Process Equipment Update


exhaust side of the pneumatic system, they are exposed to sudden shock loading, meaning their oil removal capabilities are not as good as those using coalescing filters. A good exhaust silencer, however, should remove oil to around typically 2 ppm under average usage conditions.


Protection device selection Firstly, decide which parts of the system cannot withstand the maximum pressure which can be developed in the distribution system (or compressor). Then, determine which type of relief valve is required to control this air pressure most effectively, taking into account failure flow through that part of the system. Consider using a restrictor (orifice) without producing excessive pressure losses in the normal operation of that part of the system to enable a suitable size of relief valve to be used. For very large flows consider a pilot operated


regulator as a dump valve, with a diaphragm relief valve pilot. For machines consider an in-line device to build-up


one complete integral modular preparation assembly for ease of piping, location and servicing. Decide which parts of the system can suffer from


problems on initial start up, or resetting where excessive initial speeds can lead to wear problems or entrapment, or where an emergency stop/dump function is required. Employ one soft start/dump valve for each section


of the system operated in this way. The larger the system the longer the dump or emergency stop function will take to fully empty the system. If there is a high safety risk in this part of the machine consider monitored soft start/dump versions along with


appropriate other circuitry to comply with the machinery directive. Locate soft start/ dump valves in the FRL assembly closest to the downstream end to prevent high back flows through the lubricator. Where large


volumes of air are to be exhausted consider fitting a silencer if the air cannot be piped away to a convenient position. Where rapid cycling of exhaust is present fit a heavy duty silencer. Where the exhaust air can be heavily laden with lubricant, usually from equipment requiring high levels of lubrication, fit a coalescing exhaust silencer.


Other products In addition to the products and devices described above, there are other air line products that can be used to help increase the level of safety in pneumatic systems. These include preset pressure regulators, lockable shut-off valves, and tamper resistant kits. n


Fig. 4. Pressure relief valves protect compressed air systems from over-pressurisation.


Ben Rickards is Product Technical Manager with Norgren, Lichfield, Staffordshire, UK. www.norgren.com/uk/industrialautomation


Electric industrial heaters for explosion hazard areas


E


lectric heaters with explosion hazard area approval are demanded by many branches of the chemical and


petro-chemical industry. Through advanced development of its products for use in explosion hazard areas, Hillesheim has obtained certifications for its own prototype tests. These certifications ease the burden for customers because it is no longer necessary to have


on-site approval inspections performed by appraisers. These costly and time-consuming tests at the customer site can now be waived in the future.


Hillesheim manufactures explosion- proof heating hoses for media that must be held at temperature (up to 200°C) while being transported from A to B. Depending on hose type, these hoses can be used in temperature classes T1 ... T6, for gas


zones 1 and 2 and for dust zone 21/22. Other products, such as heater bands and heating plates, are also deliverable for use in explosion hazard areas. Hillesheim is hoping these new developments will open up new applications for the analysis of smoke and emissions as well as in general plant engineering for explosion hazard areas. n


For more information ✔ at www.engineerlive.com/epe


Hillesheim GmbH is based in Waghäusel, Germany. www.hillesheim-gmbh.com


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