Stainless Steel Butterfly Valve

What is stainless steel butterfly valve? 

A stainless steel butterfly valve is a valve that is made of stainless steel material. Although this valve is made of steel, other internal components like seats, seals, O-rings, and gaskets can be made of different materials like plastic, rubber or other material. The type of material used to make those internal components determines the type of media and temperature the valve can be used on. SS butterfly valves made of fully metallic materials are suitable for use in both low and high temperatures because metallic materials can withstand high levels of thermal heat. Stainless steel butterfly valve manufacturers design these valves for heavy-duty and harsh conditions. As such, these valves are very strong and they can withstand high pressure and slurries flawlessly. SS butterfly valves operate manually or automatically. These valves’ operation depends on the hand wheel’s quarter turn to start or stop fluid flow. The quarter turn of the handwheel makes these valves fast operating and less tedious relative to other valves that need multiple turns to operate. 

Figure: Stainless steel butterfly valve.

Components of a stainless steel butterfly valve 

Handwheel/actuator 

This is the component that provides the power to start and stop the valve. The handwheel is used in manual valves and it is where the operator applies force to open and close the valve. The actuator is used in automatic valves and provides the automation and force needed to open and close the valve. 

Body 

This is the main part of the SS butterfly valve which is meant to house internal components. The body is usually made of stainless steel material. Since stainless steel material is very strong, it transfers its strength to the SS butterfly valve resulting in a valve that can withstand high-pressure, high temperature, and high impact damage. The body contains the valve inlet and outlet ports. 

Stem 

This is a shaft that connects the valve actuator or handwheel to the valve disc. The function of the stem is to transmit power from the handwheel/actuator to the disc to help in starting and stopping fluid flow. 

Disc 

This is the main component of the SS butterfly valve as it is the one that performs the opening and closure of the fluid flow. Disc gets its rotary force to start and stop the valve from the handwheel/actuator through the stem. 

Seats 

Stainless steel butterfly valve manufacturers design this valve with two seats. The seat helps to prevent leakage when the valve is closed. The seat is where the disc rests when the valve stops. 

Packing

This is a material used to prevent fluid leakage between the valve and the stem. It also prevents dirt and dust from entering the valve.

Gaskets 

This component prevents fluid leakage between the pipe and the valve connection. The gasket is placed between the valve and pipe and it is held in its position by use of bolts and nuts. 

Figure: Components of a stainless steel butterfly valve.

How does a stainless steel butterfly valve work? 

A SS butterfly valve operates when rotary force is transmitted to the valve disc. The disc is responsible for opening and closing fluid flow. This valve is usually operated via a handwheel/hand lever or actuator. The working principle of both the manual and the actuated valve is the same. To start a stainless steel butterfly valve, the handwheel is rotated in the counterclockwise direction. This rotary force applied on the handwheel or hand lever is transmitted to the disc via the stem. This then forces the disc to make a 90^o degree turn in the counterclockwise direction where it aligns itself parallel to the fluid flow. This creates a free passage for the fluid to flow through the valve. To stop the SS butterfly valve, the handle is rotated clockwise where it returns the valve disc to the seating position. In this position, the disc turns to be normal to the fluid flow ensuring no fluid can cross through the valve. Stainless steel butterfly valve manufacturers make these valves for use in throttling fluid flow. For throttling, the handle is rotated slightly according to the amount of fluid the operator wants. 

Figure: working of a SS butterfly valve.

Types of Stainless steel butterfly valves 

Stainless steel wafer butterfly valve

This is an SS butterfly valve that is connected to the piping system by placing it between two pipe ends which are connected by long bolts crossing the valve body. Stainless steel butterfly valve manufacturers produce this valve with or without flange holes on the valve body. Gaskets and O-rings are mounted on both the inlet and outlet flat sides of the valve and the pipe flanges to create a bubble-tight seal. This connection is the most economical compared to others used in other butterfly valves. However, with this design, these SS butterfly valves cannot be used in end-of-line service or as isolation valves. Another challenge associated with these valves is that the piping system has to be shut down on either side when the valve is being repaired. 

Figure: Stainless steel wafer butterfly valve.

Stainless steel lug butterfly valve 

This is a SS butterfly valve designed with threaded lugs on the outside of the valve body. The valve is mounted into the piping system by placing it between two pipe flanges. Bolts are used to tighten the connection between the valve and the pipe. Two separate sets of bolts are used to support the valve on each side without the use of nuts. As such, this valve can be used in end-of-line service or as an isolation valve. Stainless steel butterfly valve manufacturers recommend this design where less amount of time is needed when doing repair and maintenance as the valve can be dismantled on one end without affecting the other end. This design has the challenge of weight since the pipeline weight is distributed on the valve body. As such, the valve needs to be strong to withstand such loads. 

Figure: Stainless steel lug butterfly valve.

Stainless steel double-flanged butterfly valve 

This is an SS butterfly valve that has two flanged ends one on the inlet and another one on the outlet side. The flanged ends are of equal size and have holes of the same size. This valve is connected to the pipe using bolts and nuts. The pipe ends to be connected to the valve are designed with flanges and holes of the same size as those on the valve. Stainless steel butterfly valve manufacturers produce these valves for use in high-pressure applications and other harsh conditions where other small-sized valves would be uneconomical to use. These valves are heavier compared to other stainless steel butterfly valves due to the use of many bolts and nuts and flanged ends. 

Figure: Stainless steel double flanged butterfly valve.

Butt-weld stainless steel butterfly valves 

This is an SS butterfly valve that is connected to the pipe by welding. Stainless steel butterfly valve manufacturers recommend the use of these valves where the valve will not be used frequently to make it economical. This is because the valve cannot be opened for repair or cleaning while it is in the field. For repairs, the weld has to be removed first. These valves are leakage-proof due to use of the weld connection unlike a gasket which may wear out and cause leakage. This SS butterfly valve is suitable for use in highly hazardous and flammable fluids which, in case of any leakage, may cause a lot of environmental damage or injuries to the valve operator. 

Figure: Butt-weld stainless steel butterfly valve.

Concentric stainless steel butterfly valve

This valve is also known as stainless steel zero offset butterfly valve. This is the most basic design of a SS butterfly valve. As the name suggests, the stem passes through the disc center-line. This results in the stem centerline being collinear to the pipe bore. The seat is placed in the periphery of the valve body diameter. Stainless steel butterfly valve manufacturers produce these valves with rubber seats. These concentric buttefly valves are used in low-temperature and low-pressure applications due to the soft seats. One advantage of this valve is that the fluid flowing will not reach the body because the seat is made as a cartridge or sleeve in the valve body.

Figure: Concentric stainless steel butterfly valve.

Applications of Stainless steel butterfly valves 

• Heating ventilation and air-conditioning (HVAC) systems. 
• Wastewater treatment applications. 
• Mining industries. 
• Steam power plants to control water and steam flow. 
• They are used in the manufacturing of various chemicals. 
• Processing of foods and beverages. 
• Refinery of petroleum products. 
• Manufacturing of sugar. 
• Oil and gas transportation. 

Advantages of stainless steel butterfly valves 

• These valves are very strong and durable making them economical. 
• They are fast operating relative to other valves. 
• These valves occupy small installation space relative to other valves like globe valve, ball valve and gate valve. 
• Allow bi-directional fluid flow.
• They can be used in high and low temperatures. 
• Resistant to corrosion and abrasion.  
• Easy to repair, clean, and install. 
• Shut-off and throttling flow applications. 
• These valves are small in size and light in weight. 
• They are of simple and compact in design. 

Disadvantages of stainless steel butterfly valves 

• Stainless steel material is expensive and this increases the cost of the valve. 
• These valves open when the disc is at the center of the fluid flow and this reduces pressure and thus lowers efficiency. 
• Use of SS butterfly valves in throttling flow is recommended if the pressure drop is low. 

Troubleshooting stainless steel butterfly valve

Leakage between the actuator/handwheel and the valve

• Worn out packing. Replace the packing. 

Leakage through the bottom trunnion

• Worn out gasket, O-rings, or packing. Replace the gasket, O-rings, or packing as necessary. 

Leakage when the valve is closed 

• The disc is loosely closed. Turn the handwheel to tighten the disc. 
• Worn out disc. Repair or replace the disc as necessary. 
• Damaged seat. Replace the seat. 
• Dirt in the valve. Open the valve and clean the dirt. 

Leakage through pipe-valve connection 

• Worn out gasket or O-rings. Replace gasket or O-rings as necessary. 
• Loose bolts. Tighten the bolts to attain the torque recommended by the stainless steel butterfly valve manufacturer. 
• Too high fluid pressure. Ensure the fluid pressure matches the range given by the stainless steel butterfly valve manufacturer.

Valve is hard to operate 

• Foreign materials in the valve. Open the valve and remove any foreign materials. Clean the valve interior. 
• Corrosion inside the valve. Open the valve and clean the corroded components. 

Summary 

Stainless steel butterfly valves are made of stainless steel material. The reason for manufacturing these valves using stainless steel is to ensure the valve is strong. The high strength is important as it helps the valve work flawlessly in high pressure and high temperatures.

Stainless steel butterfly valve manufacturers do not produce these valves fully using stainless steel material but also combine them with other materials. Such materials are used to make internal components like seats, O-rings, gaskets, and packing. The material used to make such internal components determines the type of media and temperature the valve can work on.