42 MAY 2023 WorldWide Drilling Resource® Increase Production with the Mills Knife Perforator Adapted from Information by Mills Machine Company, Inc. The Mills Knife casing perforator is used to perforate pipe or casing by punching vertical slots through the casing wall. This tool is designed to cut through steel or PVC casing and requires a two-line rig. The main wireline holds the tool in the hole while plumbing black pipe is used to lower the knife into the hole and trip the perforator blade. The secondary line is a wireline or bailer line which supports the knife while the pulling rods are lifted. As the knife is lowered into the hole, the pulling rods are added by joint until the desired depth is reached. A location mark is made on the pipe to show the position of the punched hole. The rod is pulled up with a 3000-4000 pound force to extend the knife blade and pierce the pipe. The blade penetration of the steel is felt as a slight jerk through the rod. Lowering the rod releases the knife. The pipe is then rotated the desired degrees if a series of holes is required at that depth. It is recommended you practice near the surface to see and feel the operation of the knife before going downhole. Pulling too hard or pulling after penetration can split the pipe. After the perforations are made at the lowest level, the drilling rod is raised to the next desired level. This prevents fowling of the wireline. The top connection is a 2-inch NPT (national pipe thread) pin. The standard perforator is for 6-inch ID (inside diameter) casing with no more than .300-inch wall thickness. Backing shoes are also available to expand the 6-inch perforating knife to 8 or 10 inches. The 12-inch perforator can handle a .375-inch wall and also has backing shoes to expand out to 14 or 16 inches. Other sizes can be quoted upon request. The Mills Knife perforator is typically used in water wells. Once the casing is installed in the borehole, the Mills Knife is sent down the hole to cut perforations through the casing at water-bearing zones. It can be used at multiple depths and does not require any pump pressure as it is operated manually. The Mills Knife perforator in action. WTR
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