Blowdown Valves

What is a Blowdown Valve & what is its function?

Blowdown Valves keep boilers clean. Blowdown valves are used to vent the impurities, sediment, and other solids that are present in boiler water. They are opened periodically to prevent buildup. They are also used to regulate the conductivity of the water in a boiler, because higher electrical conductivity causes scale to build up faster.

Different Types of Blowdown Valve & How to Choose

Blowdown valves come in two varieties, fast-open and slow-open. Fast-open valves act as the quick cutoff, while slow-open valves allow modulation of the water flow.

During a blowdown, the fast-open valve is opened first. This feeds the slow-open valve, which can then be opened gradually for operator safety and to prevent thermal shock to the drain pipes. 

The Role Blowdown Valve Play in a Boiler

There are four locations where blowdown valves are typically installed: 

• The bottom of the sight glass to keep water readings accurate
• The bottom of the boiler to remove heavier solids, sediment, and impurities
• Level with the surface of the water inside the boiler to allow floating impurities to be blown out
• The low water cutoff, to confirm that it is operating properly

How blowdown valves make a difference

Without the blowdown valve in place, sediment and other impurities would gradually build up along the inside surface of the boiler. This would not only reduce the boiler’s operating efficiency, it could also become a safety hazard by creating uneven heating and metal stress.

Blowdown valves also regulate electrical conductivity in the boiler water by regulating the amount of suspended solids. Higher electrical conductivity creates faster scale buildup, which reduces a boiler’s operating efficiency. Higher conductivity also decreases the life of the boiler by accelerating the corrosive effects of the oxygen inside. 

what are the Effects of a Bad Blowdown Valve?

A blocked blowdown valve won’t vent boiler water properly. If you’re not getting a good, solid flow, it’s time to have your blowdown valve checked.

Things to Consider about Blowdown Valves:

• When the blowdown valve is opened, the water is extremely hot, and has a lot of steam pressure behind it. Always use extreme caution and be aware of your environment when operating a blowdown valve. 
• Always wear proper protective equipment when operating a blowdown valve.
• Open the valve slowly. This is not only for operator safety, it also reduces thermal shock to the venting pipes.
• After completing a blowdown, momentarily crack the slow-open valve to release the pressure between the valves. 

Helpful Resources

Relevant WARE Videos on Blowdown Valves

Boiler Blowdown Valves

Using a Blowdown Separator in the Boiler Room

Inside of a Blowdown Separator and Differences between a DA and Condensate System

Explaining The Blowdown Separator

Importance of a Blowdown Line for Sight Glass

How to do Surface Blowdown on the Boiler

Everlasting Valves and Boiler Blowdown

Differences Between Slow and Quick Blowdown Valves

Determining If you have a Leaking Bottom Blowdown Valve

Difference between Deaerator and a Condensate Tank

Revisiting Daily Boiler Maintenance

Daily Steam Boiler Maintenance in the Boiler Room

Explore over 750+ explanatory videos on boilers and boiler systems on our Youtube channel. Our videos can help you quickly grasp complex boiler topics. Watch more here!

Relevant WARE Blog Articles on Blowdown Valves

Monitoring Your Boiler Room

Explaining The Blowdown Separator

How to Do a Boiler Blowdown

Boiler Blowdown – How Doing the Simple Things Can Optimize Your Boiler Operation

Planning a Rental Boiler Contingency

Daily Steam Boiler Maintenance in the Boiler Room

Level With Me

Our informative and educational blog content can help you gain a deeper understanding of the boiler room. Read more here!

Technical Documents

Rental Contingency Plan

Blowdown Valves FAQ

How do I know when to blow down my sight glass?

If your sight glass water is cloudy, or if you notice any solids settling inside, it’s time for a blow down. 

How long do I blow down my boiler?

For high conductivity, a blowdown should last no more than fifteen seconds to avoid running the boiler water down.

For a low-conductivity blowout, just a few seconds usually does it. 

How do I check my conductivity?

There are two ways to check a boiler’s conductivity:Measuring the total dissolved solids – the higher the total dissolved solids, the higher the conductivityUsing a conductivity sensor – measures conductivity electronically