Break pressure tank: need and construction

Why a break pressure tank is needed

In a gravity scheme laid on steep ground, the static pressure at the lower part of the pipe becomes very large (it increases by 1 kg/cm² for every 10 m drop). This can burst pipes, joints and taps, and needs expensive high-class pipes. A break pressure tank (BPT) is a small open tank placed along the pipeline that makes the water pressure zero (atmospheric) at that point, so the static head of the next section is reduced to the height below the tank. Thus lower-class pipes can be used, and pressure at taps stays within safe limits (generally below 60–70 m).

It is also used to remove air and reduce the energy of the incoming water.

Construction

   inlet pipe (from above)
        |      float valve
     ___|_____ /___ vent/cover
    |   ~~~~~~~~~   |-- overflow
    |   water       |
    |_______________|-- outlet to next section
        washout

• The tank is built of stone/brick masonry or RCC with cement plaster, usually 1 m × 1 m to 1.5 m × 1.5 m in plan and about 1–1.5 m deep (volume is just enough to hold a few minutes' flow).
• Inlet pipe with a ball (float) valve closes the supply when the tank is full.
• Outlet pipe to the next section, at 100–150 mm above the floor, with a strainer.
• Overflow pipe, washout pipe for cleaning, a vent, and an RCC cover with a manhole for inspection.
• Free board about 0.3 m. A fence is provided around it and the site is drained.