Pressure relief valves are crucial safety devices in pumping systems, preventing catastrophic failures by maintaining safe pressure levels. These valves automatically open at a set pressure point to release excess pressure until it returns to a safe level. Various industries use them to avoid disasters, especially in high-pressure systems like chemical processing, oil and gas, pharmaceuticals, and water treatment. Failing to control pressure can lead to environmental damage, equipment issues, and harm to workers. Check valves also play a role in ensuring pump system safety. Let's explore the differences between check valves and pressure relief valves in different pumping systems.
Valves for Relieving Pressure in Pumping Systems
Often overlooked yet vitally important to many industries, valves for relieving pressure within pumping systems protect equipment and augment worker safety. These humble devices have many designs, some spring-loaded while others feature pilot-operated designs. Regardless of the mechanism, these valves open to release excess pressure whenever pressure exceeds a predetermined point within the system.
Their versatility makes them essential for many industries. Oil refineries use valves for pipelines and storage tanks to protect equipment from overpressurization, which can lead to environmental catastrophes or equipment failure if not mitigated. Valves for relieving pressure are also used in HVAC systems for large facilities. Pharmaceutical pumping systems use them to precisely control pressure, safeguard key processes, maintain regulatory compliance, and guarantee quality.
Whatever their purpose, valves for relieving pressure are integral to modern industry. But what type of valve is best for a specific application, and how does a pressure relief valve differ from a check valve?
How They Differ: Check Valve vs. Pressure Relief Valve
When deciding between a check valve and a pressure relief valve for a specific purpose, it's important to grasp their basics, similarities, and differences. Check valves are more common in low-pressure applications involving gases, focusing on ensuring material moves in the right direction. The valve opens at a set pressure differential (cracking pressure) to release excess pressure. Unlike check valves, pressure relief valves are tailored to prevent overpressure in systems, which is crucial for safety in various applications like air compressors and steam boilers.
Types of Check Valves & Pressure Relief Valves
Before discussing check valves vs. pressure relief valves in more detail, let’s briefly review some of the various types of valves.
Types of check valves include:
- Ball: These check valves have a ball that blocks flow by moving up and down. The valve is engineered to guide the ball into a conically shaped chamber toward the seat; the ball’s weight varies according to the pump’s capacity. The ball seals the flow by moving back to the valve’s seat and lifting away once pressure produces sufficient flow.
- Butterfly: Also known as a double disk, dual, folding disk, or splits check valve, both parts of the valve’s disk open toward the center as the fluid flows, sealing the pipe when the flow reverses; known for their quiet operation, butterfly check valves are often used for HVAC systems.
- Diaphragm: These check valves feature a rubber diaphragm. Their sealing surface is on the inlet side with a central opening. Positioned in the center of the seating area, backflow causes the diaphragm to cover the sealing opening, which in turn closes the inlet’s opening.
- Duckbill: Shaped like a duckbill, these check valves are fabricated from rubber or a synthetic elastomer. The valve’s open end extends to the supply line above the outlet while the opposite end remains relaxed. As pressure from upstream flows grows, the lips of the duckbill open wider to enable more fluid to flow, while conversely, when pressure decreases, the duckbill flattens and closes.
- Foot: Positioned within the lower part of the piping and connected to the pump, foot check valves feature a screen that blocks debris, with the valve’s opening larger than the line’s opening. These valves keep the pump primed so that when it’s in operation, water is pulled up via suction through the piping and valve, with fluid dropping when the pump’s no longer running.
- Globe: Effective for both gases and liquids, these can withstand high-pressure and temperature environments like those found in chemical processing facilities; they can be used as both check and pressure relief valves, though they’re mainly used to regulate flow within pumping systems that transport abrasive and corrosive solutions containing suspended solids and viscous fluids.
- Lift: Entering below this check valve’s seat, the pressure from the flow raises the ball or disk from the seat, with flow causing the ball or disk to move back to the seat once it reverses, slows, stops, or otherwise weakens; lift check valves work well for pumping systems with high flowrates and velocities.
- Silent: Sometimes called poppet check valves, silent check valves can close prior to the reversal of flow, avoiding shocks to the system. By closing efficiently and quickly, silent check valves keep surrounding materials from being damaged.
- Swing: This self-activating check valve serves to prevent backflow or as a one-way directional valve. It features a disk that swings on a hinge to allow flow; once flow stops, it swings back into place to prevent reverse flow.
- Tilting disk: With a pivot point at the disk’s center, this check valve enables fluid to flow over and under the disk; with a center of gravity near the pivot point, the valve’s slight and lightweight disk remains open due to flow velocity, while it handles both higher pressure drops for high flowrates and lower pressure drops for low flow rates.
- Wafer: This type of check valve contains a thin disk that swings open to allow flow in one direction or closed to prevent backflow in the other direction. It often features a lever or spring connected to the disk to close the valve more quickly. With their compact design, wafer check valves work well with systems that transport solids and semi-solids or for smaller piping systems.
Types of pressure relief valves include:
- Balanced bellows: With a bellows that effectively balances and handles changing back pressure, these pressure relief valves are more expensive than more basic spring-loaded valves, though possible damage or wear to the bellows can be an issue.
- Diaphragm-type: Though the diaphragm is prone to damage and these valves generally cost more, the balanced design of these quick-opening pressure relief valves allows it to seamlessly handle most liquids.
- Membrane: With a cylindrical metal body, this pressure relief valve features a membrane made from elastic that enables instant balancing of pressure, while a counterweight keeps the valve closed when conditions fall within a normal range; membrane pressure relief valves for applications where precise pressure control is needed, such as in chemical processing, pharmaceutical and water treatment systems.
- Nozzle type: Used for pumping systems that must pump liquids with higher rates of contaminants, these pressure relief valves don’t clog easily. However, they’re also more expensive and require more maintenance due to their greater complexity.
- Pilot-operated: Able to handle considerable pressure and quick cycling conditions, the complexity of pilot-operated pressure relief valves is more costly and requires more maintenance. However, they offer precision control over set pressure.
- Piston-type: Capable of handling extremely high pressures, the complex design of piston-type pressure relief valves enables extraordinary accuracy for set pressures, though these valves are also prone to erosion and wear so that they may require more maintenance.
- Spring-loaded: Suitable for a wide array of applications, spring-loaded pressure relief valves' simple yet reliable design requires no external power. However, they can’t handle extremely high pressures and are sensitive to blockages caused by back pressure.
- Temperature-activated: As per their name, these pressure relief valves activity when temperature rises to a certain point, so they are well-suited for pumping systems where heat buildup is an issue; temperature-activated pressure relief valves need no external power source, though a downside is their slower response time to spikes of pressure.
When considering whether to use a check valve vs. pressure relief valve, it’s important to understand that some valves can be used as either a check valve or pressure relief valve. This depends on their application, though many valves are also used to regulate pressure and support other valves. Now, let’s look at how both check and pressure relief valves handle a few different applications.
Bitumen Manufacturing: Check Valve vs. Pressure Relief Valve
Bitumen mixing pumps transport unadulterated fluid without filler. Bitumen, an oil-based, viscous liquid used in paints and waterproofing, is also commonly used for roads, referred to as asphalt. Because of its viscosity at lower temperatures, bitumen requires heating to make it more flowable. For this reason, these pumps need a heat source to keep the bitumen from condensing within the pump. Pumps used for bitumen apply the principle of positive displacement and are typical of the gear or screw varieties.
Both ball, butterfly, swing, and other types of check valves can be used in asphalt and bitumen manufacturing facilities, whereas membrane pressure relief valves are also used. Membrane pressure relief valves deal with excess pressure within the silo instantly, acting as a last means of protection against anomalous pressure conditions. In bitumen processing, it’s not a question of using a check valve vs. pressure relief valve, but rather a matter of using both types of valves to ensure proper processing and safety.
Chemical Processing: Check Valve vs. Pressure Relief Valve
Industrial pumps used in the chemical processing sector can be centrifugal or positive displacement. Diaphragm and turbine pumps are the two most used positive displacement pumps for processing chemicals. Positive displacement pumps help mitigate pressure within the system, typically using a series of check valves for the chemical injection process to prevent backflows. This augments production decreases the chance of corrosion and separates mixtures to increase efficiency.
Pressure relief is particularly important for these applications as well, including for:
- Component wear: Machinery wears out over time, especially when exposed to aggressive and corrosive chemicals, which in turn may cause a problem with pressure control.
- Contamination: Particulates in fluids can result in unwanted pressure, particularly in high-pressure systems and often resulting from a compromised regulating seal.
- Human error: This may result from improper calibration, installation of an incorrect pressure regulator or opening a valve inadvertently that causes pressure to rise downstream.
- Power loss: Certain pumping systems require electric power to control specific components, which can compromise their regular functioning.
- Toxic substances: Often with toxic chemicals, excess pressure can’t be released into the environment but must be captured.
Ball and butterfly valves are two commonly used check valves in chemical processing. Globe valves are usually used in high-pressure conditions as either a check valve or pressure relief valve. Diaphragm valves can be used both to control the flow of fluid and to relieve pressure.
Oil & Gas Industry: Check Valve vs. Pressure Relief Valve
A wide variety of pumps are used for applications involving oil and gas exploration or production, as well as processing of petrochemicals. As per most industries, centrifugal pumps, along with various positive displacement pumps like diaphragm, gear, oil transfer, progressive cavity, and reciprocating plunger pumps, are most commonly used. Many different types of check valves and pressure relief valves are also used in the sector, including injecting fluids into oil and gas pipelines and unloading and loading bulk liquids. One of the most important functions of valves in this industry involves preventing excess pressure that can lead to explosions, which can damage machinery and harm or even kill workers.
Check and pressure relief valves are used for the following in the oil and gas industry:
- Controlling flow: Often used to stop or continue the flow of oil or gas through pipelines, valves at this point help prevent problems in refineries, such as from leaks or overpressure.
- Isolating equipment: While necessary during maintenance, isolating equipment in refineries can help prevent accidents, leaks, and other serious problems as well.
- Leak mitigation: In conjunction with isolating equipment, check valves prevent fluids from reversing by closing or sealing the flow between pipes, thus preventing leakage.
- Pressure relief: Potentially deadly, pressure buildup in refineries is the singularly most important function of pressure relief valves in this sector, as it may lead to an explosion.
Ball, butterfly, and globe check valves are most commonly used to transport oil, gas, or their derivatives. The oil and gas sector check valves are primarily used to protect mechanical equipment. Diaphragm and pilot-operated pressure relief valves are often used to relieve pressure.
Food and Beverage Sector: Check Relief Valve vs. Pressure Relief Valve
Pumps that are easy to clean and resist contaminants are necessary for the food and beverage industry. Single-stage and dual-stage centrifugal pumps and axial and mixed flow pumps are used in the sector. In contrast, those that work on the positive displacement principle, like diaphragm, gear, lobe, peristaltic, and piston pumps, are also commonly used. Cleanliness in this industry is key, with valves playing a prominent role in cleaning systems for processing machinery. When looking at the different applications of check valves vs. pressure relief valves in the industry, it all comes down to steam.
For industrial steam, globe or other check valves are often used. This steam is used for generating heated water for boiling pots and other similar purposes, although they’re also used for heat exchangers. Pressure relief valves are also used as a safety valve for industrial steam, and they regulate steam pressure for blanching as well. Cleaning operations in the industry often use sanitized culinary steam, where pressure relief valves feature in clean-in-place (CIP) systems that operate much like a power washer. Check valves with electropolished interiors condition hot air for processing purposes, particularly for drying food in conveyor dryers. As this air may come into direct contact with food, it must also be clean.
Pharmaceutical Pumps: Check Relief Valve vs. Pressure Relief Valve
Pharmaceutical pumps and valves require hygienic designs. Diaphragm pumps are often used in pharmaceutical pumping systems for applications like chromatography and fluid injection into extruders. Meanwhile, piston pumps are frequently used for various biopharmaceutical processes, and rotary pumps are usually used to transport highly viscous fluids. Centrifugal, booster, and other pumps are also used depending on the application.
Ball, butterfly, globe, and other check valves are all used within pharmaceutical pumping systems. Like the food and beverage industry, pressure relief valves for the pharmaceutical sector are used in pipelines, reactors, steam systems, and tanks and with potentially hazardous substances used to manufacture medications. Pharmaceutical manufacturing facilities don’t need to consider a check valve vs. a pressure relief valve for an application, but other valves are needed to maintain proper pressure within the system.
Polyurethane Manufacturing: Check Relief Valve vs. Pressure Relief Valve
Pumps are used similarly to those for the chemical processing industry for manufacturing polyurethane and other types of resins. For example, to make polyurethane foam, isocyanate combined with water and a catalyst assists with the treatment of polyether, along with fillers and agents for dispersing and emulsifying, which causes the resin to foam. Magnetic coupling pumps – a type of centrifugal pump – are often used in polyurethane manufacturing, while gear pumps are also used.
