R900424203 DBDS20K1X/400 Original German Rexroth overflow valve

FAQ - Frequently Asked Questions

Q1: What does the "/400" pressure code mean? Can I adjust it to 500 bar?

A:​ No.​ The "/400"​ indicates this valve is equipped with a specific spring for the 400 bar pressure stage. Although the valve body is rated for 630 bar, the spring in this model is designed for reliable adjustment only up to 400 bar. Attempting to set it to 500 bar will result in inaccurate pressure control and potential spring damage. For higher pressures, select a model with a /630 spring code.

Q2: What is the correct installation cavity size and torque?

A:​ This is an NG20​ size cartridge. You must use a standard DBD NG20 threaded cavity​ (commonly M45×1.5). The recommended tightening torque is typically 120–150 Nm, but you should confirm this in the technical data sheet to avoid damaging the threads or seals.

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

A:​ Backpressure is fully additive.​ Any pressure at the T-port directly adds to the pressure required to open the valve. For example, if the valve is set to 380 bar and the T-port has 20 bar of backpressure, the system will relieve at 400 bar. Ensure the total pressure (set pressure + T-port backpressure) does not exceed the valve's maximum rating of 630 bar.

Q4: Why is my valve chattering or not holding a stable pressure?

A:​ Common causes for chatter in direct-acting relief valves include:

1. Excessive Flow:​ Operating near or above the recommended 250 L/min flow limit for NG20.

2. High/Unstable Backpressure:​ Fluctuating pressure in the tank line disrupts the poppet's stability.

3. Contamination:​ Dirt or debris can cause the poppet to stick and release erratically. Ensure ISO 4406 20/18/15 cleanliness.

Q5: Is the standard NBR seal compatible with water glycol (HFC) or phosphate ester (HFD) fluid?

A:​ No.​ The standard R900424203 with NBR seals is not compatible​ with water glycol (HFC) or phosphate ester (HFD) fluids. For these applications, you must order a variant with FKM (Viton®) seals, which are typically denoted by a /V​ suffix in the model code (e.g., DBDS20K1X/400V).