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MapleSim Hydraulics Library from Modelon

Counter Balance  Counterbalance valve

The Counter Balance component describes a counterbalance valve. The counterbalance valve is a pressure control device and allows (almost) free flow from port A (inlet) to port B (load). It blocks reverse flow unless a pilot pressure is sensed at port C (pilot) or load pressure exceeds relief setting. This valve ensures that the actuator always sees a positive load pressure, even under overrunning load situations.

Backpressure at port A does affect the valve setting unless an atmospherically vented counterbalance valve is used where the spring chamber is atmospherically referenced.

The behavior of the valve is modeled as an orifice whose diameter depends on the pressures at the three ports.

Pressures

Flows

port_B&period;p<pPreload and port_A&period;p&equals;0 and port_C&period;p&equals;0

Leakage flow from B  A (given by GLeak). This is the load holding function.

pPreload<port_B&period;p < pFull and port_A&period;p&equals;0 and port_C&period;p&equals;0

Flow from B  A. Valve is partially open. This is the pressure relief function.

pFull<port_B&period;p and port_A&period;p&equals;0 and port_C&period;p&equals;0

Flow from B  A. Valve is completely open. Flow rate is determined by qnom and &Delta;pnom.

port_C&period;p<pPreloadpressureRatio and port_B&period;p&equals;0 and port_A&period;p&equals;0

Leakage flow from B  A (given by GLeak).

pPreloadpressureRatio<port_C&period;p < pFullpressureRatio and port_B&period;p&equals;0 and port_A&period;p&equals;0

Flow from B to A. Valve is partially open.

pFullpressueRatio<port_C&period;p and port_B&period;p&equals;0 and port_A&period;p&equals;0

Flow from B  A. Valve is completely open. Flow rate is determined by qnom and &Delta;pnom. This is the normal operation when the valve is opened by the pressure at the pilot.

port_A&period;p<pCheckValvePreload and port_B&period;p&equals;0 and port_C&period;p&equals;0

Leakage flow from B  A (given by GLeak).

pCheckValvePreload<port_A&period;p and port_B&period;p&equals;0 and port_C&period;p&equals;0

Flow from A  B through the check valve, given by qnomCheckValve and &Delta;pnom.

pPreload<port_B&period;pport_A&period;pbackpressureRatio&plus;port_C&period;ppressureRatio and port_B&period;pport_A&period;pbackpressureRatio&plus;port_C&period;ppressureRatio<pFull

Flow from B  A. Valve is partially open.

pFull<port_B&period;pport_A&period;pbackpressureRatio&plus;port_C&period;ppressureRatio

Flow from B  A. Valve is completely open. Flow rate is determined by qnom and &Delta;pnom. This is the normal operation when the valve is opened by the pressure at the pilot.

 

Setting parameters:

pPreload

Load pressure to start opening valve. Some manufacturers call this value the thermal relief pressure which is approximately 60e5 Pa above their holding pressure of counterbalance setting.

pFull

Load pressure to open valve completely. Typically not specified; depends on the spring characteristics and is responsible for the opening characteristic.

pressureRatio

Pressure ratio (that is, the multiplier for pilot pressure).

backpressureRatio

Pressure ratio (that is, the  multiplier for back pressure at port 2). It is zero for atmospherically vented valves and around 1.0 for others.

pCheckValvePreload

Pressure to open check valve completely.

qnom

Nominal flow rate at dpnom of load holding valve (that is, the poppet).

&Delta;pnom

Pressure drop at qnom.

qnomCheckValve

Nominal flow rate of check valve at &Delta;pnom.

GLeak

Conductance of leakage. Very small value.

 

The mass and flow forces are not included. Use the modifier(s)

Volume1(port_B(p(start=1e5,fixed=true)))

and/or

Volume2(port_A(p(start=1e5,fixed=true)))

to set the initial condition(s) for the pressure of the lumped volume(s) Pa.

The flow rate at the pilot port 3 is equal to zero. This pressure at this port is not modeled as a state.

Other names for this valve include motion control valve and over center valve.

Related Components

Name

Description

Check Valve Two

Spring-loaded check valve with laminar/turbulent flow; gives the characteristic of the flow from port 2 to 1. This model is also used to model the linearly pressure dependent leakage with GLeak.

 

Equations

Variables

Connections

Parameters

Equations

ν&equals;Modelica.Media.Air.MoistAir.Utilities.spliceFunctionx&equals;&Delta;p&comma;pos&equals;νoilp&equals;pAabs&comma;T&equals;T&comma;vair&equals;vgasoil&comma;psat&equals;psat&comma;neg&equals;νoilp&equals;pBabs&comma;T&equals;T&comma;vair&equals;vgasoil&comma;psat&equals;psat&comma;&Delta;x&equals;100

ρ&equals;Modelica.Media.Air.MoistAir.Utilities.spliceFunctionx&equals;&Delta;p&comma;pos&equals;ρoilp&equals;pAabs&comma;T&equals;T&comma;vair&equals;vgasoil&comma;psat&equals;psat&comma;neg&equals;ρoilp&equals;pBabs&comma;T&equals;T&comma;vair&equals;vgasoil&comma;psat&equals;psat&comma;&Delta;x&equals;100

T&equals;T0oil&plus;&Delta;Tsystem

q&equals;mflowAρ

&Delta;p&equals;pAlimitedpBlimited

pAabs&equals;pA&plus;patmoil

pAlimited&equals;maxpA&comma;pvapouroilpatmoil

pBabs&equals;pB&plus;patmoil

pBlimited&equals;maxpB&comma;pvapouroilpatmoil

Variables

Name

Value

Units

Description

Modelica ID

&Delta;p

 

Pa

Pressure drop

dp

q

 

m3s

Flow rate flowing into port_A

q

pAlimited

 

Pa

Limited gauge pressure

pA_limited

pBlimited

 

Pa

Limited gauge pressure

pB_limited

ρ

 

kgm3

Upstream density

rho

ν

 

m2s

Upstream kinematic viscosity

nu

pAabs

 

Pa

Absolute pressure pA

pA_abs

pBabs

 

Pa

Absolute pressure pB

pB_abs

T

 

K

Local temperature

T

pAsummary

pA

Pa

Pressure at port A

summary_pA

pBsummary

pB

Pa

Pressure at port B

summary_pB

&Delta;psummary

&Delta;p

Pa

Pressure drop

summary_dp

qsummary

q

m3s

Flow rate flowing into port_A

summary_q

Phydsummary

&Delta;pq

W

Hydraulic Power

summary_HP

psat

[1]

Pa

Gas saturation pressure

p_sat

VA

 

 

 

VolumeA

VB

 

 

 

VolumeB

CheckValve

 

 

 

CheckValve

Poppet

 

 

 

Poppet

counterBalanceBaseBlock

 

 

 

counterBalanceBaseBlock

[1] oil.gasSaturationPressureT&equals;T&comma;vgas&equals;oil.vgas

Connections

Name

Description

Modelica ID

portA

Layout of port where oil flows into an element (0<mflow, pB<pA means 0<&Delta;p)

port_A

portB

Hydraulic port where oil leaves the component (mflow<0, pB<pA means 0<&Delta;p)

port_B

oil

 

oil

portC

Port where typically the control pressure for the pilot is connected

port_C

Parameters

General Parameters

Name

Default

Units

Description

Modelica ID

&Delta;Tsystem

0

K

Temperature offset from system temperature

dT_system

use volume A

true

 

If true, a volume is present at port_A

useVolumeA

use volume B

true

 

If true, a volume is present at port_B

useVolumeB

VA

10-6

m3

Geometric volume at port A

volumeA

VB

10-6

m3

Geometric volume at port B

volumeB

ppreload

1.25·107

Pa

Load pressure to start opening valve

pPreload

pFull

65ppreload

Pa

Load pressure to open valve completely

pFull

pressureRatio

5

 

Pressure ratio, i.e. multiplier for pilot pressure to open valve

pressureRatio

backpressure ratio

pressureRatio

 

Pressure ratio, i.e. multiplier for back pressure at port 2 to open valve; 0 for atmospherically vented valve

backpressureRatio

pCheckValvePreload

1.25·105

Pa

Pressure to open check valve completely

pCheckValvePreload

Gleak

10-15

m3sPa

Conductance of leakage

GLeak

Flow Parameters

Name

Default

Units

Description

Modelica ID

qnom

0.001

m3s

Nominal flow rate at dpnom of load holding valve

qnom

&Delta;pnom

2.2·106

Pa

Pressure drop at qnom

dpnom

qnomCV

qnom

m3s

Nominal flow rate at dpnom of check valve

qnomCheckValve

k1

10

 

Laminar part of orifice model

k1

k2

2

 

Turbulent part of orifice model, k2&equals;1Cd2

k2

See Also

Check Valve Two

Valves

MapleSim Hydraulics Library from Modelon Overview

 


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