The DB 20 series pressure relief valve is a pilot-operated hydraulic component designed for subplate mounting in accordance with ISO 5781 and DIN 24340 standards. Engineered to maintain constant system pressure by diverting excess flow to the tank, the DB 20 utilizes a two-stage design: a main stage consisting of a main spool and a pilot stage featuring a spring-loaded cone or ball. This configuration ensures stable pressure regulation across a wide flow range while minimizing pressure overshoot during transient load conditions. The valve’s performance is defined by its ability to maintain a flat pressure-flow characteristic curve, which is critical for preventing cavitation and hydraulic shock in high-pressure circuits.
For complete selection guidelines and cross-reference documentation on this product line, please consult our Rexroth equivalent hydraulic valves guide.
Technical Specifications and Performance Parameters
The following table summarizes the primary technical parameters for the DB 20 series, ensuring compatibility with standard industrial hydraulic power units.
| Parameter | Specification |
|---|---|
| Mounting Pattern | ISO 5781 / DIN 24340 |
| Max Operating Pressure | 350 bar (35 MPa) |
| Max Flow Rate | 300 L/min |
| Fluid Temperature Range | -20°C to +80°C |
| Viscosity Range | 10 to 800 mm²/s |
| Hysteresis | < 0.5% of max pressure |
Fluid Contamination and ISO 4406 Compliance
The longevity and operational precision of the DB 20 are strictly dependent on fluid cleanliness. Due to the tight tolerances between the main spool and the valve body, “spool silting” can occur if particulate matter enters the clearance gaps, leading to erratic pressure control or valve sticking. It is mandatory to maintain a fluid cleanliness level of at least 19/17/14 according to ISO 4406 standards. Filtration systems should be sized to prevent the ingress of contaminants during maintenance cycles or pump wear, as even minor silting in the pilot orifice can significantly alter the cracking pressure and response time of the valve.
Seal Elastomer Selection: NBR vs. FKM
The DB 20 is typically supplied with either Nitrile Butadiene Rubber (NBR) or Fluoroelastomer (FKM/Viton) seals. The selection of the seal material must align with the hydraulic fluid type and the operating temperature profile:
- NBR (Nitrile): Suitable for standard mineral-oil-based hydraulic fluids (HLP/HLPD) with operating temperatures up to 80°C. It offers excellent resistance to abrasion but is susceptible to degradation in the presence of certain synthetic fire-resistant fluids.
- FKM (Viton): Recommended for applications involving high-temperature cycles or when using synthetic fluids such as phosphate esters (HFD). FKM provides superior chemical resistance and maintains mechanical integrity at elevated temperatures, though it requires careful handling to avoid damage during installation.
Installation and Maintenance Considerations
To ensure compliance with ISO 1219 circuit symbols and optimal performance, the DB 20 must be mounted on a flat, rigid surface to prevent body distortion, which can cause internal leakage or spool binding. When adjusting the pressure setting, the lock nut must be torqued to the manufacturer’s specification to prevent drift caused by vibration. Periodic inspection of the pilot stage poppet-seat geometry is recommended; any evidence of erosion or pitting on the seat will result in internal leakage, preventing the valve from reaching its set pressure and causing excessive heat generation within the hydraulic circuit.