R900593530 DB20-2-5X/315 Rexroth Germany made overflow valve

Q1: Is DB20-2-5X/315 direct-acting or pilot-operated?

It is a pilot-operated (two-stage) relief valve. The pilot valve controls pressure over the main stage spool, giving better pressure stability and lower pressure override at high flow vs. a direct-acting valve of the same size.

Q2: What does "2 - 5X / 315" mean?

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

• 5X​ = component series index 5X (dimensions fixed within series 50–59).

• /315​ = pressure stage, maximum adjustable relief pressure = 315 bar (adjustable roughly 4–315 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 range; always adjust on-site.

Q4: Which subplate is required?

Use a standard NG20 (Size 20) subplate​ per ISO 6264 with P and T ports. The valve mounts via four M12 bolts (tightening torque approx. 70–80 N·m). Subplate port threads are commonly G 3/4" BSP or M27×2. Optional ports X (remote pressure control) and Y (external pilot drain) are on the valve body.

Q5: Internal vs. external pilot drain — does T-backpressure matter?

This model has internal pilot drain​ — pilot oil returns via the T-port. Any significant backpressure at T will add to the set pressure. If your T-line has >5 bar backpressure, consider the DB…Y version (external pilot drain to a separate tank line) to avoid pressure shift.

Q6: Common fault symptoms & causes?

• Pressure won't reach set value / unstable:​ contaminated pilot orifice/nozzle, wrong pressure stage, excessive T-backpressure (internal drain), broken pilot spring.

• Slow response / pressure creep:​ clogged pilot nozzle, air in pilot circuit.

• External seepage:​ damaged O-ring on mounting face or subplate not flat — check subplate surface and torque.

• Chatter:​ air in system, long flexible pilot lines if remotely connected, or flow near Qmax — bleed air and verify correct subplate.

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.