## Hydraulic orifice definition

- @HYDRAULIC_ORIFICE_DEFINITION {
- @HYDRAULIC_ORIFICE_NAME {HydOrfcName} {
- @HYDRAULIC_DEVICE_MODEL_NAME {HydModl}
- @HYDRAULIC_CHAMBER_NAME {HydChmb0Name, HydChmb1Name}
- @FUNCTION_1D_NAME {Fun1DName}
- @ORIFICE_ENTRANCE_PRESSURE {p
_{Ent}} - @ORIFICE_CIRCUIT_PRESSURE {p
_{Cir}} - @COMMENTS {CommentText}
- }
- }

### Introduction

Figure 1. Configuration of the hydraulic orifice.

The **hydraulic orifice**, shown in fig. 1, allows the flow of hydraulic fluid through an orifice of sectional area * A_{orf}* and is associated with hydraulic device model,

**. The orifice is connected to two hydraulic chambers,**

*HydModl***and**

*HydChmb0Name***, respectively, with pressures**

*HydChmb1Name**and*

**p**_{0}*, respectively. A pressure differential,*

**p**_{1}*, will drive a flow rate*

**Δp = p**_{0}- p_{1}*across the orifice; the positive direction of this flow is indicated on the figure.*

**Q**_{orf}Pressures * p_{0}* and

*are, in general, the pressures in chambers*

**p**_{1}**and**

*HydChmb0Name***, respectively. For the linear hydraulic actuator, the orifice connects a chamber to an oil supply that can be at the entrance pressure**

*HydChmb1Name**or at the circuit pressure*

**p**_{Ent}*.*

**p**_{Cir}The description and formulation of the hydraulic orifice and elements describes the relationships among these variables.

### Computation of the orifice flow

The flow through the orifice, * Q_{orf}*, is related to the pressure drop,

*, across the orifice by means of 1D function,*

**Δp****. The following formula is used,**

*Fun1DName**,*

**Q**_{orf}= F(|Δp|) sign(Δp)where a 1D function,

*, defines the relationship between the flow and the pressure drop across the orifice through a Chebyshev expansion. The term*

**F = F(|Δp|)***enforces the sign convention.*

**sign(Δp)**Typically, the flow-pressure drop relationship is determined experimentally and a Chebyshev approximation is used to fit the data. In the absence of experimental data, the following formula can be used

**Q _{orf} = A_{orf} C_{d}√(2|Δp|/ρ) sign(Δp),**

where

*is the orifice throttling area and ρ the mass density of the hydraulic fluid. For turbulent flow conditions, the theoretical value of the discharge coefficient is*

**A**_{orf}*. This empirical formula corresponds to a Chebyshev expansion with a single term,*

**C**_{d}= 0.611*.*

**c**_{1}= A_{orf}C_{d}√(2/ρ)### NOTES

- It is possible to attach comments to the definition of the object; these comments have no effect on its definition.