KEVOS® MAKEOS · Hydraulics
Hydraulic Orifice Restrictor Design (Drill Size, Flow, Heat)
What orifice size gives the flow I want at this pressure drop, what flow does the nearest drill size actually give, and how much heat does the restrictor put into the oil?
Design of a fixed orifice to limit flow in a hydraulic or lubrication circuit: exact orifice diameter for the target flow at the pressure drop, the diameter rounded to your drill steps or one you choose, the flow it gives and the pressure drop it needs for the target flow (as the orifice flow tool), jet velocity, the power turned to heat and the temperature rise of the oil passing through, checked against your flow tolerance, least orifice size for clogging and temperature rise limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Flow wanted | L/min | Flow you want through the restrictor. |
| Pressure drop available | bar | Pressure difference across the restrictor. |
| Discharge coefficient | Discharge coefficient of the orifice (about 0.6–0.7 for a sharp-edged orifice). | |
| Fluid density | kg/m³ | Density of the fluid. |
| Fluid specific heat | kJ/kg·K | Specific heat of the fluid (mineral oil about 1.9 kJ/kg·K). |
| Drill size step | mm | Steps between available drill sizes. |
| Orifice diameter chosen (0 = rounded) | mm | Orifice diameter you intend to use; 0 rounds the exact size to the drill step. |
| Limits | ||
| Flow tolerance | % | How far the flow may differ from the target. |
| Least orifice diameter (clogging) | mm | Smallest orifice you accept with your filtration. |
| Largest oil temperature rise | K | Largest temperature rise of the fluid passing through. |
Method and formulas
- Q = C_d A √(2Δp ÷ ρ), so d = √[4Q ÷ (π C_d √(2Δp ÷ ρ))] (as the orifice flow tool).
- Chosen d rounded to the drill step; flow at the chosen d and Δp needed for the target flow.
- Heat = Δp × Q; temperature rise = Δp ÷ (ρ c_p).
- Example: 4 L/min at 70 bar needs 1.0389 mm; a 1 mm hole gives 3.7063 L/min and heats the oil 4.2798 K.
Limitations
- Turbulent flow through a sharp-edged orifice; at low Reynolds numbers C_d falls.
- Cavitation and flow forces are not checked.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a restrictor for a lubrication point or pilot line
- Limit cylinder speed with a fixed orifice
- Check heat from throttling
Who it is for
- Hydraulic engineers
- Machine designers
- Maintenance technicians
What you get
- Exact and chosen orifice diameter
- Flow at the chosen size and pressure drop for the target
- Jet velocity, heat and temperature rise
Interpreting the result
- Flow changes with the square of the diameter: a 0.1 mm step on a 1 mm hole is about 20% in flow.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027, 352–368. Topic reference; no source tables or recommended settings are reproduced.
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Open the Hydraulic Orifice Restrictor Design (Drill Size, Flow, Heat) calculator
