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 $\mathrm{port_B}.p<\mathrm{pPreload}$ and $\mathrm{port_A}.p=0$ and $\mathrm{port_C}.p=0$ Leakage flow from B $\to$ A (given by GLeak). This is the load holding function. $\mathrm{pPreload}<\mathrm{port_B}.p$ $<$ $\mathrm{pFull}$ and $\mathrm{port_A}.p=0$ and $\mathrm{port_C}.p=0$ Flow from B $\to$ A. Valve is partially open. This is the pressure relief function. $\mathrm{pFull}<\mathrm{port_B}.p$ and $\mathrm{port_A}.p=0$ and $\mathrm{port_C}.p=0$ Flow from B $\to$ A. Valve is completely open. Flow rate is determined by ${q}_{\mathrm{nom}}$ and ${\mathrm{Δp}}_{\mathrm{nom}}$. $\mathrm{port_C}.p<\frac{\mathrm{pPreload}}{\mathrm{pressureRatio}}$ and $\mathrm{port_B}.p=0$ and $\mathrm{port_A}.p=0$ Leakage flow from B $\to$ A (given by GLeak). $\frac{\mathrm{pPreload}}{\mathrm{pressureRatio}}<\mathrm{port_C}.p$ $<$ $\frac{\mathrm{pFull}}{\mathrm{pressureRatio}}$ and $\mathrm{port_B}.p=0$ and $\mathrm{port_A}.p=0$ Flow from B to A. Valve is partially open. $\frac{\mathrm{pFull}}{\mathrm{pressueRatio}}<\mathrm{port_C}.p$ and $\mathrm{port_B}.p=0$ and $\mathrm{port_A}.p=0$ Flow from B $\to$ A. Valve is completely open. Flow rate is determined by ${q}_{\mathrm{nom}}$ and ${\mathrm{Δp}}_{\mathrm{nom}}$. This is the normal operation when the valve is opened by the pressure at the pilot. $\mathrm{port_A}.p<\mathrm{pCheckValvePreload}$ and $\mathrm{port_B}.p=0$ and $\mathrm{port_C}.p=0$ Leakage flow from B $\to$ A (given by GLeak). $\mathrm{pCheckValvePreload}<\mathrm{port_A}.p$ and $\mathrm{port_B}.p=0$ and $\mathrm{port_C}.p=0$ Flow from A $\to$ B through the check valve, given by qnomCheckValve and ${\mathrm{Δp}}_{\mathrm{nom}}$. $\mathrm{pPreload}<\mathrm{port_B}.p-\mathrm{port_A}.p\mathrm{backpressureRatio}+\mathrm{port_C}.p\mathrm{pressureRatio}$ and $\mathrm{port_B}.p-\mathrm{port_A}.p\mathrm{backpressureRatio}+\mathrm{port_C}.p\mathrm{pressureRatio}<\mathrm{pFull}$ Flow from B $\to$ A. Valve is partially open. $\mathrm{pFull}<\mathrm{port_B}.p-\mathrm{port_A}.p\mathrm{backpressureRatio}+\mathrm{port_C}.p\mathrm{pressureRatio}$ Flow from B $\to$ A. Valve is completely open. Flow rate is determined by ${q}_{\mathrm{nom}}$ and ${\mathrm{Δp}}_{\mathrm{nom}}$. 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 $\mathrm{Pa}$ 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. ${q}_{\mathrm{nom}}$ Nominal flow rate at dpnom of load holding valve (that is, the poppet). ${\mathrm{Δp}}_{\mathrm{nom}}$ Pressure drop at ${q}_{\mathrm{nom}}$. qnomCheckValve Nominal flow rate of check valve at ${\mathrm{Δp}}_{\mathrm{nom}}$. 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) $\left[\mathrm{Pa}\right]$.

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 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 $\mathrm{\nu }=\mathrm{Modelica.Media.Air.MoistAir.Utilities.spliceFunction}\left(x=\mathrm{Δp},\mathrm{pos}={\mathrm{\nu }}_{\mathrm{oil}}\left(p={p}_{A\left(\mathrm{abs}\right)},T=T,{v}_{\mathrm{air}}={v}_{\mathrm{gas}\left(\mathrm{oil}\right)},{p}_{\mathrm{sat}}={p}_{\mathrm{sat}}\right),\mathrm{neg}={\mathrm{\nu }}_{\mathrm{oil}}\left(p={p}_{B\left(\mathrm{abs}\right)},T=T,{v}_{\mathrm{air}}={v}_{\mathrm{gas}\left(\mathrm{oil}\right)},{p}_{\mathrm{sat}}={p}_{\mathrm{sat}}\right),\mathrm{Δx}=100\right)$ $\mathrm{\rho }=\mathrm{Modelica.Media.Air.MoistAir.Utilities.spliceFunction}\left(x=\mathrm{Δp},\mathrm{pos}={\mathrm{\rho }}_{\mathrm{oil}}\left(p={p}_{A\left(\mathrm{abs}\right)},T=T,{v}_{\mathrm{air}}={v}_{\mathrm{gas}\left(\mathrm{oil}\right)},{p}_{\mathrm{sat}}={p}_{\mathrm{sat}}\right),\mathrm{neg}={\mathrm{\rho }}_{\mathrm{oil}}\left(p={p}_{B\left(\mathrm{abs}\right)},T=T,{v}_{\mathrm{air}}={v}_{\mathrm{gas}\left(\mathrm{oil}\right)},{p}_{\mathrm{sat}}={p}_{\mathrm{sat}}\right),\mathrm{Δx}=100\right)$ $T={T}_{0\left(\mathrm{oil}\right)}+{\mathrm{ΔT}}_{\mathrm{system}}$ $q=\frac{{m}_{\mathrm{flow}\left(A\right)}}{\mathrm{\rho }}$ $\mathrm{Δp}={p}_{A\left(\mathrm{limited}\right)}-{p}_{B\left(\mathrm{limited}\right)}$ ${p}_{A\left(\mathrm{abs}\right)}={p}_{A}+{p}_{\mathrm{atm}\left(\mathrm{oil}\right)}$ ${p}_{A\left(\mathrm{limited}\right)}=\mathrm{max}\left({p}_{A},{p}_{\mathrm{vapour}\left(\mathrm{oil}\right)}-{p}_{\mathrm{atm}\left(\mathrm{oil}\right)}\right)$ ${p}_{B\left(\mathrm{abs}\right)}={p}_{B}+{p}_{\mathrm{atm}\left(\mathrm{oil}\right)}$ ${p}_{B\left(\mathrm{limited}\right)}=\mathrm{max}\left({p}_{B},{p}_{\mathrm{vapour}\left(\mathrm{oil}\right)}-{p}_{\mathrm{atm}\left(\mathrm{oil}\right)}\right)$

Variables

 Name Value Units Description Modelica ID $\mathrm{Δp}$ $\mathrm{Pa}$ Pressure drop dp $q$ $\frac{{m}^{3}}{s}$ Flow rate flowing into port_A q ${p}_{A\left(\mathrm{limited}\right)}$ $\mathrm{Pa}$ Limited gauge pressure pA_limited ${p}_{B\left(\mathrm{limited}\right)}$ $\mathrm{Pa}$ Limited gauge pressure pB_limited $\mathrm{\rho }$ $\frac{\mathrm{kg}}{{m}^{3}}$ Upstream density rho $\mathrm{\nu }$ $\frac{{m}^{2}}{s}$ Upstream kinematic viscosity nu ${p}_{A\left(\mathrm{abs}\right)}$ $\mathrm{Pa}$ Absolute pressure pA pA_abs ${p}_{B\left(\mathrm{abs}\right)}$ $\mathrm{Pa}$ Absolute pressure pB pB_abs $T$ $K$ Local temperature T ${p}_{A\left(\mathrm{summary}\right)}$ ${p}_{A}$ $\mathrm{Pa}$ Pressure at port A summary_pA ${p}_{B\left(\mathrm{summary}\right)}$ ${p}_{B}$ $\mathrm{Pa}$ Pressure at port B summary_pB ${\mathrm{Δp}}_{\mathrm{summary}}$ $\mathrm{Δp}$ $\mathrm{Pa}$ Pressure drop summary_dp ${q}_{\mathrm{summary}}$ $q$ $\frac{{m}^{3}}{s}$ Flow rate flowing into port_A summary_q ${P}_{\mathrm{hyd}\left(\mathrm{summary}\right)}$ $-\mathrm{Δp}q$ $W$ Hydraulic Power summary_HP ${p}_{\mathrm{sat}}$ [1] $\mathrm{Pa}$ Gas saturation pressure p_sat ${V}_{A}$ VolumeA ${V}_{B}$ VolumeB $\mathrm{CheckValve}$ CheckValve $\mathrm{Poppet}$ Poppet $\mathrm{counterBalanceBaseBlock}$ counterBalanceBaseBlock

[1] $\mathrm{oil.gasSaturationPressure}\left(T=T,{v}_{\mathrm{gas}}={\mathrm{oil.v}}_{\mathrm{gas}}\right)$

Connections

 Name Description Modelica ID ${\mathrm{port}}_{A}$ Layout of port where oil flows into an element ($0<{m}_{\mathrm{flow}}$, ${p}_{B}<{p}_{A}$ means $0<\mathrm{Δp}$) port_A ${\mathrm{port}}_{B}$ Hydraulic port where oil leaves the component (${m}_{\mathrm{flow}}<0$, ${p}_{B}<{p}_{A}$ means $0<\mathrm{Δp}$) port_B $\mathrm{oil}$ oil ${\mathrm{port}}_{C}$ Port where typically the control pressure for the pilot is connected port_C

Parameters

General Parameters

 Name Default Units Description Modelica ID ${\mathrm{ΔT}}_{\mathrm{system}}$ $0$ $K$ Temperature offset from system temperature dT_system use volume A $\mathrm{true}$ If true, a volume is present at port_A useVolumeA use volume B $\mathrm{true}$ If true, a volume is present at port_B useVolumeB ${V}_{A}$ ${10}^{-6}$ ${m}^{3}$ Geometric volume at port A volumeA ${V}_{B}$ ${10}^{-6}$ ${m}^{3}$ Geometric volume at port B volumeB ${p}_{\mathrm{preload}}$ $1.25·{10}^{7}$ $\mathrm{Pa}$ Load pressure to start opening valve pPreload ${p}_{\mathrm{Full}}$ $\frac{6}{5}{p}_{\mathrm{preload}}$ $\mathrm{Pa}$ Load pressure to open valve completely pFull $\mathrm{pressureRatio}$ $5$ Pressure ratio, i.e. multiplier for pilot pressure to open valve pressureRatio backpressure ratio $\mathrm{pressureRatio}$ Pressure ratio, i.e. multiplier for back pressure at port 2 to open valve; 0 for atmospherically vented valve backpressureRatio ${p}_{\mathrm{CheckValvePreload}}$ $1.25·{10}^{5}$ $\mathrm{Pa}$ Pressure to open check valve completely pCheckValvePreload ${G}_{\mathrm{leak}}$ ${10}^{-15}$ $\frac{{m}^{3}}{s\mathrm{Pa}}$ Conductance of leakage GLeak

Flow Parameters

 Name Default Units Description Modelica ID ${q}_{\mathrm{nom}}$ $0.001$ $\frac{{m}^{3}}{s}$ Nominal flow rate at dpnom of load holding valve qnom ${\mathrm{Δp}}_{\mathrm{nom}}$ $2.2·{10}^{6}$ $\mathrm{Pa}$ Pressure drop at qnom dpnom ${q}_{\mathrm{nom}\left(\mathrm{CV}\right)}$ ${q}_{\mathrm{nom}}$ $\frac{{m}^{3}}{s}$ Nominal flow rate at dpnom of check valve qnomCheckValve ${k}_{1}$ $10$ Laminar part of orifice model k1 ${k}_{2}$ $2$ Turbulent part of orifice model, ${k}_{2}=\frac{1}{{C}_{d}^{2}}$ k2