Why are my LPS load cell bolts breaking?

I have vessels and tanks with large mixers that are breaking the bolts on the Legacy HI LPS series load cells. Is there a problem with the installation or the bolts that could be causing this?

The bolts on the HI LPS Legacy series load cell supports the lower loading bracket for the load cell mount is a 3.5 inch long, grade 5 bolt. This bolt threads through the load cell. You can identify bolts of different grades by the markings on the bolt head. Grade 5 bolts have 4 marks on the head and have high tensile strength. The ultimate shear strength of a fastener is typically about 60% of its tensile strength.

The installation instructions specify the overall height of the load cell mount. This overall height limit is to reduce the space between the lower load bracket and the load cell body. The gap for a very active vessel should be 1/8" to no more than 1/4". Increasing this gap gives additional leverage to the tank and that bolt can break. The replacement bolt thread area must have the same as the original. Most off the shelf replacement bolts are not threaded sufficiently to allow the smaller gap between the lower load bracket and the load cell. You can order replacement bolts from Hardy Instruments or modify a new bolt in your shop to increase the length of the thread area. The thread area must be at least half the length of the bolt.

For tanks with extreme movement, check rod assemblies should be installed. Check rods limit the movement left and right and allow movement in the direction of desired weight change. See the attached power point presentation to learn more about check rods.