Blowdown Valves

Materials Used

Features

Types

Uses

The blowdown valves are a very popular category of pipe valves, used in a wide variety of applications. They are used for operation in open position. The main function of blowdown valve is mainly to control a continuous flow of steam /fluid under high differential pressure. The outstanding feature of this type of valve is that it can maintain fluid tightness and it is easily operated without the help of any wedging action.

Materials used:

• Brass
• Bronze
• Copper
• Aluminum
• Stainless steel
• Cast Iron
• Zirconium
• Nickel
• Monel etc.

How does a blowdown valve operates?

• At start-up, the valve closes. This leads the air-oil separator pressure to build up.
• At shut-down the valve opens to bleed the air-oil separator to atmosphere. This is when a pressure is applied. The valve can also be used as a by-pass valve to bleed air with the help of the compressor at start-up.

Features of blowdown valves:

• The design and materials of blow down valves must be such as to minimize the effects of a fluid stream in conditions where water contains sometimes abrasive particles.
• The outlet of such valves is always "Venturi tube" shaped.The stem is rising non rotating.
• There is a local stroke indicator which shows the position of the disk.
• The bonnet less design of the valve helps in easy dismantling, inspection and maintenance.

Types of blow down valves:
Some types of blowdown valves are as follows:

• Surface blowdown valve: This is supposed to be the best choice for blowdown valves. It is used for removing dissolved solids. It helps in removing solids at those points where they are most concentrated.
• Bottom blowdown valve: This is another type of valve for controlling dissolved solids. The function of this type of valve is to remove sludge which gathers in the bottom of the boiler.

Factors to influence blowdown rate:

• The size of the blowdown line.
• The boiler pressure.
• The length of the blowdown line between the blowdown vessel and the boiler.

Uses of blowdown valves:
Certain uses of these valves are as follows:

• These valves are appropriate for use with air compressors.
• They are used to help in the removal of slug and unwanted materials after cleaning the pipes.
• Blow down valves are found on the water feeders.
• They are also used to lower water cut-offs.
• They can control the concentration of solids in the boiler.