A chemigation valve is an apparatus designed to protect water supplies from agricultural chemicals used during chemigation, the application of chemicals such as fertilizers and pesticides through irrigation water. Most chemigation valves consist of a spring-loaded check valve, 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."