Diaphragms, regulator

A. Flow Control without Feedback. Plow can be controlled by means of a needle valve if the pressure drop across the valve is constant. The pressure on the upstream side often can be held constant with a single- or two-stage mechanical diaphragm regulator (Section 10.1. B). If the stream of gas does not experience a variable constriction after the needle valve, the above combination provides a simple and convenient means of providing a steady flow. Often an arrangement such as this is used in conjunction with a rotameter or electronic mass flow meter (Fig. 7.14). 

A metal diaphragm regulator should be used for pressure regulation. 

The use of metal diaphragm regulators to minimize air diffusion leakage... 

Bellows or Dia.phra.gm Meters. Bellows meters use flexible diaphragms as the metering chambers. A series of valves and linkages control the filling and emptying of the chambers. Movement of the flexible walls is regulated for a constant displacement per stroke. Meters of this type are widely used in the gas industry as residential meters (see Gas, natural). 

To avoid this situation, some regulators are designed with a built-in over-pressure relief mechanism. Over-pressure relief circuits usually are composed of a spring-opposed diaphragm and valve assembly that vents the downstream piping when the control pressure rises above the set point pressure. 

A condenser pressure regulator can be in the form of a pressure-operated bleed valve in a bypass across the condenser, to divert hot gas to the receiver. The valve diaphragm is balanced by a pre-set spring and will open the bypass if the condensing pressure falls. A similar effect can be obtained by a pressure-operated valve between the condenser and the receiver, to restrict the flow and allow liquid to accumulate in the condenser, reducing its efficiency. For operating... 

We have to make a distinction here between electric controllers (e.g. PID controllers) with a proportional valve as actuator and mechanical diaphragm controllers. In a regulation system w/ith electric controllers the coordination between controller and actuator (piezoelectric gas inlet valve, inlet valve A/ith motor drive, butterfly control valve, throttle valve) is difficult because of the very different boundary conditions (volume of the vessel, effective pumping speed at the vessel, pressure control range). Such control circuits tend to vibrate easily when process malfunctions occur. It is virtually impossible to specify generally valid standard values. 

Many control problems can be better solved with a diaphragm controller. The function of the diaphragm controller (see Fig. 3.27) can be easily derived from that of a diaphragm vacuum gauge the blunt end of a tube or pipe is either closed off by means of an elastic rubber diaphragm (for reference pressure > process pressure) or released (for reference pressure < process pressure) so that in the latter case, a connection is established between the process side and the vacuum pump. This elegant and more or less automatic regulation system has excellent control characteristics (see Fig. 3.28). 

Pressure regulation by means of diaphragm confroller with external automatic reference pressure adjustment (see Fig. 3.31)... 

For automatic vacuum processes with regulated process pressure, presetting of the desired set pressure must often function and be monitored automatically. If a diaphragm controller is used, this can be done by... 

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