Control valve gas flow

Manufacturers have found that gas flow at high valve pressure ratios, pi p, may be calculated using the same equation as for liquid flow  

It is important for its practical use that any model of gas flow through the control valve shall require no more data than are customarily provided by valve manufacturers. Given the valve inlet and outlet pressures, the inlet specific volume, the valve opening and the type of gas being passed, the method presented in the main part of this chapter will require only the two conductances, C,. and C, both of which are supplied as a matter of course by manufacturers of control valves or else may be derived from the corresponding pair of values provided after units conversion. 

2 Representing the first section of the controi vaive as a nozzle 

The gas flow through the control valve as a whole will be very close to adiabatic, and, as just noted, the expansion as far as the valve throat will incur only a small frictional loss, implying a process that is approximately isentropic. Accordingly we may substitute the ratio of the gas s specific heats, y = Cp/c,. for the polytropic index, n, in the flow equations (5.25) and (5.26) derived for an ideal nozzle in Chapter 5. Combining those two equations gives the mass flow, W, as  

Following the procedure of Section 5.3, we may differentiate equation (9.3) with respect to throat pressure ratio and set the result to zero to show that the maximum flow occurs when the throat pressure ratio has decreased to a critical value given by  

---

Appendix 4 Comparison of Fisher Universal Gas Sizing Equation, FUGSE, with the nozzle-based model for control valve gas flow... 

A4.3) reducing to the choked gas equation (9.2). But while the FUGSE will be valid at either end of the range of pressure ratios, the fact that the sine function joins the extremes in a conveniently smooth manner does not guarantee that the formula will be accurate at intermediate values. This appendix examines how closely the FUGSE matches direct data and the nozzle-based method for calculating control valve gas flow. 

Gas compressor anti-surge (GM-OFF) control circuit, comprising transmitters, computers and pneumatic control valve Reverse flow protection (on axnal compressors only) as supplementary protection device against surging, working independently of the control circuit Expander emergency stop valve with pneumatic actuator and solenoid valve... 

Choking, or expansion of gas from a high pressure to a lower pressure, is generally required for control of gas flow rates. Choking is achieved by the use of a choke or a control valve. The pressure drop causes a decrease in the gas temperature, thus hydrates can form at the choke or control valve. The best way to calculate the temperature drop is to use a simulation computer program. The program will perform a flash calculation, internally balancing enthalpy. It will calculate the temperature downstream of the choke, which assures that the enthalpy of the mixture of gas and liquid upstream of the choke equals the enthalpy of the new mixture of more gas and less liquid downstream of the choke. 

Are vaporizers provided with automatic gas line shutoff valve, downstream pressure-reducing valve, gas flow control valve, temperature control system and interlocks to shut down gas flow on low vaporizer temperature, and appropriate alarms in a continuously manned control room ... 

Fig. 1.15. Dispensing gas directly from a tank. The needle valve is used to control the gas flow into the solution, and a mercury-filled bubbler prevents excessive pressure buildup.

Presently a commercially available two stage vacuum system comprising a membrane (Pfeiffer MVP 006-4) and a turbo pump (Pfeiffer HiPace 10) in combination with a pressure sensor (Leybold Vacuum Ionivac ITR 90) establish a pressure of about 0.1 Pa in the system. Three electric valves are used to control the gas flow into the capillary system and for the bypasses. The use of macro devices simplifies the handling of the experimental setup and also the electronic control. Pressure drops for plasma and sample gases are accomplished by an appropriate combination of capillaries with different diameters and lengths as described in Sect. 4. 

The samples were oxidized using a commercial plasma discharge unit (Plasmod registered trademark of Tegal Corporation, Richmond,California), which operates at 13.56 MHz and has a variable power output from 0 to 100 watts. A variable leak valve (Granville-Phillips Company, Boulder, Colorado), a three-way valve and other modifications were added to provide a better vacuum, to control the gas flow rate and to control the gas pressure. 

The role of this system is to generate precursor vapour, and then deliver it to the CVD reactor. Gaseous precursors are preferred because they can be readily metered to control the gas flow parameters. Liquid and solid reactants can usually be vaporised at suitable temperatures and transported by a carrier gas to the reaction chamber. A typical gas delivery system with four delivery lines is shown in Figure 3.3. In lines 1, 2 and 3 gas flows and their associated parameters (e g. flow rate, pressure) are regulated by three mass flow controllers and the relevant valves. H2, MTS-H2 and Ar gases are conveyed to the gas mixer, then to the CVD chamber. Line 4 is employed to purge the reactor before and after the CVD process. For a delivery system, three types of precursors should be considered. 

Needle valves are used to accurately control the gas flow in the gas lines, while butterfly valves are employed to regulate the gas flow and the pressure in the CVD reaction chamber. 

The ARSA system is designed to operate continuously in remote areas with minimal maintenance and consumables limited to replacement bottles of nitrogen carrier gas and CO2 removal traps. Dryers and gas traps were chosen that could be automatically regenerated in the field. The system has many components and a complex path for the analyte gas that traverses the system. The numerous valves ( 100) for controlling the gas flow and trap regeneration processes require a control system about one order of magnitude more complex than that for the RASA system described in the preceding section, if the number of parts is taken as a measure of... 

SUCTION SERVICE VALVE - Two-way manually operated valve located at the inlet to compressor. It controls suction gas flow and is used to service unit. 

---