What are these?

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Old 02-16-13, 03:08 PM
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Question What are these?

My guess is they are check valves but I'm not sure. This is on my .75" propane line.



 
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Old 02-16-13, 03:30 PM
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Unions. .
 
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Old 02-16-13, 03:54 PM
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As gilmorrie said, they are unions. When using threaded pipe, you can't join two different runs together because of the threads. This allows you to make that connection. It also allows an easy point to disconnect the piping.
 
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Old 02-16-13, 06:50 PM
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How do they differ from this type of connection?

 
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Old 02-16-13, 07:50 PM
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That second pic is a 'coupler' and only joins two lengths of pipe. Both ends are threaded.

The 'union' in your first pic (aka 'ground joint union') can be separated by loosening that locknut.

This pic shows one taken apart:


image courtesy weiku.com
 
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Old 02-16-13, 09:05 PM
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With a coupling at least one of the pipes need to be able to turn freely, that is not screwed into something else. A union can be used when neither pipe can be turned freely, that is both pipes are screwed into something else.
 
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Old 02-17-13, 10:15 AM
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Got it now, thanks. ............
 
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Old 02-17-13, 12:52 PM
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Best to browse the pipe-fitting department of a good hardware store. You will find - all sorted and labeled - tees, crosses, caps, plugs, nipples, street els, regular els, ball valves, boiler drain valves, gate valves, globe valves, hose bibs, and more. Their individual purposes are often obvious by inspection.
 
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