Working in the HVAC and Refrigeration industry there are many times when you are going to have applied torque when working on a particular job. In this blog, we help you understand the basics of torque and a method of applying torque. A bolt that has been over tightened can be just as disastrous as one that hasn't been tightened enough. A bolt that has been tightened beyond recommended torque specs can easily break in service.
Torque is measured as a unit of force acting on a rotating lever of some set length. North American made hex head cap screws have radial lines on their heads that indicate their tensile strength. When replacing a fastener, use a quality at least equal to or greater than the original fastener used on the machine. The more marks on the head, the higher the quality. Thus, bolts of the same diameter vary in strength and require a correspondingly different tightening torque or preload. Remembering that torque is the turning effort or force applied to the fastener to preload it, or place it in tension, and is normally expressed in inch-pounds (in.lb) or foot-pounds (ft.lb). A one pound weight or force applied to a lever arm one foot long exerts one foot-pound or twelve inch-pounds of torque. Note: Where possible always use OEM torque values which may differ from the table below.
SAE Bolt head markings
Maximum torque table
All torque values are expressed in ft.lb.
Method of applying torque
Always run fasteners up snug (do not over tighten) with a regular wrench and then observe the following four steps unless OEM instructions are available.
Run each fastener in the proper sequence up to 1/3 of their recommended torque setting.
Repeat the process running up to 2/3 of the required torque setting.
Repeat the process again, running every fastener up to full torque.
Repeat step #3 to be positive you have not missed a fastener.
For various HVAC and Refrigeration product information visit www.Parker.com/Sporlan.
Article contributed by Glen Steinkoenig, product manager, Contaminant Controls, Sporlan Division of Parker Hannifin.
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