Hydraulic systems protective devices

A filter with a bypass housing only provides complete protection for the hydraulic system when the bypass is closed, as in normal use. A non-bypass housing is essential when all the fluid must be filtered all the time. In this case the onset of clogging, cansing an increase in differential pressure to a predetermined level, can trigger a visnal and/or audible alarm, via a pressure switch, or similar device. 

Turcon CTo is an electrohydraulic rapid trigger shut-off device being a special version of the gate valve. Turcon CTo is used mainly as a monitoring system resp. as an rpm protection device for high-rpm steam turbines. It offers major advantages compared with the mechanical-hydraulic systems available hitherto ... 

Nowadays, pressures and flow in the process industry are controlled by electronic process systems and highly sophisticated instrumentation devices. Almost all control systems are powered by an outside power source (electric, pneumatic, hydraulic). The law requires that when everything fails regardless of the built-in redundancies, there is still an independent working device powered only by the medium it protects. This is the function of the SRV, which, when everything else works correctly in the system, should never have to work. However, practice proves the contrary, and there are a variety of incidents which will allow the system pressure to exceed the design pressure. 

Fig. 6.7-29 Photograph and diagram of a dry-bag CIP system (courtesy Dorst, Kochel am See, Germany). 1, protective enclosure 2, control cabinet 3, hydraulic unit 4, high-pressure intensifier pump 5, loading device 6, hopper 7, dosing device ...

The design of hydraulic engineered safety features for LWRs has traditionally been performed according to high reliability and leak proof standards. These systems are usually called into operation to protect the fuel barrier in the case of a loss of the primary system barrier. In addition, being strictly connected to the primary circuit pressure boundary, they have to be equipped with leak proof isolation devices, normally closed during plant operation. 

Relief valves and inlet check valves are simple devices that suppress the unsteady effects of an over-pressure or under-pressure, respectively. The relief valve is fitted against an aperture in the pipe by means of a spring whose stiffness is chosen so as to allow the valve to open, should the over-pressure exceed a limiting value. Some liquid is then forced out of the pipe, thus decreasing the pressure in the pipe. The inlet check valve operates in the opposite manner, opening inwards of the pipe when the pressure drops below a limiting value. The mass of the valves and the spring constants should be chosen in such a way that the characteristic frequency of the protective system differs from the characteristic frequency I/4 of the hydraulic... 

To limit the scope of possible leaks of sodium from the external primary coolant systems additional jacketing was provided for pipelines to the second isolation valves including the valve casings. Similar measures with installation of an additional valve are planned for the spent fuel drum cooling system to prevent failure due to faults or leaks in the isolation valves. Passive safety devices (hydraulic seals) are installed for overpressure protection of the drum s main and guard casings. 

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