Procedure for Boiler Blow Down or Scum Blow Down (Scumming)

                   Boiler blow down is carried out to remove contaminated boiler water, carbon deposits or any impurities in the boiler water. Blow down can be done in two ways; scum blow down or bottom blow down. 
Main Reasons for the boiler blow down is given below,
> Deposits due to chemical addition for the boiler water purification
> To remove solid deposits at the top and bottom
> While repairing water tubes
> To reduce the water level in case of emergency

Step by Step Procedure for boiler blow down
1. Open valve No.1 ie, overboard valve or ship side valve
2. Open the valve No.3 situated near the boiler which is a non return valve. open it fully to avoid cutting of valve seat.
3. The rate of blow down is controlled by valve No.2
4. After blow down close the valve in reverse order.
5. After blow down, close the valves in reverse order

If you want  Scumming, as In step 2 Open valve No.4 instead of valve No.3


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  1. In boiler there are 3 valves as told in the post but the 2nd valve is near to boiler only. And while blowdown the valve is not opened continuously but open close open close in a very fast manner so that the sludge and mud form gets removed due to sudden opening. Of the valve is opened continuously then the mud and sludge will mix with the water and the reason for which blowdown is carried out vl be not effective .

    1. The Position of No.2 valve may be either near the boiler or near the overboard valve. i have seen both the systems.. valve No.1 and 3 should open fully to avoid the cutting of valve seat.. you can regulate the flow using no.2 valve as you said

  2. Before blowing down, we need to top up the feed water into the boiler.

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