Intermittant Blowdown - Continued.

Under normal operation, the water exiting the mud drum consists of a lot of solids and has erosive properties. The boiler water erodes the IBD valves as it rushes through. Eventually, the valves are not able to provide proper sealing. To protect against such problems, the following procedure is followed:

a. To start the IBD, fully open valve B. At this time, no water flows through the pipe since valve A is still closed. Therefore, valve B does not experience any rush-through of water.

b. Now, open the valve A quickly for a few seconds (according to authorized procedures). As this valve is opened it does experience high-velocity rush-through of water.

c. Close valve A after the requisite time. It again experiences high velocity due to the throttling action.

d. Close valve B. Again this valve sees no flow-through of high velocity water.

This procedure limits the wear and tear to valve A, while valve B is protected and provides excellent sealing and isolation.