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Guidelines for Municipal Chemical Injection
“The Fundamentals of Municipal Chemical Injection Begin with Safety”
Safety is the most important issue to consider when choosing or working with chemical injection quills. The goal of chemical injection is to inject a chemical solution into a water main through an injection quill or chemical injector. Process flow, pressure within the water main, and the chemical solution are important factors to consider when choosing a chemical injection quill. They also have the greatest impact on operator safety.
Chemical Solution: Chemical solutions are commonly used in water & wastewater treatment. The chemical solution is injected 1/3 to 1/2 the diameter of the water main where velocities are the highest and away from the sidewall. Some chemical solutions used in municipal water treatment are corrosive to piping and equipment. Caution must be used when selecting an injection quill material for use with corrosive chemical solutions.
Pressure: Most water mains are pressurized. Since the injection quill is connected to the water main, it is exposed to maximum pressure and surge conditions associated with the water main.
Process Flow: Moving water pushes against the solution tube as a lateral force. The faster the water is moving and the farther the solution tube is inserted into the water main, the greater the force against it. Control valves, elbows, and bends in the piping system create turbulence disturbing the laminar flow pattern.
Retractable Injection Quill
Retractable injection quills are the most common type of injection quill for municipal chemical injection. The two main assemblies which make up a retractable injection quill are the ball valve (corp. stop) and solution tube. The solution tube connects to the chemical feed line, which then feeds the chemical solution into the center of the water main. An adequate restraint system and choice of material for the solution tube are critical to the safe operation of this unit.
Restraint System for Retractable Injection Quills
The solution tube feeds the chemical solution into the center of the water main. It must be made from a material which is compatible with the chemical solution.
PVC, CPVC, & PVDF (Kynar®) Solution Tubes
Metallic Solution Tubes
Non-Retractable Injection Quill
Typically used for injecting a low volume of chemical solution. You cannot safely remove a non-retractable injection quill from a pressurized water main with moving water. Moving water must be stopped, pressure relieved and water drained to a level below the injection quill before removing the quill from the water main.
Connecting the Chemical Feed Line to the Injection Quill
Full rigid piping to the injection quill, rigid pipe transition to flexible hose, and flexible tubing are all acceptable methods for connecting the chemical feed line to the injection quill. Flexible hose or tubing, when installed with a loop, will allow the operator to remove the solution tube without breaking down the chemical feed line.
Connecting the Injection Quill to the Water Main
A Half Coupling, Direct Tap, Tapping Saddle, or Riser flange are all acceptable ways to connect the injection quill to the water main.
Solution Tube Tip Configurations
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