What is a Drain Valve or Scour Valve?

Valves are necessary in water supply system, in order to regulate the flow of water and to minimize the wastage of water. Valves either start/stop the flow of water or control (throttling) the speed and capacity of water or direct the flow in one direction only.

Drain Valve is also called as Blow –off Valve and Scour Valve. These are ordinary valves but used for a specific purpose of scouring or emptying or cleaning the main and water storage tank. The drain valve is provided at the lowest point of the section of the pipeline to be drained and at all dead ends of the distribution system. The size of drain valve is generally half the size of the main pipeline. The drain valves generally discharge into natural course.

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The exact location of drain valves is frequently influenced by opportunities to dispose off the water. Where the main pipeline crosses a stream or drainage structures, there will usually be a low point in the line but if the main pipeline goes under the stream or drain, it cannot be completely drained into the channel. In such a situation it is better to locate a scour connection at the lowest point that will drain by gravity and provide for pumping out the part below the drain pipeline.

There should be no direct connection to sewers or polluted watercourses. By providing specially designed trap or pit, we can provide the direct connection to sewer or polluted watercourses. For more safety, two blow-off valves are placed in series. The outlet into a channel should be above the high water level and if the outlet must be below high water, a check valve or Non-return valve must be placed to prevent back flow.
In a house, drain valve have two applications:

  1. At bottom of water storage tank – A drain valve is provided at the bottom of the water storage tank to empty the tank for cleaning purpose.
  2. At bottom of water storage heater – A drain valve is provided at the bottom of water storage heater to empty hot water from the water heater.

The size of the drain valve depends on time in which a given section of pipeline is designed to be emptied and also depend upon the resulting velocity of flow. Its frequency of operation depends upon the quality of the water carried, especially on silt loads.

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