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# Poppet Valve

Hydraulic poppet valve

## Library

Flow Control Valves

## Description

The Poppet Valve block models a variable orifice created by a cylindrical sharp-edged stem and a conical seat.

The flow rate through the valve is proportional to the valve opening and to the pressure differential across the valve. The model accounts for the laminar and turbulent flow regimes by monitoring the Reynolds number (Re) and comparing its value with the critical Reynolds number (Recr). The flow rate is determined according to the following equations:

where

 q Flow rate p Pressure differential pA,pB Gauge pressures at the block terminals CD Flow discharge coefficient A(h) Instantaneous orifice passage area x0 Initial opening x Stem displacement from initial position h Valve opening hmax Maximum valve opening. The passage area remains constant and equal to Amax after this. ds Stem diameter α Cone angle ρ Fluid density DH Valve instantaneous hydraulic diameter ν Fluid kinematic viscosity Aleak Closed valve leakage area Amax Maximum valve open area

The block positive direction is from port A to port B. This means that the flow rate is positive if it flows from A to B and the pressure differential is determined as . Positive signal at the physical signal port S opens the valve.

## Basic Assumptions and Limitations

• Fluid inertia is not taken into account.

• The transition between laminar and turbulent regimes is assumed to be sharp and taking place exactly at Re=Recr.

• The flow passage area is assumed to be equal to the frustum side surface area.

## Dialog Box and Parameters

Valve stem diameter

The diameter of the valve stem. The default value is 0.01 m.

Seat cone angle

The angle of the valve conical seat. The parameter value must be in the range between 0 and 180 degrees. The default value is 120 degrees.

Initial opening

The initial opening of the valve. The parameter value must be nonnegative. The default value is 0.

Flow discharge coefficient

Semi-empirical parameter for valve capacity characterization. Its value depends on the geometrical properties of the orifice, and usually is provided in textbooks or manufacturer data sheets. The default value is 0.65.

Critical Reynolds number

The maximum Reynolds number for laminar flow. The transition from laminar to turbulent regime is supposed to take place when the Reynolds number reaches this value. The value of the parameter depends on orifice geometrical profile, and the recommendations on the parameter value can be found in hydraulic textbooks. The default value is 10.

Leakage area

The total area of possible leaks in the completely closed valve. The main purpose of the parameter is to maintain numerical integrity of the circuit by preventing a portion of the system from getting isolated after the valve is completely closed. An isolated or "hanging" part of the system could affect computational efficiency and even cause simulation to fail. Therefore, MathWorks recommends that you do not set this parameter to 0. The default value is 1e-12 m^2.

## Global Parameters

Parameters determined by the type of working fluid:

• Fluid density

• Fluid kinematic viscosity

Use the Hydraulic Fluid block or the Custom Hydraulic Fluid block to specify the fluid properties.

## Ports

The block has the following ports:

A

Hydraulic conserving port associated with the valve inlet.

B

Hydraulic conserving port associated with the valve outlet.

S

Physical signal port to control spool displacement.