What size hydraulic power unit do i need?

Selecting the correct size for a hydraulic power unit (HPU) requires balancing performance, durability, and cost.

1. Determine Peak System Pressure
Why: Dictates pump/valve pressure ratings and structural strength.
How: Identify the highest pressure any actuator (cylinder/motor) requires to move its load. Add 15–20% safety margin.
Critical Tip: If multiple actuators operate simultaneously, size for the combined peak demand – not individual averages.

2. Calculate Total Flow Demand
Why: Determines pump displacement and reservoir size.
How:
For cylinders: Flow = (Cylinder bore area × Stroke length) ÷ Time to complete stroke
For motors: Flow = (Motor displacement × RPM) ÷ Efficiency factor (~0.85)
Sum flows for concurrently operating actuators.
Red Flag: Ignoring flow regeneration (e.g., cylinder retracting faster due to rod displacement differences).

3. Assess Duty Cycle Severity
Why: Continuous operation needs oversizing to prevent overheating.
Key Questions:
Will the HPU run 30 sec/min? 10 min/hour? 24/7?
Are there frequent starts/stops?
Rule: Continuous duty = Select pump/motor 25% larger than theoretical flow/power.

4. Reservoir (Tank) Sizing
Minimum Capacity:
Industrial/mobile: ≥3× pump flow rate
High-duty cycle/hot environments: ≥5× pump flow rate
Critical Function: Allows air bubbles to escape, contaminants to settle, and heat dissipation.
Fail-Safe Check: Verify fluid level remains above pump inlet during all operating angles (mobile equipment).

5. Prime Mover (Motor/Engine) Power
Formula: HP = (GPM × PSI) ÷ (1714 × Efficiency)
Efficiency: Gear pump = 0.85, Piston pump = 0.92
Example: 10 GPM at 2500 PSI with piston pump → (10 × 2500) ÷ (1714 × 0.92) ≈ 15.8 HP → Round up to 20 HP motor.
Torque Check: Engine-driven units must deliver peak torque at operating RPM.

6. Heat Dissipation Capacity
High-Temp Risk: Fluid degrades above 180°F (82°C).
Solutions:
Air-cooled: Add finned reservoirs or fan-coolers if ambient < 95°F (35°C). Water-cooled: Mandatory for high-power continuous systems.
Warning Light: Oil darkening rapidly = undersized cooling.

7. Control Valve Flow Matching
Sizing Principle: Valve port flow rating must exceed actual system flow.
Consequence: Undersized valves create pressure drops → heat generation → failure.
Pro Tip: For proportional valves, ensure rated flow aligns with controlled actuator speed – not just max pump flow.

8. Environmental Derating
High Altitude: Electric motors lose power; engines need turbocharging.
Hot Climates: Fluid thins – increase reservoir size or add coolers.
Dusty Sites: Oversize filters or use pressurized reservoir caps.

9. Future-Proofing
Add 25% reserve flow/pressure if:
System modifications are planned
Loads may increase
New actuators could be added