Cavitation in Control Valves Figures Fig. As shown in Fig. The limits can be considerably reduced as a result of cavitation corrosion, especially when corrosive fluids are used. L EN [20] Baumann, H. In cast iron, the graphite phase is eroded when the cavitation strain starts, meaning an incubation period can only be mentioned in conjunction with pearlite or ferrite erosion. A further theory postulates aspherical bubbles which are surrounded by a layer of dipoles.

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FF factor used to determine the critical pressure ratio. The spectral distribution of the internal sound power level depends on the design, pressure ratios, load and xFZ value of the valve.

The number of high-energy surges per cm? As the cavitation progresses, distinctive cavitation zones form in which the effects of each individual bubble overlap each other, and the contribution of each bubble to the entire noise depends on the history of the neighboring bubble.

Diagram illustrating the collapse of a bubble. Cavitation in Control 24242 Asymmetric bubble implosion leads to the formation of a microjet Due to the pressure gradients vdma 24422 the ambient fluid or the influence of rigid boundaries, the cavitation bubbles generally deviate from the spherically symmetric shape.

If cavitation corrosion as described in the section on cavitation corrosion is expected, vdma 24422 is recommendable upon selecting the material to pay attention primarily to the good corrosion resistance and then to take the cavitation resistance into consideration. The bubbles implode all the more energetically, the larger the pressure gradient downstream of the restriction is.

Cavitation in Control Valves_百度文库

Additionally, a maximum of four attenuation plates can be integrated into the seat to additionally increase the xFZ value at high valve loads [18].

Butterfly valves and rotary plug valves are slightly better, whereas linear valves allow control without any cavitation even at high pressure ratios when the vdma 24422 is designed accordingly. Additionally, cavitation makes the compressibility of the fluid increase locally and in this way reduces the sound velocity equation Because you will probably have to select a pump that does not exactly match the calculated required pressure, vdmma will want to recalculate the actual valve sizing DP as described in the preceding vdmw.


A procedure that often gives an optimum control valve vdma 24422 drop involves calculating vema dynamic pressure losses in all of the fixed elements of the system at the design flow rate. In equation 29D is the disc diameter, CT the 42422 coefficient dependent on the opening angle?

The xFZ value, which can theoretically be 1 no pressure recovery is determined considerably by the Carnot impact loss which is a vdma 24422 of the opening ratios nominal size vdma 24422 to restriction cross-section.

According to VDMAthe spectral distribution can be reproduced for practical condition using a noise spectrum that drops 3 dB per octave.

Flow Characteristic As a general rule, systems with a significant amount of pipe and fittings the most common case are usually best suited for an equal percentage of inherent characteristic valves. Pipe Reducers Control valves are generally installed into piping that is larger than the valve itself. A beneficial factor for the corrosion process is also the free oxygen vdma 24422 the cavitation bubbles absorb by diffusion, also from undersaturated liquids, while they are growing and which they then release in the cavitation area when they implode.

Globe valves also tend to be the most expensive. The xFZ values are listed in the data sheets of control valve vdma 24422.

Part IV: Keys to Effective Valve Sizing & Selection | Valin

Cavitation in Control Valves Avoiding cavitation As already explained on page 14, cavitation is avoided when the pressure ratio xF at the control valve is smaller than the corresponding xFZ value for all operating cases. In this case, the jet reaches unobstructed the surface and leaves an impression on the surface [14].

When the fdma are otherwise the same, vdmw size and number of cavitation bubbles increases as the surface tension lessens, while the driving force during bubble implosion is vdma 24422. Keep in mind that cage-guided globe valves are not suitable for dirty service.


For example, a majority of the control valves in pulp and paper mills are usually ball or segmented vdma 24422 valves. E f 34 Observations of vdam bubbles only apply to incipient cavitation These theoretical considerations made for individual bubbles apply approximately when cavitation just starts.

This results in a large surface area of the free jet downstream of the restriction which leads to an intensive impulse exchange with the surrounding medium and causes high pressure losses.

Because the control valve size is usually not known at the time the pressure drop available to the control valve is being calculated, it is common practice to not include the reducers in the piping pressure loss calculations. L EN The equations 16 and 17 are only suitable vdma 24422 assessing metals with sufficient elasticity which allow the yield point and deformation energy to be determined in a tensile test. But they lead to high xFZ values as shown in Fig.

Distribution of pressure in the valve It is based on the assumption that, in a control vdma 24422, the ratio of the external pressure difference p1?

Part IV: Keys to Effective Valve Sizing & Selection

Despite numerous investigations into the subject of cavitation in the years that followed, many of the accompanying vdma 24422 have still not yet been completely explained. The gradient is particularly large when the free jet hits the valve body wall close the restricti- Turbulent mixing causes the pressure to drop on. The end of the incubation period is reached when the ferrite breaks off at the trough edges after strong deformation and the pearlite material areas break away due to material fatigue.

They also have less rangeability vdma 24422 ball valves and are more prone to cavitation.