I appreciate the comments. The body of my post describes the product (as presented on the cut sheet) as a wedge action restraint. Probably should not have used the set screw language in the subject line – that shows my unfamiliarity with these products. My concern is with the vibration associated with the diesel drive.
Bill Brooks From: Sprinklerforum [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, December 19, 2016 11:03 AM To: [email protected] Subject: RE: Use of Set Screw Type Restraint Fire Pump Suction and Discharge Mr. Brooks appears to describe two differently designed products. In his subject like he uses the words “Set Screw Type”. But, in the body he describes a “wedge action restraint”. Some products use set screws to retain the pipe’s axial position in a flanged joint. Some products use set screws for this same purpose in mechanical joints. The set screws exerts compressional or clamping force cutting a small pocket on the outer surface of the pipe wall. The screw tips are in shear when thrust bears on the joint. This type of restraint can be successful at keeping the joint together when only exposed to internal pressure fluctuations. But, it is not suitable if the joint is exposed to vibrations such as is produced by a diesel engine driven fire pump. The “wedge action restraint” appears to describe the design of products like Ebaa Iron’s Megalug or Romac’s RomaGrip. The bolts are fitted with wedge teeth tips that penetrate the outer pipe wall. Under load the teeth form a buttress of cold formed pipe material. As the load increases, the buttress increases transferring the load longitudinally along the pipe without affecting the design thickness of the pipe. These have been tested under severe cyclic loads and the wedge impressions look the same as if a single non-cyclical test had been performed. If exposed to vibrations, it would appear that this design would perform better than the simple set screw; however, I don’t know if such testing has been conducted. J. Scott Mitchell, PE Senior Fire Protection Engineer Mission Engineering CNS Y-12 | 865-576-5258 CNS PTX | 806-477-5883 On Dec 16, 2016, at 6:20 AM, Bill Brooks <[email protected] <mailto:[email protected]> > wrote: A case came up today about the use of a “mechanical joint wedge action restraint” on the suction and discharge side of a diesel driven pump. Someone accepted a change and eliminated the rods, then put a MJWAC at the top of the ductile pipe on each side of the pump. A commissioning agent has refused to start the pump based on the concern the restraint will “wiggle” off the end of the ductile under repeated pump operation either during the acceptance test or sometime later. Is this a creative use of this type restraint, or is it a totally bad idea? By the way, the underground elbow is a restrained type mechanical joint. Thanks Bill Brooks Brooks Fire Protection Engineering Inc.
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