R900483787 ZDR6DP2-4X/150YM Direct acting relief valve from Rexroth, Germany

FAQs for Rexroth ZDR6DP2-4X/150YM Pressure Reducing Valve

1. Q: This valve is rated for 150 bar secondary pressure. How is that different from the 75YM model?

   A:​ The primary difference is the maximum adjustable secondary pressure. The ZDR6DP2-4X/150YM​ can be set up to 150 bar, while the ZDR6DP2-4X/75YM​ is limited to 75 bar. The internal spring in the 150YM model is calibrated for a higher force range, allowing it to regulate a higher downstream pressure. The nominal size, flow capacity, and function are otherwise identical. Always select the model whose maximum rating meets or exceeds your required circuit pressure.

2. Q: How do I prevent the pressure setting from drifting over time due to vibration?

   A:​ The valve is equipped with an adjustment screw and a lock nut. After setting the desired pressure (using a gauge and under flow conditions), you must securely tighten the lock nut​ against the valve body. This mechanically locks the screw in place, preventing rotation from system vibration. It is a critical final step in the adjustment procedure. Periodically checking the setting during routine maintenance is also good practice.

3. Q: The downstream equipment is very sensitive to pressure spikes. Does this valve offer protection?

   A:​ Yes, it provides a key protective function. This valve includes an integral over-pressure relief path​ from the A port to the T port. If pressure in the secondary circuit (e.g., from an external force on a cylinder) tries to exceed the valve's set point, it will automatically open to allow flow to tank, thereby clamping the pressure at or near the set value. This protects sensitive downstream components from being over-pressurized.

4. Q: I need the valve to hold pressure in a circuit with zero flow for a long time. Is this suitable?

   A:​ It is functional but not ideal for zero-leakage applications. As a direct-acting valve, it has a characteristic internal leakage​ from P to T when regulating, which will cause the pressure to slowly decay if the downstream circuit is completely sealed and no makeup flow is supplied. For applications requiring long-term, zero-leakage pressure holding (like a locked clamp), a pilot-operated reducing valve or a circuit with an accumulator and check valve is more effective.

5. Q: The valve makes a whistling or hissing noise. What does this mean?

   A:​ A steady, high-frequency hissing sound typically indicates that the valve is actively throttling—meaning it is partially open and maintaining pressure by restricting flow from P to A while bypassing excess fluid to T. Some noise is normal during regulation, especially at high pressure drops. However, a loud, shrieking, or chattering noise could indicate cavitation​ (often due to a restricted inlet or excessive pressure drop) or instability, and should be investigated.