Oscillating valve

In a low pressure programmer, the solvent from each reservoir passes to an oscillating valve, instead of flowing directly to a pump,... 

The war itself also drove the development of improved and miniaturised electronic components for creating oscillators and amplifiers and, ultimately, semiconductors, which made practical the electronic systems needed in portable eddy current test instruments. The refinement of those systems continues to the present day and advances continue to be triggered by performance improvements of components and systems. In the same way that today s pocket calculator outperforms the large, hot room full of intercormected thermionic valves that I first saw in the 50 s, so it is with eddy current instrumentation. Today s handheld eddy current inspection instrument is a powerful tool which has the capability needed in a crack detector, corrosion detector, metal sorter, conductivity meter, coating thickness meter and so on. 

To prevent surges, a well-trained operator would put the controller in manual mode and freeze the valve in an open position. This stops the control loop oscillations and decreases the compressor discharge resistance, thus breaking the surge cycle. Unfortunately, the operator has no way of knowing how much to open the valve and, subsequently, how much to close it. 

Schwing-kreis, m. oscillating circuit circuit, -kristall, m. crystal oscillator, -neigung, /. oscillating tendency. -lohr, n. swing pipe, -rohre, /. oscillatory valve. 

The pressure drop remains essentially constant as long as the liquid flow on tray remains steady during the period point A to point B on the diagram (the open balance point) [201]. At point B all valves are completely open off their seats, but are on the verge of closing and may be oscillating from open to closed. At point B the vapor velocity through the holes, opened balance point is ... 

The effect of resistances and capacities in the air line and water feed has been studied theoretically and it has been shown that oscillations will tend to be stable if there is a large air capacity downstream from the control valve, and the inclusion of a resistance in the water supply line should dampen them. 

Oscillations occur because the liquid column requires more than the equilibrium quantity of air to produce the initial acceleration. It therefore becomes over-accelerated and excess of liquid enters the limb with the result that it is retarded and then subsequently has to be accelerated again. During the period of retardation some liquid may actually run backwards this can readily be prevented, however, by incorporating a non-return valve in the submergence limb. 

Each solvent passes from its reservoir directly to a pump and from the pump to a mixing manifold. After mixing, the solvents pass to the sample valve and column. The pumps control the actual program and are usually driven by stepping motors. The volume delivery of each solvent is controlled by the speed of the respective pump. In turn, the speed of each motor is precisely determined by the frequency of its power supply which can be either generated by external oscillators or, if the chromatograph is computer controlled, directly from the computer itself. 

The manifold also receives and mixes solvents from each of the programmed valves. The valves are electrically operated and programmed to open and close for different periods of time by adjusting the frequency and wave form of the supply. Thus, a predetermined amount of each solvent is allowed to flow into the manifold. The valves can be driven by oscillators contained in a separate electronic programmer or if the chromatograph is computer controlled, the controlling waveform and frequency can be provided directly from the computer. 

Several devices are also available to promote airway clearance. Flutter valve devices employ oscillating positive expiratory pressure (OPEP) to cause vibratory air flow obstruction and an internal percussive effect to mobilize secretions. Intrapulmonary percussive ventilation (IPV) provides continuous oscillating pressures during inhalation and exhalation. Finally the most commonly used technique is high-frequency chest compression (HFCC) with an inflatable vest that provides external oscillation. Vest therapy is often preferred by patients because they can independently perform the therapy even from an early age.5,14... 

Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant, or on implanted material in the absence of an alternative anatomic explanation, or Abscess, or... 

These oscillations may cause an additional heat flux into the dewar and vibrations which disturb delicate experiments. Often the geometry is changed by the insertion of an additional volume or adding a damping valve. 

A piston compressor (in case of a Stirling type PTR) or a combination of a compressor and a set of switching valves (GM type PTR) are used to create the pressure oscillations. The regenerator of a PTR stores the heat of the gas during a half-cycle and, therefore, must have a high heat capacity, compared to the heat capacity of the gas. 

In the GM-type PTR (mostly used at present), a compressor produces continuous high and low pressures and uses a rotary valve to generate pressure oscillations in the pulse tube. In the Stirling-type PTR, pressure oscillations are created by the movement of a piston, directly connected to the pulse tube and controlled by a motor. 

Figure 1. Diagram of apparatus (M) monomer reservoir (F) flow meter (VG) vacuum gage (mercury manometer) (E) electrode (T) liquid nitrogen trap (P) mechanical pump (V,) needle valve (Vt) stop valve (Vs) pressure control valve (OSC) discharge frequency oscillator (AMP) amplifier (1MC) impedance matching circuit...

M. Perez and P. Albertos. Self-oscillating and chaotic behaviour of a PI-controlled CSTR with control valve saturation. J. Process Control, 14 51-59, 2004. 

It is interesting to note that in chaotic regime, the flow rate outlet stream, which is manipulated by the control valve CVl (see Figure 12), and the reactor volume, are driven by the PI controller to the equilibrium point without chaotic oscillations. However, the other variables have a chaotic behavior as shown in Figure 18. So it is possible to obtain a reactor behavior, in which some variables are in steady state and the others are in regime of chaotic oscillations, due to the decoupling or serial connection phenomena. In this case the control system and the volumetric flow limitation of coolant flow rate through the control valve VC2, are the responsible of this behavior. Similar results can be obtained from model. 

In order to reduce the cooling level to the barrel zone, a metering valve was placed in the water line upstream of the solenoid valve as shown in Fig. 12.8(b). Now when the controller opens the solenoid valve, a much lower quantity of water and thus cooling is available to the barrel zone. Prior to this modification, the barrel temperatures oscillated 10 °C about the set point temperature. After the modification, the temperature oscillations were reduced to about 3 °C, and the profitability of the process was improved due to the minimization of resin consumption. 

The output of the digester is pumped from the helix through a pneumatically actuated valve either into the neutralization vessel or to waste. A pump was designed and built for this purpose. Its action is based on an oscillating piston, it has no moving valves and the hot acid comes into contact only with Kel-F and PTFE. The maximum flow-rate is about 12 ml min. This pump has been described in more detail elsewhere [33]. 

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