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.
- Designed for insertion and extraction of the solution tube while in service and under system pressure.
- Know how fast the water is moving and how much pressure is in the water main before withdrawing the solution tube
from the water main.
- Read the manufacturer’s instructions and guidelines before withdrawing a solution tube from a retractable
injection quill when under pressure.
Restraint System for Retractable Injection Quills
- The restraint system holds the solution tube in place when in service and prevents it from being withdrawn while under pressure.
- The restraint system must be capable of holding the solution tube securely in place when subject to maximum system pressure and/or surge conditions.
- The compression seal, or “packing gland” is not a not an acceptable restraint system. This component is designed to
be just hand tight to cut off any seepage. Rarely will a wrench be required.
- The Restraint system must have a pressure rating. The recommended margin of safety for the restraint system should be 250% of maximum operating pressure.
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
- These are the most common materials for municipal chemical injection.
- Keep the insertion lengths short. We suggest no longer than 6 inches.
- Know how fast the water is moving and avoid areas of turbulence before using them.
- Avoid using them when feeding corrosive chemical solutions into the center of large diameter mains.
Metallic Solution Tubes
- Mettalic solution tubes are the best choice for retractable and non-retractable injection quills.
- Stainless Steel, Titanium Grade 2, Alloy 20 and Hastelloy® C-276 are the best material for solution tubes. They will easily handle all chemicals
used in water & wastewater treatment. They won't have the potential to bend or break like solution tubes made from PVC, CPVC, or PVDF (Kynar®).
- Chemical solutions corrosive to water mains should be injected into the center of the water main.
- Chemical feed point should be in the center of the water main. This is where velocity is highest.
- Make sure the solution tube material is compatible with the chemical solution.
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
- Standard Tip: The chemical solution exits the “downstream” side of the tip and releases not at the tip, but at some other point away from the tip.
- 45 Degree Bevel: Chemical solution is released “facing” the flow of water which causes instant dilution of the chemical solution.
Not recommended when injecting sulfuric acid or chemical solutions prone to clogging.
- Saf-T-Seal: Reduces the chemical solution from mixing “inside” the solution tube. This tip helps reduce or
eliminate tip clogging which is common with some chemical solutions.
- The placement of the injection quill on the water main can vary. The most common position is vertical or horizontal. The injection quill will function properly in any position. The exception is when a “floating ball” check valve is attached to the solution tube. In which case you want the installation to be at the bottom 4:00 or 7:00 o’clock position.
- A horizontal installation is recommended. If a leak does occur anywhere on the chemical feed line, the chemical solution won’t leak onto the injection quill and water main. It is also easier to work with an injection quill installed in the horizontal position.
- A check valve is not recommended when injecting a gas solution
- The check valve prevents water from entering the chemical feed
system. It should be placed as close to the injection quill as possible.
- A “spring loaded” ball check valve is recommended over the
“floating ball” type of check valve.