## Why You Need a Torque Wrench (or Two…)

I’ve got a confession to make.

I'm “that guy.” Call it OCD, call it being anal-retentive, but I'm always making an effort to be as technically correct as possible. One aspect of that effort has been the use of torque indicating or torque limiting tools when tightening fasteners.

It started after I put new valve plates and gaskets on a Carlyle 06E compressor. As I was always taught, all the torque you needed to apply to a fastener was the torque you could apply with a normal-sized combination wrench. So, that is exactly what I did. The compressor gaskets failed and were bypassing the very next day because I didn't get those bolts tight enough. The tech who took that call asked me if I had and used a torque wrench. At first, I didn't understand.. Sure, I tightened the bolts. No, he asked, did you TORQUE them to specifications? 90-100 ft/lbs was the spec and, while you can get that kind of torque out of a standard length ¾” wrench, you're working at it.

That question started a dive down something of a ‘rabbit hole’ for me, and I'm going to share some of what I learned.

I started with one torque wrench, which I used just to tighten the bolts on compressor heads. From there, I've expanded to have three torque wrenches (¼, ⅜, and ½ drive) and a torque limiting screwdriver, mostly for electrical connections.

What is torque? Simply put, torque is a measurement of the amount of force required to turn a fastener. For bolts, torque is normally measured in ft/lbs or in/lbs. To help you understand, those are foot-pounds (ft/lb) or inch-pounds (in/lb). A foot-pound is one pound of force applied on a lever one foot long measured from the center of the fastener.

As we continue to increase the torque applied to a bolt, the male threads on the bolt move deeper into the female threaded hole while the part being fastened, a compressor head, for example, prevents the head of the fastener from following them. This stress results in a stretching of the bolt. That stretch applies what is called ‘clamping force’ to the assembly. This stretching permanently deforms and weakens the bolts, and sometimes proper assembly requires new bolts. Lubricant applied to the fastener makes it easier to turn, which decreases the torque required to achieve the same clamping force. Be careful always to follow manufacturer guidelines.

One place where torque wrenches are making inroads in our industry is with ductless mini-splits. While I haven't broken down and added one of these to my kit yet, I do have an easy way to torque flare fasteners using a regular torque wrench: crowfoot wrenches.

These little guys allow you to turn any ratchet or breaker bar into a handy wrench. To use them with a torque wrench, however, requires a little extra step.
Remember how we measure torque? It's based on the distance between the center of the fastener to the point where force is applied. Well, a torque wrench is calibrated to have force applied on the knurled part of the wrench handle and centers that force on the centerline of the drive spindle. Adding a crowfoot wrench to the end of the wrench changes the center of the applied force. We need to account for the extra length of the crowfoot and the extra leverage that it creates.

For this, use your required torque force as TA to solve the math. That said, I've found very little actual difference when using a crowfoot wrench, and since often torque values are given in a range, it isn't really necessary to calculate the difference,. Just set your wrench to the low end of the torque range and use the crowfoot. That will generally keep you within the specified torque range.

Another trick, where possible, is to install the crowfoot at a 90° angle to the drive. Doing this makes the actual and effective length of the tool the same and allows direct use of the tool without calculations. Keep in mind that a standard socket drive extension won't affect your torque wrench settings because it doesn't affect the length of the tool in the direction that matters.

I hear a lot of guys argue against using a torque wrench because they can tighten things up just fine without one. Probably so. I did a lot of jobs prior to the one I mentioned earlier without using one, and I was “just fine…” or was I? Did I tighten those flanges evenly, or did I warp the flange by over-torquing one side? Did I over-torque that flare and set myself up for a leak later? Did I tighten all the bolts evenly, ensuring even clamping force on all those gaskets? A torque tool simplifies things for us. Tighten to the specified torque, and you're done. You don't have to think about that variable anymore. It's as tight as it's supposed to be and no tighter.
It's one less thing to worry about.

—Jeremy Smith

## Related Tech Tips

Sometimes, Experience Can Hold You Back
When working in a business with people, you have two options: 1. Become bitter as you experience people, life, and issues. 2. Grow from experiencing people, life, and issues. I’m not proud to say it, but I realize now that when I started my business and had bad experiences, I would run to option #1 […]
The Case For Pulling The Blower Housing
When I started in the trade in 1999, there were still many oilable blower motors in service. As part of the maintenance, we would remove the housing and oil the motor. We would also vacuum the motor and wipe it down. As oilable motors have become extinct, I see fewer and fewer techs pulling the […]
Can You Discharge a Capacitor Using a Voltmeter?
I got a lot of comments that many of you discharge run capacitors with a voltmeter. I test this method vs. the capacitor discharge tool I created. Obviously, many of you use needle nose pliers or a screwdriver. While this is widely practiced, it could result in an arc, shock, or damage to the capacitor. […]

### 5 responses to “Why You Need a Torque Wrench (or Two…)”

1. Hello Bryan Orr,
I read your whole post and it’s really so informative. A torque wrench is a tool used to apply precisely a specific torque to a fastener such as a nut or … This standard covers the construction and calibration of hand operated torque tools. Seriously thank you for all this awesomeness.
Thanks for sharing such a valuable post and Keep Posting!

2. Francisca Sanders says:

I only ever use a torque wrench for engine rebuilds. For people who have got the limited budget, they should choose CDI torque tool. Because it is one of the best quality product with cheaper price than Snap-on torque products.

3. alan ceil says:

This is a very beautiful and clear article. If anybody read this article properly then he must get help from this article. Thank you for shear a great article. Really this article has details a torque wrench.

• HVAC School says:

You’re welcome. Glad to hear it!

This site uses Akismet to reduce spam. Learn how your comment data is processed.