Wednesday, April 30, 2014

Do You Own a Backup Wrench?

I am often talking about new technology and recent trends in HVACR on this blog. Today I would like to discuss a rather old piece of technology – the backup wrench. If you work in mechanical trades and you don’t own a backup wrench, then you are my intended audience! A backup wrench is not used to reverse anything, and it does not have left handed threads. Backup wrenches are often specified by manufacturers when installing mechanical fittings, yet most techs do not have any wrenches in their tool box named a backup wrench. I have sometimes reminded students to use a backup wrench only to be told that they only have some open end wrenches and a couple of adjustable jaw wrenches – no backup wrenches. By now you hopefully have figured out I am pulling your leg. “Backup” does not describe a particular wrench, but how the wrench is used. The wrench is backing up the fixed part, keeping it from turning. When tightening a nut or fitting onto a valve or coil, you are often instructed to use a backup wrench. Many units have stickers on them stating: “use a backup wrench.” The backup wrench holds the fixed part in place, keeping it from twisting when the nut is tightened. Otherwise, it is quite possible to turn the fixed part once the nut is tight. This twists the copper tubing connected to the valve or coil connection, causing leaks and restrictions. Unfortunately, this is a common occurrence in school. Students try to “fix” a leaky flare with a 12” wrench and a hefty turn. Repairing the damage can be pretty tricky, and it is definitely time consuming. If you look carefully, most male flare connections have flats on them – that is where the backup wrench goes. One wrench goes on the fixed part and another goes on the part that is turning. That way you can control exactly what gets turned. So the next time you go to tighten a flare on a valve or coil, make sure to use a backup wrench. If you don’t have a backup wrench, send me $50 and I will send you one with instructions for using it.

1 comment:

  1. Carter

    Good advice. I may want to add to your content. Mueller brass and others recommend that a "line wrench" or more commonly called a flare nut wrench be used on flare nuts. The reason is that a wrench that only contacts 2 flats of a flare nut will cause it to be misshapen. When used on a low side of a system, as if on a TXV connection, this misshapen area will allow condensation to be allowed to freeze on the threads of the male connectors. This action will cause the flare nut to gradually turn out as the ice will continue to grow, revealing the mysterious leak to reappear. If a low side TXV leak continues to come back, have your students understand that the flare nut was installed incorrectly and it needs to be removed and replaced with a new one! I would change the flare nut on the first find of a leak to be safe.

    Best Regards