Knife gate and slurry valves
Usage & Applications
Knife gate and slurry valves are rarely used where conventional valve designs such as gate, globe, ball, plug or butterfl y valves would work well. In particular, these designs are seldom used in services involving clean liquids or gases as their limitations far outweigh the advantages. However, where solids (free fl owing powders), mixtures of liquids and solids, or solids and gases are involved, these valves provide superior functional features and service life compared to conventional valve designs. Knife gate and slurry valves are predominantly used for shut-off/isolation services as “On/Off” valves. They are seldom used to throttle fl ow or as control valves as the media they handle are not suitable for throttling. However, few exceptions and some special designs do exist for these limited throttling applications. Major industrial sectors where these valves are applied are shown in Fig-5.
Media handled
Typical types of media where these valves are used.
Liquid + solid
These mixtures occur in a variety of industries and form the primary area of use for knife gate and slurry valves. The mixtures vary widely in composition and are usually referred to as sludge or slurry. Typically, sludge contains relatively soft solid components whereas slurry has harder and more abrasive solid components. The composition of the solid component may vary from very small percentages to as high as 70 percent. The solid component may be present in the form of very fi ne powder or as a mixture of fi ne powder and coarse lumps. Most of these media remain homogeneous only when kept agitated and mixed well; when kept still (as in stagnant pipes or vessels) they tend to settle and form separate solid and liquid layers. Many of them dewater and harden or cement if the liquid component drains off in the service. All these factors create challenges to the effective functioning of these valves.
Solid (Powders)
Primary use with powders are to extract materials from storage vessels like silos. This application is used across a wide variety of industries.
Solid (Powders) + Gas
Primarily these applications involve pneumatic conveying systems where powders are transported; these also occur across many industries.
Gas
Some of the knife gate valve designs can handle high temperatures as well as thermal cycling better than other valve designs. Exhaust gas heat regeneration and carbon black processing are typical sectors with such services. Examples of typical media that knife gate and slurry valves handle are:
• Paper pulp
• Raw sewage
• Raw water
• Ore slurry
• Molasses
• Coal-air mixture
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Fig 5 – Main markets for knife gate & slurry valves
Knife gate and slurry valves are rarely used where conventional valve designs such as gate, globe, ball, plug or butterfl y valves would work well. In particular, these designs are seldom used in services involving clean liquids or gases as their limitations far outweigh the advantages. However, where solids (free fl owing powders), mixtures of liquids and solids, or solids and gases are involved, these valves provide superior functional features and service life compared to conventional valve designs. Knife gate and slurry valves are predominantly used for shut-off/isolation services as “On/Off” valves. They are seldom used to throttle fl ow or as control valves as the media they handle are not suitable for throttling. However, few exceptions and some special designs do exist for these limited throttling applications. Major industrial sectors where these valves are applied are shown in Fig-5.
Media handled
Typical types of media where these valves are used.
Liquid + solid
These mixtures occur in a variety of industries and form the primary area of use for knife gate and slurry valves. The mixtures vary widely in composition and are usually referred to as sludge or slurry. Typically, sludge contains relatively soft solid components whereas slurry has harder and more abrasive solid components. The composition of the solid component may vary from very small percentages to as high as 70 percent. The solid component may be present in the form of very fi ne powder or as a mixture of fi ne powder and coarse lumps. Most of these media remain homogeneous only when kept agitated and mixed well; when kept still (as in stagnant pipes or vessels) they tend to settle and form separate solid and liquid layers. Many of them dewater and harden or cement if the liquid component drains off in the service. All these factors create challenges to the effective functioning of these valves.
Solid (Powders)
Primary use with powders are to extract materials from storage vessels like silos. This application is used across a wide variety of industries.
Solid (Powders) + Gas
Primarily these applications involve pneumatic conveying systems where powders are transported; these also occur across many industries.
Gas
Some of the knife gate valve designs can handle high temperatures as well as thermal cycling better than other valve designs. Exhaust gas heat regeneration and carbon black processing are typical sectors with such services. Examples of typical media that knife gate and slurry valves handle are:
• Paper pulp
• Raw sewage
• Raw water
• Ore slurry
• Molasses
• Coal-air mixture
Fig 5 – Main markets for knife gate & slurry valves
