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world of industries 8/2016 (EN)

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world of industries 8/2016 (EN)

Diffusers to the rescue

Diffusers to the rescue MDA INDIA For operational issues like fluid aeration, foaming and noise arising in the hydraulic systems, hydraulic accessories like diffusers, return line filters and breathers offer simplistic yet effective solutions. About Stauff The company Walter Stauffenberg Co & KG, located in Werdohl in Germany‘s Sauerland region, is now an internationally leading developer, manufacturer and supplier of hydraulic systems and components, pipework equipment under the brand name Stauff. The company has a comprehensive range of products which includes clamps, filtration technology, diagtronics, hydraulic accessories, valves and tube fittings. Hydraulic accessories includes fluid level and temperature indicators, tank filler breathers, suction line accessories and filter line accessories, pipe tube and hose cleaning systems. Stauff is represented by a tight network of distributors and wholly-owned manufacturing facilities, distribution bases and warehouses in 18 countries worldwide. One of the basic pre-requisites for the smooth operation of hydraulic systems is the selection of a well-designed hydraulic reservoir based on the application requirements. Traditionally the function of the hydraulic reservoir is to supply the system with sufficient fluid at specified pressures that vary according to the system’s needs. Today’s reservoirs are much more than just storage tanks for pressurized fluid, as they designed also to provide a surface area for transfer of heat from the fluid to the surrounding environment. The size of the reservoir is designed by also considering the volume required to let the returning fluid slowdown from a high entrance velocity. This also lets the heavier contaminants settle and the entrained air to escape. An ideally sized reservoir provides a considerable air space above the fluid to accept the air that bubbles out of the fluid, space for hot-fluid expansion, gravity drain-back from a system during shutdown, and storage of large volumes needed intermittently during peak periods of an operating cycle. A physical barrier or a baffle is provided to separate the fluid entering the reservoir from the pump suction line. While designing the hydraulic reservoir an access to remove used fluid and contaminants from the system and to add new fluid is also thought about. While designing, suitable measures such as filler breathers and sufficient tank pressurisation are also taken to prevent solids, water and air from entering the system, contaminating the oil and affecting the function of sensitive components, which quite often results in expensive downtimes and unplanned oil changes. Undesirable foaming Another factor that should not be underestimated is surface foaming which can form through uncontrolled return flow of hydraulic oil from the return line into the tank. Foam is a collection of small 30 World of Industries 8/2016

MACHINE ELEMENTS bubbles of air that accumulate on or near the surface of the fluid. As an air-in-oil dispersion, this can cause a number of operating problems throughout the system. In severe cases, the foam can leak out of the machine through breathers and sight glasses. Foam is an efficient thermal insulator, so the temperature of the oil can become difficult to control. This can cause efficiency losses for the energy used, operational malfunctions and a reduced service life of the oil. The presence of air bubbles in the fluid can lead to excessive oxidation, cavitation, the reduction of lubricating properties of the oil and hydraulic system failure. Cavitation in the pump also increases noise generation in the system drastically, which in extreme cases can lead to a total breakdown and therefore to a system standstill. Diffusers to the rescue Diffusers effectively reduce the aeration, foaming, turbulence and noise caused by return lines. Reservoirs, baffles, and return lines should be designed to prevent the formation of foam and bubbles. But for added protection, a diffuser can be positioned near return lines to break up foam bubbles as they enter the reservoir. The German company Stauff manufactures diffusers along with various other hydraulic products and systems. The design of its SRV series diffusers is based on two concentric steel tubes where the perforated outlet sections are offset to each other. Due to the offset in the 2 concentric steel tubes the oil in the return flow slows down and effectively settles down. This prevents the formation of oil foam and permanently reduce noise generated in hydraulic reservoirs. It also effectively prevents the raising of sedimentation and soil deposits from the bottom of smaller tanks. Diffusers are an ideal supplement to return-line filters with threaded outlets. They are connected directly to the return line or to the filter bowl of the filter housing using BSP or NPT internal threads. The diffusers are positioned fully 01 Diffusers from SRV series 02 Return line filter from SRV series underneath the minimum liquid level of the reservoir, ideally with the closed surface of the outer steel tube facing the suction end of the pump. Flow diffusers are becoming more popular as reservoirs become smaller. In the past, large reservoirs were specified to provide plenty of time for entrained air to rise to the fluid surface. With smaller reservoirs, however, fluid spends less time in the reservoir, so there is less time for air to rise to the surface. Stauff’s extensive product range offers diffusers for a maximum operating pressure up to 20 bar (in the return line) and the operating temperature range of – 20 to + 100 °C, covering the complete spectrum of required flow rates up to 950 l/min. Photographs: Walter Stauffenberg GmbH & Co. KG 03 Open reservoir with oil foam World of Industries 8/2016 31