drives & controls - Industrial Technology Magazine

MECHANICAL COMPONENTSSprings, Gas Springs & DampersGas springsflying highJet Press’s gas springs give watchers abird’s eye view of endangered eaglesThey are usually employed to hold open car boots orprop up heavy covers allowing access toindustrial machinery, but gas springs haveproved they can have a softer side by allowingenthusiasts to get closer to one of the country’srarest birds. Six Camloc gas springs have beenpurchased by the Forestry Commission Scotland andfitted to a bird hide which will allow dozens of watchersan unobstructed view of magnificent white-tailed seaeagles in their natural habitat.The hide, operated under the Mull Eagle Watchpartnership, is the only organised hide in the world tooffer a view of a white-tailed sea eagle nest, and issituated on the banks of Loch Frisa in a remote area of theIsle of Mull. It has canvas interpretation panels and twoTV screens featuring live footage of the eagles, the UK’slargest and most endangered birds of prey, which isbeamed into the hide from CCTV cameras placed close tothe nest. However, earlier this year, the Commission got intouch with industrial components suppliers Jet Press,based in Huthwaite, Nottinghamshire, with a challenge.At the front of the hide are three wide windows, whicheach weigh 6kg and are hinged so that they can beopened to allow watchers to rest their elbows on thewindow frame and look through their binoculars.However, weather in Mull is changeable. The Commissionwanted a mechanism whereby not only could thewindows be held open securely on windy days so thatthey would not shut or twist, they also had to be closedeasily, safely and quickly by rangers at the hide, which isa walk and a minibus ride away from where the visitorspark their cars. The task to find a suitable solution fell toForestry Commission buildingsurveyor Steve Wassall, whodecided that what was needed wasa set-up similar to an open car boot.He realised that he needed two gas springs for eachwindow, but was unsure of what specification they wouldhave to be. He approached Jet Press and outlined theproblem to its technical manager, Martin Belcher who,given the remoteness of the site, would have to doeverything over the phone.Jet Press stocks gas springs manufactured byArvinMeritor in Leicester and its range reflects the vastversatility the motion control components offer in size,performance capabilities and their applications. “Gassprings are used for an incredible number of differentapplications, but this was certainly a new one to us,” saysBelcher. “They are, however, perfect for the job, althoughthe application required some communication betweenSteve and myself to establish the type of strut and themounting point positions to achieve the required action.”After getting Wassall to weigh and measure thewindows, Belcher worked out what was needed. “Therange of gas springs we stock can handle lid weights from5kg up to 250kg, and we can normally calculate the gasspring force required to suit the application,” he says.“But small changes in the centre of gravity,temperature or the mounting position canradically alter the handling characteristics of thegas strut. Add to this the changeable weatherconditions in the Mull, and calculating the optimum gaspressure for the strut soon becomes analmost impossible task.” In the end, Belcherdecided that the task would be best servedby using a Varilift gas strut in the 8-18range. The Varilift has a gas release valvewhich would allow the fitters to release smallamounts of gas from the strut until thecorrect ‘feel’ of the gas strut is achieved.“Another consideration was the need to openthe windows safely,” Belcher continues.“After all, we did not want the window tospring open as soon as the catch was released, as thiscould cause injury to anyone stood nearby.”This involved accurately working out the static anddynamic mounting points so that the window had a slightself closing action over the final 5 to 10 degrees ofmovement, whilst still keeping them in an achievableposition for the frame and window constraints. Thissolved one problem. Next, Belcher had to consider thepossibility that the weather could cause the window toslam shut in a gust of wind. “Also, the sensitive nature ofthe birds means that there is always a ranger present, butat the end of the day, they are often alone, so one personneeds to be able to close the windows,” says Wassall.“Because of the size of the windows, it would beimpossible for them to reach and activate the lockingmechanism on the gas struts on both sides of the windowat the same time as closing the window.”Belcher comments: “These problems forced us toconsider the Econoloc range, which has a locking shroudwhich springs into place once the gas strut has reachedits full extension. It acts like a mechanical lock, preventingclosure of the window without manually releasing thelocking shroud.” After a flurry of telephone calls andpaperwork between Nottinghamshire and Scotland, theproblem was solved. The hide has one Econoloc strutfitted on one side of the window and a Varilift Swift andSure on the other, which allows one ranger to operate thelocking mechanism with one hand and close the windowwith the other.The springs were sent to Mull in February, allowingWassall to fit them well in time for when the eggshatched – allowing the watchers to enjoy natureunfolding before them. All of this went unnoticed to theeagles themselves, but has made a significant differenceto the enthusiasts watching the birds. “We are delightedto have solved the problem,” says Wassall, “especiallysince we were not able to see the hide at first hand. Wehope that the gas springs add, if only in a small way, toeverybody’s enjoyment of watching the sea eagles intheir natural habitat.”MORE INFORMATION:Enter J465 on the enquiry card, or visit ‘latest issue stories’www.industrialtechnology.co.uk for further details from Jet Press andmore stories on springs, gas springs and dampers46INDUSTRIAL TECHNOLOGY • October 2008