Counterbalance Valve (IL)

High-pressure regulation valve in an isothermal liquid system

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• Simscape / Fluids / Isothermal Liquid / Valves & Orifices / Flow Control Valves

• Description

The Counterbalance Valve (IL) block models a normally closed pressure control valve in an isothermal liquid network. A counterbalance valve is commonly used when high-pressure events are expected or when controlled manipulation at high pressures is required, such as hydraulic overloading or lowering suspended loads. The valve functions under a force balance between a spring and the backing pressure at port B and the load pressure at port L. When the monitored pressure line, the pilot pressure at port P, exceeds the pressure at port B, the valve begins to open.

There is no flow between ports B and P or between ports L and P.

Valve Opening

The counterbalance valve operates under the force balance:

${p}_{pilot}{A}_{pilot}+{p}_{load}{A}_{load}={p}_{back}{A}_{back}+{F}_{set},$

where:

• ppilot is the pressure at port P.

• pload is the pressure at port L.

• pback is the pressure at port B.

• Fset is the accumulated force due to the spring and preloading at port B.

The port areas Apilot, Aload, and Aback are set by the Pilot ratio:

${R}_{pilot}=\frac{{A}_{pilot}}{{A}_{load}},$

and the Back pressure ratio:

${R}_{back}=\frac{{A}_{back}}{{A}_{load}}.$

A ratio of 4:1 or 3:1 is typical for counterbalance valves.

The preset force, Fset, represents the spring preloading and spring force at port B, which are characterized as a Set pressure differential, pset:

${F}_{set}={p}_{set}{A}_{load}.$

Opening Parameterization

The linear parameterization of the valve area, for normally open valves, is:

${A}_{valve}=\stackrel{^}{p}\left({A}_{leak}-{A}_{\mathrm{max}}\right)+{A}_{\mathrm{max}},$

and for normally closed valves is:

${A}_{valve}=\stackrel{^}{p}\left({A}_{\mathrm{max}}-{A}_{leak}\right)+{A}_{leak}.$

The control compensator normalized pressure, $\stackrel{^}{p}$, is:

$\stackrel{^}{p}=\frac{\left({p}_{load}+{p}_{pilot}{R}_{pilot}-{p}_{back}{R}_{back}\right)-{p}_{set}}{\left({p}_{\mathrm{max}}-{p}_{set}\right)},$

where:

• pset is the Set pressure differential.

• pmax is the Maximum opening pressure differential.

The normalized check valve pressure is:

$\stackrel{^}{p}=\frac{{p}_{control}-{p}_{cracking}}{{p}_{\mathrm{max}}-{p}_{cracking}}.$

where:

• pcracking is the Cracking pressure differential.

• pmax is the check valve Maximum opening pressure differential.

At the extremes of the control and check valve pressure ranges, you can maintain numerical robustness in your simulation by adjusting the block . With a nonzero smoothing factor, a smoothing function is applied to every calculated pressure, but primarily influences the simulation at the extremes of these ranges.

When the Smoothing factor, s, is nonzero, a smoothed, normalized pressure is instead applied to the valve area:

${\stackrel{^}{p}}_{smoothed}=\frac{1}{2}+\frac{1}{2}\sqrt{{\stackrel{^}{p}}_{}^{2}+{\left(\frac{s}{4}\right)}^{2}}-\frac{1}{2}\sqrt{{\left(\stackrel{^}{p}-1\right)}^{2}+{\left(\frac{s}{4}\right)}^{2}},$

In the Tabulated data parameterization, the smoothed, normalized pressure is also used when the smoothing factor is nonzero with linear interpolation and nearest extrapolation.

Ports

Conserving

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Load port and liquid exit port from the valve.

Back pressure port and liquid entry port to the valve.

Control, or pilot, pressure port. When the combined pressure at P and B exceeds the backing and spring pressures, the check valve between ports B and L opens.

Parameters

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Model Parameterization

Method of modeling the opening of the valve. The opening is either parametrized linearly, which correlates the opening area to the control member opening stroke, by user-supplied data that correlate the valve opening area to the pressure differential over the valve.

Pressure contribution of the compressed spring before valve operation.

The maximum compensator valve pressure.

Maximum open area of the orifice in the load line. Internally, this orifice is connected in parallel with the load line check valve. The orifice and check valve can have different cross-sectional areas.

Dependencies

To enable this parameter, set Valve parameterization to Linear.

Sum of all gaps when the valve is in the fully closed position. Any area smaller than this value is saturated to the specified leakage area. This contributes to numerical stability by maintaining continuity in the flow.

Vector of valve opening areas for the tabular parameterization of the valve opening area. The vector elements must correspond one-to-one with the elements in the Pressure differential vector parameter. The elements are listed in ascending order and must be greater than 0.

Dependencies

To enable this parameter, set Valve parameterization to Tabulated data - Area vs. control member travel.

Vector of pressure differential values for the tabular parameterization of the valve opening area. The vector elements must correspond one-to-one with the elements in the Opening area parameter. The elements are listed in ascending order and must be greater than 0.

Dependencies

To enable this parameter, set Valve parameterization to Tabulated data.

Ratio of the pilot port area to the load port area.

Ratio of the back pressure port area to the load port area.

Correction factor that accounts for discharge losses in theoretical flows.

Upper Reynolds number limit for laminar flow through the valve.

Whether to account for transient effects to the fluid system due to opening the valve. Setting Opening dynamics to On approximates the opening conditions by introducing a first-order lag in the pressure response. The Opening time constant also impacts the modeled opening dynamics.

Continuous smoothing factor that introduces a layer of gradual change to the flow response when the valve is in near-open or near-closed positions. Set this value to a nonzero value less than one to increase the stability of your simulation in these regimes.

Constant that captures the time required for the fluid to reach steady-state conditions when opening or closing the valve from one position to another. This parameter impacts the modeled opening dynamics.

Dependencies

To enable this parameter, set Opening dynamics to On.

Check Valve

Pressure differential value that triggers the valve to open.

Maximum valve pressure. This value bounds the pressures at the valve exit to maintain physical values during simulation.

Maximum open area of the check valve in the load line. Internally, this check valve is connected in parallel with a load line orifice. The orifice and check valve can have different areas.

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