Continuous Blowdown Valves

Keep Boiler Water Clean with Minimal Water Loss

The continuous blowdown valve (CBD) is designed to continuously remove water from the boiler.  It does this by continuously removing water from the surface of the boiler water. The CBD is also known as a surface blowdown valve. 

Blowdown valves are used either continuously or intermittently depending on the service requirement. An intermittent blowdown (IBD) valve, located close to the bottom of a boiler, is also called a bottom blowdown valve and removes sediment from a boiler. Both CBD and IBD valves play an important role in fossil fuel boilers to remove dissolved solids from the water. 

How Continuous Blowdown Valves Work

A CBD valve works by creating a continuous draining from the surface layer of the furnace water where it is most concentrated. The purpose is to reduce the salinity and alkalinity of the boiler water, preventing the concentration from being too high. High concentration affects the quality of steam from the boiler. A CBD valve is generally installed at normal water level. Boiler water continuously evaporates and concentrates, which causes the highest concentration of salt to be near the water surface. The continuous drainage orifice should therefore be installed near the surface, where it can continuously discharge high-density boiler water and replace it with clean feed water. 

As a result, proper boiler water quality can be maintained at all times. Also, a maximum of dissolved solids may be removed with minimal loss of water and heat from the boiler. The drainage rate is usually only 1% of the evaporation volume.

Another major benefit of continuous blowdown is the recovery of a large amount of its heat content through the use of blowdown flash tanks and heat exchangers. We recommend that control valve settings be adjusted regularly to increase or decrease the blowdown according to control test results. This will allow you to maintain the level of boiler water concentrations at all times.

United Brassworks offers two models of CBD valves, an angle pattern and globe pattern. Both have easy-to-read calibrated gauges with pointers.