockwise to increase, counterclockwise to decrease. Factory preset is typically near minimum of the spring range. Replace the cap after setting and verify with a pressure gauge. The solenoid does NOT alter 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, near tank pressure). 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 /315), 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.