What Can Result in Increasing Length and Constant of Compression Springs?

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miladbrain Participant Join Date: Aug 2018 Posts: 3	What Can Result in Increasing Length and Constant of Compression Springs? 07/18/2019 12:10 PM
	In a part that controls the flow rate, there is an evacuated bellows (a metal bellows with a spring embedded inside). With increasing pressure, the bellows is compressed and more flow passes and without pressure, bellows realxes at its initial length. Recently, we've faced failure in a number of these parts. After tearing down, we noticed that the bellows has lengthen and its constant has increased considerably. That's why it didn't pass any flow at defined pressures. This failure happens to part after several months of operation. This part is exposed to cyclic temperatures from room temperature to an elevated temperature of about 160 C. Can thermal shock besides cyclic load result in increasing length and constant of compression springs? [unfortunately I have no information about bellows and inside spring material]
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Rixter Guru Join Date: Apr 2010 Location: About 4000 miles from the center of the earth (+/-100 mi) Posts: 9911 Good Answers: 1141	#1 Re: What can result in increasing length and constant of compression springs? 07/18/2019 12:38 PM
	My wild guess is that maybe gas has leaked into the evacuated bellows... Here are some other ideas... https://www.valvemagazine.com/magazine/sections/maintenance-repair/4438-common-bellows-failures-and-suggestions-for-mitigation.html
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SolarEagle Guru Join Date: Mar 2007 Location: by the beach in Florida Posts: 33392 Good Answers: 1817	#2 Re: What can result in increasing length and constant of compression springs? 07/18/2019 12:57 PM
	Without a detailed forensic investigation and spec sheet on valves, as well as the fluid specs and operating parameters, we can only guess... __________________ All living things seek to control their own destiny....this is the purpose of life
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#3 Re: What Can Result in Increasing Length and Constant of Compression Springs? 07/18/2019 2:44 PM
	A schedule needs to be prepared for assessment by the valve manufacturer or, if they were ordered from a valve distributor, the distributor on the valve manufacturer's behalf. The schedule needs to include: sizes, part numbers, wetting agent, wetted materials, flowrates, temperatures and pressures as a minimum. The recipient can then make an assessment and make educated recommendations in the way that this forum never could. That's quite a lot of homework. Go for it. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#4 Re: What Can Result in Increasing Length and Constant of Compression Springs? 07/18/2019 3:24 PM
	If in doubt, replace it. The bellows are not to spec, I think, if it was spec'd in the procurement documents. Bring things back into control and then investigate.
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dkwarner Guru Join Date: May 2006 Location: Placerville, CA (38° 45N, 120° 47'W) Posts: 6215 Good Answers: 248	#5 Re: What Can Result in Increasing Length and Constant of Compression Springs? 07/18/2019 10:40 PM
	One possibility is work hardening of the bellows and/or the spring. __________________ Teaching is a great experience, but there is no better teacher than experience.
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Stef Guru Join Date: May 2018 Location: Under the spreading Bunya Trees, South Burnett, Queensland, Australia Posts: 807 Good Answers: 65	#6 Re: What Can Result in Increasing Length and Constant of Compression Springs? 07/19/2019 12:28 AM
	I would suspect the bellows has softened and lost its elasticity allowing the spring to extend its length. Check the suitability of the bellows material for the task and if any temperature excursions above normal temperature have occurred which could have impacted on the bellows. __________________ Hare today, goon tomorrow!
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dkwarner (1); lyn (1); PWSlack (1); Rixter (1); SolarEagle (1); Stef (1)

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