Boiler is one of the most important machinery on the ship. An economic and efficient working of a marine boiler on a ship requires timely maintenance and special care in starting and stopping the boiler. Routine cleanup is extremely helpful in increasing the working life of a marine boiler.
In this article we have brought to you one such important procedure – boiler blow down, which has to be performed at regular interval of times in order to increase the performance of the boiler.
Boiler blow down
Boiler blow down is done to remove carbon deposits and other impurities from the boiler.
Blow down of the boiler is done to remove two types of impurities – scum and bottom deposits. This means that blow down is done either for scum or for bottom blow down. Moreover, the reasons for boiler blow down are:
1. To remove the precipitates formed as a result of chemical addition to the boiler water.
2. To remove solid particles, dirt, foam or oil molecules from the boiler water. This is mainly done by scum valve and the procedure is known as “scumming.”
3. To reduce the density of water by reducing the water level.
4. To remove excess water in case of emergency.
Procedure for Scumming and Bottom Blow Down
Below is the procedure for boiler blow down using the blow down valve located at the bottom of the boiler. In order to do scumming, instead of bottom blow down, the scum valve is to be opened.
Steps for blow down procedure are as follows:
Kindly refer the diagram to understand the blow down procedure properly.
1. Open the overboard or ship side valve(1) first.
2. Open the blow down valve (2), this valve is a non-return valve.
3. The blow down valve adjacent to the boiler (2) should be opened fully so as to prevent cutting of the valve seat.
4. The rate of blow down is controlled by the valve (3).
5. After blow down close the valve in reverse order.
6. A hot drain pipe even when all valves are closed indicates a leaking blow down valve.
You may also like to read: Procedure for Boiler gauge glass maintenance.
Image Credits: Book of operation and maintenance of machinery in motorship by N.E Chell