Pressure relief valves are vital safety devices used in a variety of machines. These devices depend on pressurized vessels or are themselves pressurized systems used to protect during times of overpressure, especially with hydraulics and liquid service machines. Many devices rely on pressure relief valves, such as brakes, pilot lines and hydraulic cylinders. These instruments perform this task by automatically opening further when the pressure increases and closing when the pressure returns below its opening pressure.

There are three main types of pressure relief valves. Understanding where and how they operate will help when searching for the right valve for your machine.

Water Pressure Relief Valves

Water pressure relief valves are often used by private and municipal water supply companies. These machines are used in pumps for a variety of different reasons including—but not limited to—firefighting, high-rise buildings, water towers, drinking water applications and water tanks.

All of these outlets are vulnerable to high water pressures — those that exceed 200 pounds per square inch (psi). High pressure can damage machines and harm the workers using them. Water pressure reducing valves work with the devices above and remove excess pressure by opening up, thereby minimizing the pressure. Other characteristics of water pressure relief valves include:

• Made up of metallic bodies, of cast iron or brass.
• Range from 10-70 to 0-50 psi and many more variations.
• Can withstand high temperatures of up to 300 degrees Fahrenheit.
• Available in different lengths, widths and pipe sizes to accommodate a variety of machinery.

Hydronic Pressure Relief Valves

Hydronic pressure relief valves are a series of varied pressure relief valves used for hydronic applications. These applications involve hydronic systems, which transfer hot water through various machines and appliances. Hydronic systems take the outlet forms of radiators, baseboards, radiant tubing and heating devices like boilers and forced air systems.

Without hydronic pressure valves being interconnected between these systems, a residence or workplace would not be adequately heated, if at all. By maintaining a steady minimum pressure, these valves serve as a hydronic system’s safety net. Hydronic pressure valves provide relief in that they assist in pressurizing these systems, keeping the pressure to a minimum, which is generally 4-to-5 psi inch gauge. Here are some more water hydronic pressure valve characteristics:

• Made in a wide variety of models, sizes and metals like cast iron, forged brass and stainless steel.
• Subtypes include motorized electronic valves, combination/strainer ball valves, two-way globe valves, flow control valves and many others.
• Are fit for geothermal systems, actuator motors, terminal boards and more.
• Have the ability to operate during a power failure.

Back Pressure Valves

Back pressure valves are pressure regulator valves used in pipes and pumps. They are essential in the plumbing industry. Their function is to maintain a set pressure, particularly at the pump’s outlet port or discharge, and doing so ensures correct metering.

This very action of back pressure relief valves is also used to thwart siphoning. Back pressure valves are defined by their construction, which is usually made up of closed valves located at the end of a system of pipes. Using this form, back pressure valves create a barrier that blocks off excess flow. This kind of regulation controls upstream pressure, which is also called back pressure. This relief is particularly needed during low-pressure injection pumping below tank level. Here are a couple of other back pressure valve characteristics:

• Available in brass, cast iron, bronze and other metals often with multi-functioning valves.
• Obstructing the pressure can aid the contents before the valve, like the contents of a tank at the end of a return line.
• Resourceful back pressure valves ought to obstruct all the parts behind it. Obstructing the extra pressure creates an environment of sufficient pressure, allowing the tank or pipe to run smoothly.
• During times of high pressure, back pressure valves open and dump excess into the tank.

Choosing Pressure Relief Valves

Pressure valves are one of the two types of pressure relief systems, the other being rupture discs. Rupture discs are increasingly used with pressure relief valves because the grouping of them yields many benefits. A pressure relief valve is a key component within various industries like plumbing, construction, engineering, hydraulics and others. It's the primary difference in an over-pressurized system that can damage both equipment and entire operations, as well as in a properly running pressurized vessel. Knowing what kind of devices are out there and what they do will help you choose the best instrument for your facility.