Physical Properties and Failure Analysis for Bolts in the Diaphragm Valve by Micro Morphology and Metallographic Test

The reasons leading to the fracture of 17-4PH stainless steel bolts in the isolation valve of a power plant was analysed by means of morphology analysis, chemical analysis, hardness test, metallographic test, pitting corrosion test and intergranular corrosion test, SEM and other detection means. The results show that there are many corrosion pits on the surface of the valve stem in the seawater system, the corrosion pits is extend and propagation in intergranular cracking. The main reasons to valve stem fracture are the low corrosion resistance of the material and the improper aging process of heat treatment.

Design and Analysis of an Aerostatic Pad Controlled by a Diaphragm Valve

Because of their distinctive characteristics, aerostatic bearings are particularly suitable for high-precision applications. However, because of the compressibility of the lubricant, this kind of bearing is characterized by low relative stiffness and poor damping. Compensation methods represent a valuable solution to these limitations. This paper presents a design procedure for passively compensated bearings controlled by diaphragm valves. Given a desired air gap height at which the system should work, the procedure makes it possible to maximize the stiffness of the bearing around this value. The designed bearings exhibit a quasi-static infinite stiffness for load variation ranging from 20% to almost 50% of the maximum load capacity of the bearing. Moreover, the influence of different parameters on the performance of the compensated pad is evaluated through a sensitivity analysis.

Dynamic behaviour and stability analysis of a compensated aerostatic pad

Thanks to their low friction, aerostatic pads have important applications in precision positioning systems and linear guides. A simple and cheap solution to increase the static stiffness of aerostatic pads is to add a proper designed pneumatic valve to regulate the air flow supplied to the bearing. However, integrating aerostatic pads with additional devices can reduce its dynamic performance. This paper presents a numerical study on the dynamic behaviour and stability a commercial aerostatic pad controlled by a custom-built diaphragm valve. The bearing performance is studied by means of a lumped parameters model. Air bearing stiffness and damping are analysed in the frequency domain. Subsequently, the lumped model is linearized to investigate the stability of the system by means of Routh-Hurwitz method. The performance of the controlled air pad is compared to that of a simple commercial air pad.

A Pressure-Tight Sampler with Flexible Titanium Bag for Deep-Sea Hydrothermal Fluid Samples

This paper details the development and application of a novel pressure-tight sampler with a metal seal capable of acquiring high-purity fluid samples from deep-sea hydrothermal vents. The sampler has a titanium diaphragm valve for sampling and a flexible titanium foil bag to store the fluid sample. Hence, all parts of the sampler in contact with the sample are made of titanium without elastomer O-ring seals to minimize the organic carbon blank of the sampler, which makes it suitable for collecting organic samples. A pressure-tight structure was specially designed to maintain the sample at in situ pressure during the recovery of the sampler. The sampler has been successfully tested in a sea trial from November 2018 to March 2019, and pressure-tight hydrothermal fluid samples have been collected.

On the Design of a Diaphragm Valve for Aerostatic Bearings

Because of their almost zero friction, cleanness and long life, aerostatic bearings are commonly used in many applications where high precision of positioning is required, e.g. machine tools, measuring machines, semiconductor manufacturing and power board testing. However, air bearings suffer from low relative stiffness and poor damping. Active and passive compensation are two effective methods to enhance the static and dynamic performance of these kinds of bearings. Despite their higher performance, active compensation solutions are too expensive to be used in industrial applications, as a consequence of the costs related to their controllers, actuators and sensors. This paper presents the design and performance of a passive compensation method that exploits a diaphragm valve. Thanks to its ease of integration, satisfactory performance and relatively low cost, this method could be a valuable solution to increasing the stiffness of aerostatic bearings. This work provides a procedure to design diaphragm valves depending on the type of the integrated pad and the desired nominal air gap height. Results demonstrate that, once correctly designed, the diaphragm valve makes it possible to obtain bearings with quasi-static infinite stiffness at the selected air gap height.

Numerical Analysis of the Diaphragm Valve Throttling Characteristics

The throttling characteristics of the diaphragm valve are numerically studied in this paper. Firstly, the diaphragm deformation performance is analyzed by a finite element method, while the upper boundary morphology of the internal flow field under different valve openings was obtained. Then the two-dimensional simulation of the weir diaphragm valve flow field is carried out in order to explore the optimal design of flow path profile. The study shows that the throttling characteristics can be improved by flatting the ridge side wall, widening the top of the ridge and gently flatting the internal protruding of the flow path. In addition, using the local grid encryption techniques based on velocity gradient adaptive and y+ adaptive can improve the accuracy of simulation results. Finally, a cavitation two-phase flow simulation is carried out. The results show that cavitation may occur below 50% opening of diaphragm valve in ultra-pure water system, which becomes more intense with the increase of inlet pressure and even leading to flow saturation on the micro-orifice state.