R900423726 DBDS6K1X/400 Rexroth Germany plug-in overflow valve

FAQ - Frequently Asked Questions

Q1: What is the key difference between the /400 and the /100 or /200 models?

A:​ The /400​ suffix indicates this valve is equipped with a heavy-duty spring calibrated for a maximum setting of 400 bar. The /100 and /200 models have softer springs and cannot be adjusted to 400 bar. While the valve body rating is 400 bar, you must use the correct spring version (/400) to achieve reliable pressure settings in the 315–400 bar range.

Q2: What is the correct installation cavity and torque?

A:​ You must use a standard DBD NG6 (M28×1.5) threaded cavity. Using an incorrect cavity will cause leakage or malfunction. The recommended tightening torque is 50±5 Nm. Over-tightening can damage the threads or seals, while under-tightening will cause leaks.

Q3: How does backpressure on the T (tank) port affect the set pressure?

A:​ Backpressure is fully additive.​ Any pressure at the T-port is directly added to the pressure required to open the valve. For example, if the valve is set to 350 bar and the T-port has 30 bar of backpressure, the system will relieve at approximately 380 bar. Ensure the total pressure (set pressure + backpressure) does not exceed the valve's 400 bar maximum rating.

Q4: Why is the valve chattering or oscillating near the set pressure?

A:​ Chatter is common with direct-acting valves at high pressures and flows. Primary causes are:

1. Excessive Flow:​ The NG6 size is optimized for flows up to 50 L/min. If your flow is higher, consider an NG10 valve.

2. High Tank Backpressure:​ Unstable or high backpressure disrupts the poppet's stability.

3. Contamination:​ Dirt can cause the poppet to stick and then release erratically.

Q5: Can I use this valve with phosphate ester (HFD) fluid?

A:​ No, not with the standard version.​ The standard R900423726 has NBR seals, which are not compatible​ with phosphate ester (HFD) fluids. For HFD fluids, you must order a variant with FKM (Viton®) seals, which typically have a /V​ suffix (e.g., DBDS6K1X/400V).