What does a double check valve do?

The DCV operates with a series of spring-loaded check valves that allow water to pass through one way but not the other way (in other words, not backward—thus “backflow prevention”). A DCV is a safety device in many ways, like a properly working vacuum breaker on a hose spigot but more robust.

The DCV also has two pretty important shut-off valves that must be properly functioning. By functioning, we mean that the handles have to be present (not rusted off or partially missing), easily accessible (not covered with years of mud washout and dirt), and not frozen in the open position with rust buildup. The issues noted are very common because this valve is hidden from view and rarely used. In fact, the majority of homeowners don’t know about it at all.

A properly installed and properly functioning DCV allows for safety testing and water leak testing. And if the water to your irrigation system ever needs to be turned off, the DCV is the only shut-off valve for that purpose. Anyone who has had an irrigation valve malfunction or get stuck in the open position knows how important these two handles are.

Most people don’t know what a properly installed DCV is supposed to look like because builders never install them correctly, and irrigators rarely do. They also use inferior materials that will prematurely fail.

Here is what it should look like. When you open the lid of the valve box, the DCV should be completely exposed and clear of any dirt, mud, or debris. In fact, the valve box should not have ANY dirt or mud accumulation inside at all. You should be able to see the black plastic on all 4 sides all the way to the bottom of the box.

Although it is not required by code like it is for the Pressure Reducing Valve (PRV), we always pack the bottom of our valve boxes with 3-6 inches of pea gravel. Adding this pea gravel allows for better drainage and keeps the mud build-up down to a minimum for a longer period of time.

All of our trucks carry 60 to 80 pounds of pea gravel because technically, it is a plumbing-required item. And of course, we have both of the most common sizes of DCVs on every truck.