Automatic Flow Controls

Automatic Flow Controls. If the lowest rinsewater flow rate that can efficiently rinse a workpiece can be determined for a process line, this flow can then be automatically controlled to avoid variations arising from water line pressure changes or operator errors. 

Hence, as a result of the unsuitability and instability of the automatic flow-control system, an alternative means of control is required This can be achieved by setting up a control scheme baaed on pressure drops, the third key characteristic of the liquid/liquid hydrocydone. 

Automatic flow controllers have recently become available which operate in the 1-100 cm3/min flow range. These are voltage settable such that thumb wheels switches or potentiometers can be used to set the flowrate. These are specified at a repeatability of setpoint of about 0.2% and an accuracy of 1-2% of full scale. These flow controllers can easily be adapted to give a flow readout. The price of these units is still quite high at about ( 500 - 600) per channel but all indications are that they will be more widely used in the future. Typical specifications for three such devices are given in Table 6.4. 

Different feedstocks and/or solvents require different solvent to feed ratios. Each packing has a specific flooding point These two effects can lead to a great difference in mass flow. Because of this, pressures and temperatures should be controlled automatically. The flow must be measured exactly, preferably with a mass flow meter, but automatic flow control is not suitable for a multi-purpose plant The valves which are used for pressure and temperature control should be installed so that they can be replaced easily or adapted to new conditions. A very important requirement for the continuous operation of the plant is liquid level indication and control in the extractor and regenerator. Therefore the plant is equipped with capacitive level sensors which are part of a control circuit. The suitability of these sensors for measuring the level of oily products, vitamins and some type of hydrocarbons in supercritical systems have been tested in the lab previously. 

An automatic flow control valve, accurate within the expected pressure range, shall be installed to restrict flow to the maximum design flow of the treatment unit. 

A. Operation of Saturators. As shown in Fig. 11.1, neutralized depleted brine is fed to the saturatorfs). The total rate of flow is regulated in the upstream equipment, and no automatic flow control can be applied in the saturation system itself. The feed brine should be at pH 8 or 9, but an upset in the neutralization system could allow the pH to drop well into the acidic range. Although Monel is the metal normally used for instruments in alkaline brine applications, Hastelloy C has the advantage of a greater resistance to attack by acids. 

Process Hazards Analyses (PHAs) are also analyzed to ensure automatic flow controls and safe venting is there only. 

Figure 21.2. In practice, the flowrate is controlled by observing a measured flowrate while changing the valve stem position. The valve position continues to be adjusted until the desired flowrate is achieved. This approach forms the basis of the feedback control system used for many automatic flow control schemes and discussed further in Section 21.5. 

As 1 did not have reference to the pump curve in the field, 1 now proceeded as follows 1 switched the control valve from automatic flow control (FRC) to manual. The flow became steady, as did the discharge pressure and motor amperage. Now 1 understood the problem was not cavitation, but a control problem. 

For those columns with gravity return reflux, a severe oscillation in overhead vapor flow to the condenser is sometimes encountered. This is commonly called reflux cycle and has a typical period of several minutes. It has been observed primarily in columns where reflux flow is the difference between rate of condensation and distillate flow rate that is, where distillate is on automatic flow control or column-composition control. Reversing the controls—that is, employing automatic reflux flow or flow-ratio control and allowing distillate to be the difference flow—provides a positive cure. 

ANSWER Epoxy adhesives, which comprise both the adhesive component and the hardener, are usually mixed with a static mixer. It is possible to use and monitor automatic flow controllers on both components of the adhesive. However, the most common way to determine the correct mix ratio is to periodically take a sample of the mixed adhesive and measure its properties, including density, cure speed, bond strength, etc. 

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