Hanger - Obsolete 1965 PDNHS Hanger
While hanger adjustment along the run of a pipe may not be too critical, it is important that the pipe weight is kept off isolated equipment in order to maintain alignment, protect cast flanges and flexible hoses. Should the piping weight fall on the equipment, the floor mountings become overloaded and inoperative. Back in 1965, we called for a type PDNHS hanger. This design did not have clearances as described in Specification D for the new 30N and our method of maintaining the elevation was to build the hanger with a firm platform above the spring and then to ask the contractor to follow the procedure of loading the spring and ultimately relieving this upper nut. This was very difficult to do, and in many cases it was not done at all, so the hangers remained solid hangers. While a theoretical specification may be convincing, we are all interested in performance so there was no point in continuing to call for a device that could not be adjusted properly.
Therefore, we changed the specification to call for the type PC30N as illustrated. Rather than a rigid secondary platform, we preload this hanger in our factory so that it is shipped with the rated deflection shown on the indicator. It remains a constant elevation device because the springs do not deflect additionally when the contractor adds the load. In order to make the hanger operative, he does not have to “wind up” the spring, but merely to release the spring by unlocking the nut at the bottom. If our assumed weight is incorrect, there will be a very minor upward movement as the spring assumes the exact load. While these hangers do not do the job as precisely as the old design, they are much less expensive to install and for all practical purposes the systems will be much better for our having made this change in our recommendations, as all hangers will be functional.
There is a strong need for these hangers near the equipment and that is the reason that we call for the first four hangers to be Type PC30N. They are also recommended for other situations, where you want a precise installation. They are particularly useful when hanging pipe that is 6 inches in diameter and larger, as they keep the pipe run level as the installation proceeds. When a contractor uses a standard hanger that deflects as pipe is added, it is very difficult to put large pipe in properly. In many cases, the contractor will install solid rods to begin with and then cut the rods and install the spring hangers later. This is a very expensive procedure that can be eliminated by using pre-compressed hangers throughout. It is a matter of economics.
In our specification, we call for this design for the first four hangers from the equipment (30 feet 9 meters). You can modify that requirement plus or minus should you edit our specification.
Hangers shall be as described in F, but they shall be precompressed and locked at the rated deflection by means of a steel precompression washer to keep the piping or equipment at a fixed elevation during installation. The hangers shall be designed with a release mechanism to free the spring after the installation is complete and the hanger is subjected to its full load. Deflection shall be clearly indicated by means of a scale. Submittals shall include a drawing of the hanger showing the 30° capability. Hangers shall be type PC30N as manufactured by Mason Industries, Inc.