Valves bellows

In some cases (mainly at sodium valve bellows leakages) the contact leakage detectors (of a spark-plug type) came into action. 

Helium turbine with gas seals, oil seals, bearings, cooling systems, insulation Helium compressor with gas seals, oil seals, bearings Helium/helium heat exchangers/recuperators, coolers Hot gas ducts with valves, butter fly valves, bellows, bends Helium purification Coatings in helium atmosphere... 

Hot Gas Ducts with Insulation. Regulation Valves. Bellows Hot eas Ducts... 

The component test loop (KVK) was provided for testing the main helium components of a nuclear process heat reactor concept (PNP) at 950 °C (max. 1050 °C for short periods). The main test components were helium to helium heat exchangers, hot gas ducts, hot gas valves, bellows, steam generators, a helium purification system, helium blowers and their acoustic emissions, helium leakage, control, and other miscellaneous systems and components. The overall operation time of the KVK amounts to more than 20,000 hours at 950 C or even higher temperatures. Its main operating parameters were ... 

Specification for Flanged Steel Globe Valves— Bellows 8 1997... 

Valve bellows Stainless steel 300 series Monel Bronze Stainless steel 300 series Monel Bronze... 

Metering Valve [X] ON/OFF Valve Bellows Valve Pressure Gauge. Heated Line... 

A mechanical device embodying a bellows-sealed needle valve with a lever reduction movement for fine control is shown in Fig. II, 23, 5. The needle is of stainless steel. This fine control valve assembly is useful for pressures ranging from 20 to 100 mm. of mercury when used in conjunction with a good water pump. 

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). 

Figures 29-19 and 29-20 illustrate two different mecbanical-hydraulic systems. Figure 29-19 is a bar-lift steam chest with a heavy-duty hydraulic seivo. The speed-sensing element is a flyball assembly attached to a rotating pilot. This rotating pilot sends a control-pressure signal that is proportional to speed to a bellows on the seivo. A change in control pressure initiated through the rotating pilot by either speed or speed changer deflects the bellows and seivo pilot valve. The seivopiston position is proportional to the control pressure.

The set pressure of a conventional valve is affected by back pressure. The spring setting can be adjusted to compensate for constant back pressure. For a variable back pressure of greater than 10% of the set pressure, it is customary to go to the balanced bellows type which can generally tolerate variable back pressure of up to 40% of set pressure. Table 2 gives standard orifice sizes. 

Balanced Bellows Safety Relief Valve - A balanced safety relief valve incorporates means for minimizing the effect of back pressure on the performance characteristics opening pressure, closing pressure, lift and relieving capacity. This is usually achieved by the installation of a bellows. 

Superimposed Back Pressure - Is the pressure at the outlet of the pressure relief valve while the valve is in a closed position. This type of back pressure comes from other sources in the discharge system it may be constant or variable and it may govern whether a conventional or balanced bellows valve should be used in specific applications. 

Spring Pressure - The spring pressure is equal to the set pressure minus the superimposed back pressure for a conventional PR valve. For a balanced bellows safety relief valve, the spring pressure equals the set pressure. 

A typical bellows PR valve is illustrated in Figure 4. Bellows valves are generally specified where any of the following apply ... 

The service is fouling or corrosive, since the bellows shields the spring from process fluid. Note, however, that the bellows convolutions could also foul in extremely viscous service, such as asphalt, limiting the lift of the valve unless the valve is heated and insulated. 

Figure 4. Typical balanced bellows safety relief valve.

In addition to the above back pressure limitations based on valve capacity, balanced bellows PR valves are also subject to back pressure limitations based on the mechanical strength of the bellows or bellows bonnet, or the valve outlet flange rating. The back pressure specified for the valve is governed by the lowest back pressure permitted by these various criteria. 

When the pilot exhausts to the atmosphere, a pilot-operated PR valve is fully balanced. Like the balanced bellows valve, therefore, its opening pressure is unaffected by back pressure, and high built-up back pressure does not result in chattering. 

For applications involving unusually high superimposed back pressure, a pilot operated valve may be the only possible balanced valve that is commercially available, because of the mechanical limitations which apply to bellows. 

They are higher-cost in smaller sizes, compared with conventional and bellows valves. 

The application of pilot-operated PR valves is limited to clean services, where they are an acceptable alternative to the bellows valve if a balanced characteristic is required. Their particular advantage is freedom from "simmer", which may permit a closer operating pressure/set pressure margin than normal. 

A balanced bellows PR valve is one in which the closing force exerted by back pressure on the top of the valve disc and the back pressure exerted on the bottom of the disc are balanced by equal surface exposure, thus cancelling each other. The bellows shields the top of the disc from back pressure and the bellows area is vented to the atmosphere via the bonnet vent. 

Figure 6. Forces acting on discs of conventional and balanced bellows safety relief valves.

Balanced bellows valves need no reduction in spring pressure to compensate for superimposed back pressure, and they can tolerate variable superimposed back pressure without an effect on opening pressure. 

Balanced bellows PR valves need not be restricted to the same built-up back pressure limit (10% of set pressure) as are conventional valves, since they are not subject to chattering from this cause. However, maximum back pressure is limited by capacity and in some cases by the mechanical design strength limitations of parts such as the outlet flange, bellows, or valve bonnet. 

In general, the total back pressure on a balanced bellows pressure relief valve (superimposed plus built-up) should be limited to 50% of set pressure, because of the marked effect of higher back pressures on valve capacity, even when appropriate correction factors are used in sizing. In exceptional cases, such as a balanced bellows PR valve discharging into another vessel, total pressure up to 70% of set pressure may be used. 

It is important to note that back pressure affects balanced PR valve capacities in the same way as for conventional valves, and appropriate factors are included in the sizing procedures. They are subject to the same recommended limits of maximum total back pressure (superimposed plus built-up) as conventional valves. In the case of balanced bellows valves, mechanical considerations must also be evaluated, since they may limit the maximum permissible back pressure. 

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