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Large enclosures: an open and shut case?

Large enclosures: an open and shut case? Gas struts can provide an ideal solution for holding open the lids and doors on larger sized enclosures.

Large cases and enclosures frequently have heavy lids and doors; from a user point of view this becomes an issue when the supported weight is too heavy for comfort, or when the weight is lighter but the frequency of opening is high, or the application requires a lid to remain open without support. In these situations gas struts offer an ideal solution in place of more traditional locking hinges as they are able to counteract part, or all, of the load from the lid, plus they are also far cheaper than other powered alternatives such as actuators or spring loaded return arms.

Until recently gas struts have been hampered by having a single fixed load rating. Different scenarios require different degrees of load to be taken by the gas strut, which can make specification difficult when choosing a suitable pressure, especially for single, variable or short-run applications. Manufacturers will fill struts with a bespoke gas pressure, but part costs or order numbers typically end up being very high relative to the product value. Fortunately adjustable gas struts are now available which allow users to tailor the product to their exact needs.

Large metal or composite enclosures are ideal for protecting valuable or delicate contents from external hazards, but when access is required it can prove extremely awkward to lift the lid and keep it open. Pioneered by the car industry for tailgates and often bonnets, in these situations a pressurised gas strut is ideal to share a degree of the required opening force against the lid to reduce the apparent weight for the user. Depending on the applications this may extend to supporting the entire weight or, in some cases which require self opening lids, slightly more.

Because the range of possible requirements is so large, and a pressure difference of just a few Newton metres can make a gas strut unfit for purpose, many suppliers are now supplying self adjusting gas struts which can be easily adjusted to suit individual requirements. Chris Putman, sales and marketing director at WDS, explains: "If you were to take a sample group of 100 applications where a gas strut was required to support an enclosure lid, I would happily bet that no two applications required the same force. Some applications require the gas strut to simply reduce the weight of the lid while other may require the lid to be held in place. In the first example the accuracy of the force isn't as critical so long as it does not exceed the closing force of the lid; however the second requires the exact closing force of the lid to be matched."

Application requirements
He continues: "Because there is such a wide range of possible pressure requirements it isn't possible to offer a complete range of pre-calibrated gas struts as standard without an unfeasibly large warehousing, or extended lead times. Stocking adjustable gas struts means that unit prices are low, and delivery times are short - typically next day from us, while product flexibility remains high."

Most adjustable gas struts on the market are extremely easy to calibrate, requiring a small allen key or screw driver to open a valve which releases pressure from the chamber. Once the first gas strut has been correctly calibrated it is easy to calculate the required force for the application by applying increasing loads to the gas strut until it begins to depress. It should be noted that, once released, pressure cannot be added so it is important to release the pressure slowly on a test sample.

Putman continues: "We have developed our product to be as user friendly as possible so you certainly don't have to be an engineer to use them. Firstly we supply an adjustment key with every product, meaning that no additional tools are required for calibration; secondly we can supply a simple equation to help users work out the required force for their application. "Where an OEM may require many gas struts to perform the same function then, once they have identified the ideal pressure for their application, we are able to supply them with fixed pressure products which have be pre-loaded with the correct force. The products in our range are able to supply forces of between 20Nm and 2,500Nm, we use high quality materials for the adjusting valve and seals to ensure that constant and precise pressure is main-tained once adjustment in complete."
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