Backflow Preventer


Backflow Preventer

Backflow Preventer

DIG 3/4″ plastic backflow preventer is an attachment commonly placed into the faucet when used with drip irrigation to keep contaminated water from being siphoned backward into the household water supply lines. The backflow device is an economical way to eliminate the risk of water contamination from dirt or fertilizer back-flowing into the water supply through an outdoor faucet. A backflow preventer is highly recommended when installing a drip system.

Special Features:

  • Easy to install
  • Available with 3/4” female hose thread to fit all standard hose thread connections
  • Keeps contaminated water from entering the household water supply
  • Provides protection from back flow and back siphoning of water
  • Compact construction of non-corrosive plastic materials
  • Low pressure loss and high flow rate


How to Order
D45 Backflow Preventer Inlet 3/4 in. FHT x Outlet 3/4 in. MHT


  • Operating pressure: up to 100 PSI
  • Flow rate: up to 8 GPM
  • Size: 3/4” female hose thread x 3/4” male hose thread (3/4” FHT x 3/4” MHT)
  • Color: black
  • Temperature range: up to 130°F
  • Materials:
    • Body: high impact plastic
  • DIG Drip Zone Head Assembly: Connecting to a Faucet


The backflow device (vacuum breaker), when used in a drip irrigation installation, is installed after the faucet or hose bib. If used with a hose end timer, the backflow device is installed after the controller to lower the stress of braking on the backflow device. A backflow preventer should always be used when applying fertilizer through a drip irrigation system to prevent backflow of non-potable or contaminated water into the main water supply line.
The backflow operation depends on water pressure. When the water supply turns on, the backflow device seals off the atmospheric vents and allows water to flow downstream. When the water turns off or a pressure loss accrues in the supply line, the backflow device seals the water passage and the vents open, allowing air into the system or water backflow to flow out. The backflow device’s main feature is to prevent irrigation water from re-entering the water supply line. In other words, a backflow device acts as a one-way valve, allowing water to move in one direction only and prevents back siphoning of non-potable water into the water supply line.

Backflow of water may be caused by conditions such as an elevated irrigation system, when the downstream pressure is greater than the supply pressure, breakage of pipe in the water supply line forming vacuum conditions, and when there is negative or sub atmospheric pressure downstream through the irrigation laterals.

Note: Some municipalities and local water districts require the use of backflow device/atmospheric vacuum breakers, so to meet these regulation requirements a backflow device or anti-siphon valve must be used. The backflow device (vacuum breaker) DIG provides cannot be used under continuous pressure. The city codes related to this device do not permit using it under continuous pressure as it can stop functioning in emergency conditions. If used under constant pressure, this backflow device can crack and fail due to a pressure surge when the downstream valves close. Make sure to check your local city code to see if this device is required.

Installation suggestions

The point of connection to the water supply can start from a faucet (hose bib), valve, well, pump or rain barrel combined with gravity feed.

Installation into a faucet or to hose thread

  1. To the faucet, connect the backflow device (model D45), then a 25 PSI pressure regulator (model D46) and then a 3/4″ swivel adapter with screen (model C34). If water quality is a concern, we highly recommend using DIG’s fine mesh 3/4″ filter with 155-mesh (model D57A)
  2. To automate the system, install one of DIG’s hose end timers before (upstream of) the backflow device.
  3. The 3/4″ FHT backflow preventer should only be used to keep contaminated water from re-entering the household/municipal water supply lines and in areas where discharge or spilling of water will not cause damage.