A valve can fit the mounting pattern and still create excessive pressure loss or heat. Flow rating, spool path, fluid viscosity and duty cycle must be considered together.
Send the original reference: Include the complete model code, quantity, destination and available photos or drawings.
Pressure loss becomes heat
Approximate hydraulic power converted to heat is P (kW) = pressure drop (bar) × flow (L/min) ÷ 600. A 12 bar pressure drop at 80 L/min represents about 1.6 kW of heat while that flow path is active.
Why catalog flow is not a universal limit
| Factor | Effect on pressure drop or operation | What to compare |
|---|---|---|
| Spool path | Different metering paths have different losses | Curve for the actual spool and flow path |
| Flow rate | Loss normally increases rapidly as flow rises | Expected continuous and peak flow |
| Viscosity and temperature | Cold or high-viscosity fluid changes losses and response | Fluid grade and temperature range |
| Return or tank pressure | Can affect seals, actuator behavior and pilot functions | Permissible port pressure |
| Duty cycle | Determines average heat generation | Time at each flow and pressure condition |
Directional-valve comparison checklist
- Mounting standard and nominal size
- Exact spool symbol and center condition
- P-to-A, P-to-B, A-to-T and B-to-T flow paths
- Pressure-drop curves at relevant viscosity
- Working, peak and tank-port pressure limits
- Internal and external leakage expectations
- Solenoid voltage, power, duty and connector
Warning signs after a replacement
- Unexpected oil-temperature rise
- Slower cylinder or motor speed
- Higher upstream pressure for the same load
- Unstable motion or increased shock
- Coil overheating or incomplete shifting
- Noise across a throttled flow path
Data required for a safer quotation
- Complete original code and spool symbol
- System flow and working pressure
- Fluid and temperature range
- Cycle timing and time in neutral
- Expected tank pressure
- Available cooling capacity when heat is already a concern