Boiler Blowdown

Blowdown of steam boilers is very often a highly neglected or abused aspect of routine boiler room maintenance. The purpose of boiler blowdown is to control solids in the boiler water. Blowdown protects boiler surfaces from severe scaling or corrosion problems that can result otherwise.


boiler blowdown

There are two types of boiler blowdowns - continuous and manual. A continuous blowdown utilizes a calibrated valve and a blowdown tap near the boiler water surface. As the name implies, it continuously takes water from the top of the boiler at a predetermined rate

 A continuous blowdown is an optional feature and may not be included on your steam boiler. However, all steam boilers should include a means for manual blowdown as standard equipment.

Manual blowdowns are accomplished through tapings at the bottom of the boiler. These openings allow for the removal of solids that settle at the bottom of the boiler. Manual blowdown is also used to keep water level control devices and cutoffs clean of any solids that would interfere with their operation. All steam boilers require manual blowdown whether or not they are supplied with continuous blowdowns.


Proper blowdown is performed as follows:

Blowdown should be done with the boiler under a light load. Open the blowdown valve nearest the boiler first. This should be a quick opening valve. Crack open the downstream valve until the line is warm. Then open the valve at a steady rate to drop the water level in the sight glass inch. Then close it quickly being sure that the hand wheel is backed off slightly from full close to relieve strain on the valve packing. Close the valve nearest the boiler.

Repeat the above steps if the boiler has a second blowdown tapping. Water columns should be blown down at least once a shift to keep the bowls clean. Care should be taken to prevent low water shutdown if this will affect process load. 

Please keep in mind that all blowdown piping should be checked once a year for obstructions.



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P.C. McKenzie Company
P.O. Box 112638
Pittsburgh, PA 15241
Fax: 412-257-8890
Phone: 412-257-8866
P.C. McKenzie Company
1365 McLaughlin Run Road
Pittsburgh, PA 15241

Boiler Blowdown