Valves Used in the Chemical Industry
Valves are critical components in the chemical industry as they perform several functions. Not only do they deliver precise control and dosing, they also monitor pressure, protect other equipment, and must be compatible with the flow media. Thus, it is imperative that valves are fit for purpose. In this article, we discuss the most common valves in the chemical industry, material compatibility with process media, and finally, how chemical injection valves work.
Common Valves in the Chemical Industry
While a plethora of valves exist in the chemical industry, this section focuses on the most common options.
Ball Valves
Ball valves consist of a ball with a hole in the center that rotates to control flow and pressure across the valve. As a quarter-turn valve, only a 90° rotation is necessary to fully open or fully close the valve, which delivers speed in actuation and makes it easy to automate the process.
Ball valves are easy to operate, maintain, and offer low resistance to flow. Another feature that makes these valves one of the most common in the chemical industry is the air-tight seal they deliver in the closed position. Even after long periods of inactivity, they remain leak-tight and effectively shut off corrosive and aggressive fluids. The tight shutoff provides an ideal deployment in applications that require a high degree of accuracy such as gas distribution.
Globe Valves
Similar to ball valves, globe valves are also effective in regulating the flow of liquids and gases. Also, they are highly reliable and can withstand high temperatures and pressures. The main advantage of using these valves is their precise regulation of flow, although they remain effective in shut-off applications too.
Because there is a minimum of two changes in the direction of flow across the valve, globe valves are associated with relatively high-pressure losses. Globe valves are effective in controlling the flow of corrosive and abrasive chemical solutions, as well as sticky slurries and suspended solids. This is why they are common in pumps and other systems where there is a need for throttling.
Butterfly Valves
Butterfly valves are lightweight and easy to install, making them ideal for large-bore applications. They have a simple design involving a disc, which rotates on an axis perpendicular to flow to either allow or obstruct it. As a result, they are quarter turn valves, ideal for throttling, and easy to automate. In addition, butterfly valves are suitable for corrosive liquids at low temperatures and pressures. However, if proper sealing is a major concern, then other valve types should be considered, especially on a long-term basis.
Gate Valves
Gate valves feature a disc that swings perpendicular to flow either to allow or obstruct it. Generally, these valves only operate in fully open or closed positions. This is because partial opening exposes internal components to wear due to flow pressure impact on the gate/disc.
Gate valves take up little space in the pipe axis and constitute no obstruction when flow passes through, ensuring minimal pressure drop across the valve. In the chemical industry, gate valves are preferably used to isolate liquid flow, although they could serve to some extent when the flow media is gas or solids.
Check Valves
Check valves are two-port, self-actuating valves that open or close in proportion to the flow velocity/pressure. The first port allows flow into the valve, and the second port exits flow from the valve. As a result, they are always customized to meet specific flow requirements.
They allow liquid or gas to flow in only one direction, thus, preventing potential damages from backflow. This one-way flow function makes check valves a popular option in chemical pumps, compressors, and storage tanks. Also, they serve as pressure relief valves in low-pressure gas applications, thus preventing contamination or damage of downstream equipment.
Diaphragm Valves
These are bi-directional, throttle valves that control fluid flow by regulating the area with which the media can enter and exit the valve. Its unique design makes them ideal for controlling the flow of hazardous and corrosive chemicals. Diaphragm valves are highly reliable and low maintenance. Their features make them popular in the chemical industry for drainage, filtration, and dosing applications.
Material Compatibility with Process Media
Compatibility lookup of valve material with process media is key to ensuring optimal performance over the operational temperature range. Typically, valve parts constitute metals and polymers, especially thermoplastics and elastomers. Metals are more durable and resilient to varying operational conditions, but increase friction on moving parts. Polymers minimize friction and offer more flexibility, but are sensitive to temperature variations.
Metals
Valve components such as the body, bonnet, stem, disc, and springs are frequently formed of metal. Various types of metal are chosen based on the process conditions.
- Carbon Steel: Operates effectively for medium and high-pressure valves between -29℃ and 425℃. This material is applicable to water, liquefied natural gas, compressed air, oil, superheated steam, etc.
- Cast Iron: Applicable to valves carrying water, gas, etc at temperatures between -15℃ and 200℃ with nominal pressure not exceeding PN16.
- 400 Series Stainless Steel: The 400SS commonly serves as valve stem material in butterfly valves, as well as backseat bushings and wedges in cast steel valves. They are resistant to high-temperature oxidation and offer better physical and mechanical properties than carbon steel.
- 300 Series Stainless Steel: This series generally provides more ductility than the 400SS and is common in valves as stem, body, and ball materials. Common grades include 304, 317, and 347. The most common variant, 316SS, offers good corrosion resistance for a wide range of environments and is not susceptible to stress corrosion cracking.
- Monel Alloy: Mainly serves in valves carrying hydrofluoric acid medium.
- Hastelloy Alloy: Suitable for diluting sulfuric acid and other strong corrosive media.
Polymers
Polymers are usually for components such as diaphragms, o-ring seals, and ball seat rings in ball valves.
- Viton: Possesses superior chloramine resistance for drinking water applications. Also has strong resistance to chemicals such as petroleum oils, silicon fluids, and acids at high temperatures up to 400℉.
- Buna-N(Nitrile, NBR, HNBR): Has resistance to petroleum products, lubricants, and water between -50 to 200℉. Buna-N is not ideal for outdoor applications where there is exposure to ozone, sunlight, or weather. Moreover, High Nitrile Buna-N is suitable for H2S and other harsh fluids.
- PEEK (Poly Ether Ether Ketone): Excellent water and chemical resistance for temperatures between 70 and 500℉. Not porous, so ideal for high-pressure and high-corrosion environments.
- EPDM/EPR (Ethylene Propylene Diene): Strong resistance to ozone, certain hydraulic fluids, brake fluids, and water between -50 and 250℉. However, it has poor resistance to petroleum-based fluids, mineral oils, and solvents.
- PTFE (Polytetrafluoroethylene): Provides reliable integrity in high-purity fluid transfer applications such as the food and beverage industry. Also effective in chemical processing in the semiconductor and pharmaceutical industries. PTFE possesses a wide operating temperature range between -50 and 400℉.
Generally, valve manufacturers have compatibility charts showing details of the performance of various materials in process media. Sometimes, there is a wide variation in performance details depending on the manufacturer. Thus, it is necessary for designers to utilize these charts as a guide during the selection process.
How Chemical Injection Valves Work
Chemical injection valves introduce other chemicals into a flow stream by pumping the chemicals at a higher pressure than the current line pressure. The pressure of the chemical line needs to be higher to avoid the occurrence of siphoning.
Generally, positive displacement pumps serve to deliver the pressure requirements. The injection valve typically consists of a series of check valves that help prevent backflow. The chemical injection process increases production, reduces corrosion, and separates mixtures to improve the efficiency of a setup.
Knowing that you require a valve is the first step, and the second step? Knowing what valve you need. The tricky part, there are a variety of valves available, all with different abilities for a wide range of applications. Selecting the correct one for your needs can be made simple if you know exactly what each valve's job is.
We have created this guide that provides you with information regarding the 13 different valves you can find in the industry. We have included what they are, common uses and the sizes, and materials they are available in.
Ball Valves
Ball valves are designed with a spherical disc, which is the part of the ball valve that controls the flow through it. There is a hole in the middle of the sphere so that when the hole is in line with both ends of the ball valve, the flow will occur. When the handle, which is a 90° turn, is moved to the close position, the hole is perpendicular to the ends of the valve, blocking the flow.
Ball valves are commonly used in locations where a shut off valve is needed. They are also available with different end connections and in multiple materials including stainless steel, brass and plastic. The different end connections available are threaded, C x C, push fit, compression, barbed and PEX.
For a closer look at ball valves, check out our blog: What the Heck is a Ball Valve?
Gate Valves
Gate valves, also known as slide valves, have a linear motion that incorporate a flat closure called a gate. Gate valves can either include a hand wheel, that requires multiple cranks, that you can turn (counterclockwise) to open or (clockwise) to close, or you will need to push or pull the gate to operate the gate valve. Both designs minimize the drop in pressure across the valve. When fully opened, the diameter of the opening is the same diameter as the pipe as to which the fluid is flowing and no direction of flow is being altered.
Common applications for gate valves are systems that handle viscous liquids like heavy oil or light grease. They are available in sizes up to 4". For more information on gate valves, check out our blog: When you Should Use a Gate Valve.
Relief Valves
Relief valves are a safety device that prevent pressure from exceeding the maximum allowable working pressure. The relief valve minimizes the risk of any catastrophic failures and it protects other components of the system. Relief valves are spring loaded which mean they open in response to the system pressure.
Relief valves are typically used in potable water applications and are specifically designed for installation on cold water service lines. They are available in a variety of materials including brass, stainless steel and PVC. To take a closer look at relief valves, we have a blog you can check out: 3 Reasons to Install a Relief Valve.
Plug Valves
Plug valves are an energy efficient, round port, eccentric, quarter turn plug that is designed with a fusion bonded epoxy coated ductile iron body. Plug valves are used in a variety of applications including situations where slurries, solids or grit are present like wastewater and sewage lines and in wastewater treatment plants.
Flo-E-Centric® Plug Valve with Bare Stem, Model 54-B | Flomatic
Sump Pump Check Valves
Check valves allow media to flow through the valve, only in one direction. When the pump is running, the water flows through the valve, when the pump shuts off, the water naturally wants to flow backward toward the pump. A check valve prevents the water from heading back toward the pump by allowing the weight of the water to push down the flapper, causing it to close.
Sump pump check valves are used to pump the ground water out of your home before it would enter your basement. The water is collected in the sump tank and then the sump pump ejects it to a safe distance away from your house.
There are two operating designs: spring loaded, and rubber flapper. Sump pump check valves are available in ABS. We wrote a blog taking a closer look at sump pump check valves. Read it here.
Spring Check Valves
Spring check valves, available in brass, bronze & stainless, have a poppet that hold the spring in place. When pressure is put on the inlet side of the valve, it forces the poppet to open and the spring to contract. When the pressure subsides, the spring forces the poppet closed. These types of check valves can be installed both vertically and horizontally.
Spring check valves include NPT (National Pipe Thread) connections on both ends and they are installed directly into the piping system. The main reason to include a check valve in your system is to extend the efficiency and life of your pump.
For further information on check and foot valves, check out our blog: Taking a Look at Check & Foot Valves.
Foot Valves
Foot valves usually have an NPT connection on the outlet side, and on the inlet side, they have a strainer. The strainer is there to prevent any large debris from clogging up the foot valve when it's open, which would cause damage to the water pump if not prevented. Typically, foot valves are used in shallow well jet pump and deep well jet pump installations.
Similar to a check valve, foot valves prevent water from flowing back out of the jet pump. Foot valves are available in materials such as brass, bronze, PVC, stainless steel and cast iron.
Butterfly Valves
Butterfly valves have a rubber seated design that is providing bi-directional bubble tightness. Butterfly valves are best suited for throttling services and operation after long periods of stagnation. They are availble in a variety of configurations including, gear operated, handle operated and electrical actuated.
Azure® Gear Operated Flanged Butterfly Valve | Flomatic
Air Release Valves
Air release valves are used to vent air that accumulates while the system is under pressure. Including an air release valve, will improve flow and pump efficiency. It is recommended that air release valves are installed on high points of the pipeline and approximately every MINIAIR® Air Release Valve for Clean Water Applications | Flomatic 2000 feet of horizontal segments of the pipe. They are available in sizes 3/8"- 4".
Sediment Faucets
Sediment faucets are valves that are commonly used to provide a way to flush the sediment that builds up in the unit. It also provides a means to drain the vessel if the system needs service or for winterization in some situations.
These brass valves are available in two different designs: one design, the valve stem and hand wheel are in-line with the inlet connection and the only part angled is the hose bibb outlet. In the other design, the valve body is molded with an angle.
Stop & Waste Valves
Stop & waste valves are mainly used in residential applications where a 1/2" or 3/4" shut off valve is needed. The valve contains a brass body with either a female thread, solder, PEX or compression connection and a hand wheel that allows you to shut it off.
It is recommended that you include a valve that you can shut off for every appliance in your home incase something needs replaced or repaired. This way you don't have to shut off the water for the entire house.
Constant Pressure Pump Control Valves
Constant pressure pump control valves are commonly found in irrigation applications like golf courses and schools but can also be used in water well pumps for domestic or municipal water. They automatically regulate downstream Direct Acting Constant Pressure Control Valve - Cycle Gard® I C152E | Flomatic pressure while providing constant pressure (regardless of the system water flow) demand until it is no longer required.
Float Valves
Float valves are used to control the level of fluid inside the tank. A float valve has the ability to control the level by opening and closing the valve when the levels change. A basic float valve includes an air-filled float that is attached to an arm that is sealed to make sure water cannot get in.
Typically, float valves are found in applications in the Agriculture and Industrial industries. But they can also be found in places like aquariums and even the back of your toilet. They are available in brass and PVC and in a variety of sizes.
To learn more about these types of valves, check out our blog: Taking a Closer Look at Float Valves.
In Conclusion:
There are a wide range of valves available, and we hope this guide helps you determine what each valve's best suited application is.
The biggest thing all the valves have in common is the ability to stop & control water flowing in a system. It's just up to you to determine which one fits your system the best.
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