The sizing equation for the choked flow base fluid tells us that the fluid flow control valve is proportional to the square root of the differential pressure. This simple relationship is shown in green by the graph in Figure 1.(Note that the scale of the horizontal axis is pressure drop. Square root) This linear relationship is not always true. When the pressure drop increases, the flow reaches a point where it no longer increases. Once this happens, the increased increase in pressure drop across the valve does not result in additional flow, which is choking. Here we refer to this as the terminal pressure drop of the limiting or suffocating pressure drop, ΔPT.(The same thing is sometimes referred to as allowable pressure drop, ΔP allowable sometimes, when the maximum pressure drop, ΔP max, and sometimes the critical pressure drop, ΔP crit.) Figure 1. Fluid flow at a control valve as a function of pressure drop across the valve. Let's take a look at what's happening inside the valve to smother this flow. The flow velocity reaches a maximum as the flow of water contracts through the cavity (at which point the cross-sectional area of the flow is at a minimum). Energy saving provides that since the kinetic energy in the systolic flow increases to a maximum, the potential energy, in the formation of static pressure, must be Radiator Heater Valve reduced to a minimum.Note that in the figure, ΔP is less than ΔPT and the flow does not choke.Velocity and pressure distribution for clog-free flow control valves. As the pressure drop across the valve increases, so does the flow. Increase the speed in the retraction and decrease the pressure in the cavity contracta. If the cavity contracta pressure is lower than the vapor pressure, the vapor bubbles form in the systolic flow. Because the steam occupies a much larger volume of liquid, the feeding of the steam bubbles and any additional reduction in downstream pressure will only result in larger and larger foam, but no increase in flow. It is the shrunken flow that makes the flow the formation of these bubbles. Cavitation Figure 3 shows the suffocating process and cavitation is discussed in the next paragraph.
