A chemigation valve is an apparatus designed to protect water supplies from agricultural chemicals used during chemigation, the application of chemicals such as fertilizer

Fertilizer

Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...

s and pesticide

Pesticide

Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s through irrigation

Irrigation

Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

 water. Most chemigation valves consist of a spring-loaded check valve

Check valve

A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....

, a low pressure drain, an air and vacuum relief valve, and an injection port for introducing the chemicals downstream of the check valve. Many chemigation valves also have a 4 inch inspection port so that a person can reach inside and feel if the check valve is still functional. Some governments require the use of two chemigation valves installed in series if hazardous chemicals are to be injected.

Texas State law Chapter 344.73 in Subchapter D - 1.(b)
"An irrigation system which adds any chemical is considered to be a 'high health hazard'. Such an irrigation system must not be connected to any potable water supply except through a reduced pressure principle backflow prevention assembly."

See also

• Air gap
• Hydrostatic loop
  Hydrostatic loop
  A hydrostatic loop, though not often used in plumbing practice, is an arrangement of pipes formed into a vertical loop to prevent backflow of water within the plumbing potable water system. Since a siphon has a maximum height that it can work , a hydrostatic loop is built higher than 33 feet...
  
  
• Pressure vacuum breaker
  Pressure vacuum breaker
  A Pressure Vacuum Breaker is a type of backflow prevention device, used to keep non-potable water from entering the water supply. A PVB is similar to an atmospheric vacuum breaker , except that the PVB contains a spring-loaded poppet. This makes it acceptable for applications that are high...
  
  
• Double check valve
  Double check valve
  A double check valve or double check assembly is a backflow prevention device designed to protect water supplies from contamination. It is also a valve used in air brake systems on heavy trucks.Usage in Water Supply:...
  
  
• Reduced Pressure Principle BFP
• Atmospheric vacuum breaker
  Atmospheric vacuum breaker
  An Atmospheric Vacuum Breaker is a backflow prevention device used in plumbing to prevent backflow of non-potable liquids into the drinking water system. It is usually constructed of brass and resembles a 90-degree elbow with a hood on its top to allow air to enter the water system if a siphon...