With pipe diameter calculator pipe internal diameter is calculated using the simple relation between flow rate, velocity and cross-section area (Q=v·A).

There’s often confusion about whether National Fire Protection Association (NFPA) standards require backflow preventers on fire protection systems. Let’s be clear: they do not.

603.5.14 Except as provided under Section 603.5.14.1 and Section 603.5.14.2, potable water supplies to fire protection systems that are normally under pressure, including but not limited to standpipes and automatic sprinkler systems, except in one – or two-family or townhouse residential sprinkler systems, piped in materials approved for potable water distribution systems shall be protected from backpressure and backsiphonage by one of the following testable devices:

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RPZ assemblies also feature two independently operating check valves. However, they add another layer of protection that makes them essentially fail-safe by also locating a hydraulically operated differential relief valve below the first check valve.

PVBBackflowPreventer

Task: Calculate the diameter of the carbon dioxide pipe with a flow rate of 10 kg/h and a velocity 2 m/s at a pressure of 7 bar absolute and a temperature of 20 °C.

This calculator has an almost limitless application, but some functionalities are dependent on several conditions.

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City water mains provide water for most homes and buildings, including the water used in fire protection systems. But the stagnant water that fills the pipes of wet fire protection systems is “non-potable”—it’s not fit to drink. Thus, water authorities often require property owners to install backflow preventers to keep stagnant water from mixing with the treated, “potable” water in the city water supply.

The mass conservation law is applicable only if the stream is in the closed pipe, without added or subtracted flow, if the flow is not changing in time and a few other conditions. Read more about mass conservation of mass.

Several types of backflow preventers exist, and each is intended for specific applications. The most common assemblies include:

Read all about available deployments. In any way of utilizing calculator, Internet connection is not required, but nice to have for authentication at least.

You have to know the density of the liquid if the mass flow rate is available instead of the volume flow rate. If the density of the liquid is unavailable, and only the mass flow rate is known, then the volume flow rate required for pipe diameter calculation is not possible.

If the flowing fluid is gas, then instead of density, you have to know gas constant, absolute pressure, and temperature. Density is calculated using the equation for the perfect gas.

Task: Calculate the pipe diameter if the water flow velocity is 1 m/s and the flow rate is 5 lit/min.

Potable water supplies to fire protection systems that are not normally under pressure shall be protected from backflow and shall be in accordance with the requirements of the appropriate standards referenced in Table 1701.1.

For a calculation of the pipe diameter with this calculator, you should know and enter the flow velocity. It the flow velocity is unknown then you have to use the pressure drop calculator to calculate pipe diameter. You can use pressure drop calculator when the pressure difference between the start and the end of the pipeline (head loss) is available as a known value.

Conversion between mass and volume flow rate is available for given fluid density. Also, for perfect gases, volume flow rate conversion for different flow conditions (pressures and temperatures) is possible, so you can quickly calculate the volume flow rate on specific pressure or specific temperature in the pipe, like after pressure reducing valves.

If flowing fluid is perfect gas, you can calculate volume flow rate of that gas at different pressures and temperatures. For example, if you know volume flow rate of some ideal gas at some predefined pressure and temperature (like at normal conditions p=101325 Pa and T=273.15 K), you can calculate actual volume flow rate for pressure and temperature that is actually in the pipe (for example, the real pressure and temperature in the pipeline is p=30 psi and t=70 F). Volume flow rate of the perfect gas is different at these two conditions. Read more about normal conditions for pressure and temperature.

Such potential health dangers are alarming, but they aren’t the only problem. Backflow can also be extremely expensive to remediate. The Environmental Protection Agency (EPA) states that the average backflow incident takes nearly 500 hours to fix at a cost of $14,800.

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You can use pipe diameter and flow rate calculator for quick pipe diameter calculation in a closed, round, rectangle (online calculator version only) and filled pipes with liquid or perfect gas.

For those reasons, the model code often treats fire protection systems with FDC connections as high-hazard situations for backflow.

Backflow preventers are otherwise required in many fire protection systems, however. Mandates for installing backflow preventers are set forth by local plumbing codes developed and enforced by organizations like municipalities, water purveyors, and plumbing inspectors to protect local drinking supplies.

Some jurisdictions also allow alternatives to backflow preventers. For instance, Philadelphia’s water district requires all residential systems supplying dedicated sprinkler heads to have a connection from the sprinkler system to the toilet tank that’s farthest from the water supply. This removes the need for a backflow preventer, because every time that toilet is flushed, it draws water through the fire line to keep the water fresh.

However, UPC model code requires stand-alone residential systems using non-potable piping materials to achieve the same level of protection as a commercial system. Increased protection is also required when chemicals are added to a fire protection system supplied by a potable water supply.

Important: File with the solution for this task can be opened with Pipe flow calculator which you can download separately here:

Touted as the most complex and reliable backflow preventers, RPZ assemblies are primarily intended for a building’s internal systems like plumbing or fire protection. In fire protection systems, they are most commonly used when hazardous chemicals like antifreeze or corrosion inhibitors are introduced—although some municipalities require RPZs on all fire protection applications.

603.5.14.2 Where antifreeze, corrosion inhibitors, or other chemicals are added to a fire protection system supplied from a potable water supply, the potable water system shall be protected by one of the following:

With this calculator, you can convert volume flow rate from standard or some other predefined conditions to actual conditions and vice versa. The calculator uses the mass conservation law for computation of volume flow rates for this two conditions, meaning that mass flow is constant, despite that conditions, like pressure and temperature are changing.

The model plumbing code also requires backflow preventers on fire department connections (FDC) located less than 1,700 feet (518.2 m) from a non-potable water source that might be used by the fire department.

To calculate pipe diameter, you have to know flow velocity and flow rate. If you know mass flow rate, then fluid density has to be known.

Be sure to check out our selection of Backflow Check Key Tools and Tool Sets that quickly and painlessly remove or install cam checks found in Ames and Watts backflow prevention assemblies.

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As mentioned above, pipe diameter calculation with this calculator is not possible if you are not sure about flow velocity and volume/mass flow rate. If any of these two are missing, then you should use pressure drop calculator.

For gas flow, the equation for perfect gas is used to calculate density from gas constant, absolute pressure, and temperature.

The American Water Works Association (AWWA) supports model code requirements by offering guidance for when backflow preventers should be installed based on the degree of hazard presented by a fire protection system. A low-hazard cross-connection might create a nuisance or would be aesthetically objectionable if there is a backflow incident but would not create a health hazard. An unprotected high-hazard cross-connection is a health hazard, involving any substance that could cause death or illness or spread disease if it is introduced into the city’s water supply.

Double CheckBackflowPreventer

In wet fire protection systems like certain types of sprinklers or standpipes, a large volume of water never moves until it flows from an activated sprinkler head or a broken sprinkler pipe. When water is stagnant, bacteria can fester—transforming the sprinkler water into a thick, smelly, black, oily sludge that could potentially cause serious issues if it reverses into a city’s drinking supply.

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Backflow preventers are required in fire protection systems by the 2018 edition of the Uniform Plumbing Code, the model code developed by the International Association of Plumbing and Mechanical Officials (IAPMO) to promote the public’s health, safety, and welfare by governing the installation and inspection of plumbing systems.

DCABackflowPreventer

For perfect gases, the density of the fluid is not mandatory, if you know the pressure, temperature and gas constant for the flowing gas. The calculator uses the perfect gas equation for density calculation. However, if the flowing fluid is gas but not a perfect (ideal) gas, i.e., if it's pressure, temperature and density are not related according to ideal gas law, this calculator is not applicable if you are trying to calculate that gas density for known pressure and temperature.

While fighting a fire, firefighters are understandably more concerned about drawing enough water to douse the blaze than backflow prevention. Not only will they use water from any available source to achieve their goal, but fire department vehicles often carry non-potable water treated with antifreeze, corrosion inhibitors, or extinguishing agents.

Calculation of pipe diameter with the pipe diameter calculator is easy. You can use pipe diameter and flow rate calculator for quick pipe diameter calculation in a closed, round, rectangle (online calculator version only) and filled pipes with liquid or perfect gas.

Pipe diameter and flow velocity calculation use the continuity equation that gives the relation between flow rate, flow velocity, and interior pipe diameter.

These organizations view backflow prevention through the broad lens of the overall community need—and recognize that every cross-connection between a wet building system and city water has the potential to trigger a serious backflow event. Water purveyors also typically require backflow preventers to be tested regularly and maintained by certified professionals to ensure they are reliable and functioning properly. It is important to check with your local water authority to understand specific requirements for backflow preventers in your area.

backflowpreventer中文

In fact, reverse flow testing designed to ensure that backflow preventers prevent backflow was removed from NFPA 25 in 2011. While NFPA recognizes that backflow remains a legitimate health concern, it considers preventing it outside the scope of NFPA 25. Instead, NFPA presumes that local or state requirements will ensure that backflow preventers are properly tested by qualified personnel.

603.5.14.1 Where fire protection systems supplied from a potable water system include a fire department (Siamese) connection that is located less than 1700 feet (518.2 m) from a non-potable water source that is capable of being used by the fire department as a secondary water supply, the potable water supply shall be protected by one of the following:

On a fire protection system, backflow preventers rely on two one-way valves, or check valves, assembled in a series to prevent water from backing up into the supply line. Think of the check valves as one-way gates, only allowing water to flow through them in one direction.

RPZs expand upon the double check valve concept with a hydraulically operated relief valve that makes them virtually foolproof. They typically consist of an inlet shutoff valve, two spring-loaded check valves separated by a pressure differential relief valve, four test cocks, and an outlet shutoff valve.

It’s important to understand that RPZ assemblies, while more reliable, experience much higher pressure and volume loss than double-check assemblies. Fluctuations in line pressure, upstream or downstream, will prompt a properly functioning RPZ assembly to periodically discharge small amounts of water. During a backflow condition, a large volume of water will flow from the relief valve. For this reason, RPZ assemblies shouldn’t be installed in areas subject to water damage. Adequate drainage must also be provided.

Task: Calculate the airflow velocity if the inner diameter of the pipe is 50 mm and the flow rate is 100 m3/h at a pressure of 3 bar absolute and a temperature of 15 °C

If the system that you are analyzing has more than one pipe, you can use pipe network analysis calculator

What are the four types ofbackflow preventers

Sprinkler systems connected to non-potable public water supplies or alternative sources of water can still pose contamination risks if the potential for a cross-connection exists to a city’s drinking water. Backflow from systems that contain antifreeze or other chemicals such as foam is also a serious concern.

WattsBackflowpreventer

PVB assembles, intended for lawn irrigation, are the least expensive type of whole-system backflow preventer. They are relatively simple in design and the easiest to install, maintain, and repair.

While UPC does differentiate between residential and commercial systems, its leniency only applies to residential systems using potable water piping materials. In one- and two-family dwellings, AWWA states that backflow preventers are not needed on sprinkler systems constructed of approved potable material and designed to flow water, so it doesn’t stagnate. Instead, backflow requirements for domestic plumbing could apply to those sprinkler systems.

Make sure to check with your local authority having jurisdiction (AHJ) on the exact backflow prevention requirements for your area, system, and occupancy type.

Approved backflow assemblies have met the requirements of different approved testing agencies such as the American Society of Mechanical Engineers (ASME), the American Society of Sanitary Engineer (ASSE), the American Water Works Association (AWWA), the American National Standards Institute (ANSI), the Factory Mutual Research Corporation (FM), and UL (formerly Underwriters Laboratory).

If the flowing fluid is gas, then instead of density, you have to know gas constant, absolute pressure, and temperature. Density is calculated using the equation for the perfect gas.

The double check assembly was developed in the 1950s for the fire protection industry, creating a redundancy designed to ensure that one check valve will continue to protect the city water supply even if the other fails. This assembly also enables the closure of one valve to reduce the pressure differential across the other, creating a more reliable seal and avoiding even minor backflow leakage. Test cocks, or small ball valves, enable the attachment of testing equipment that evaluates whether the double check assembly is functional.

If you need to maintain a backflow preventer in your fire protection system, be sure to check out our selection of Backflow Check Key Tools and Tool Sets. They painlessly remove or install cam checks found in Ames and Watts double check and reduced pressure zone backflow prevention assemblies.

Water that enters a home or building’s fire protection, plumbing, or irrigation system from a main water supply line should only flow in one direction: into the property. But sometimes, pressure changes in the pipes can cause water to seep back into the main supply line.

It’s also essential to note that both types of backflow preventers reduce available downstream water pressure. A knowledgeable contractor must account for this when designing fire protection systems.

Other values, besides internal pipe diameter, can be calculated as well. You can calculate flow velocity for the given fluid flow rate and internal pipe diameter. As velocity is different on different places of pipe cross-section area, flow mean velocity is computed based on the continuity equation.

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RPZBackflowPreventer

Any time the pressure on the property (downstream) side exceeds the pressure on the city side, the two redundant check valves close—preventing any backflow. However, while DCV systems are considered safe for most fire protection systems, they do have a flaw: if both valves fail or debris in the water line prevents them from closing completely, backflow can occur.

DCVs are specifically designed to prevent backflow in fire sprinkler systems. The mainstay for normal fire protection applications, DCVs feature an inlet (upstream) shutoff valve, two independently operating spring-loaded check valves (usually inside a single valve body), four test cocks, and an outlet (downstream) shutoff valve.

Backflow is dangerous because it can pollute the public drinking supply with contaminants like fertilizers, pesticides, human waste, and harmful chemicals. In 2010, for example, students at a Bowling Green, Kentucky elementary school suffered nausea and other symptoms after a contractor working on the HVAC system caused the antifreeze chemical glycol to backflow into the school’s drinking supply.

Backflow from fire protection systems can threaten the safety of potable water. Understanding how backflow preventers work and why they are important in a home or business helps property owners prevent avoidable accidents—and meet code requirements in their area.

Requirements in NFPA 13: Standard for the Installation of Sprinkler Systems for installing backflow preventers and in NFPA 25: Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems for performing annual forward flow tests are sometimes perceived as a mandate to have them. But the intent of the code is to only attach installation and ITM requirements to systems where backflow preventers are present.

Types of irrigationbackflow preventers

For instance, a water-main break or the opening of a fire hydrant can cause water pipes to lose pressure. When that happens, water is no longer pushed forward into the property, enabling it to flow backward into city water supplies.

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For a calculation of the pipe diameter with this calculator, you should know and enter the flow velocity. It the flow velocity is unknown then you have to use the pressure drop calculator to calculate pipe diameter. You can use pressure drop calculator when the pressure difference between the start and the end of the pipeline (head loss) is available as a known value.

Here’s how it works: During normal operation, the pressure between the two check valves—referred to as the zone of reduced pressure—is maintained at a lower pressure than the supply pressure. If either check valve should leak, the relief valve is designed to open and discharge water to the outside, ensuring backflow never occurs.

A backflow preventer is a device designed to keep water inside fire-protection and other water-based systems on a property—ensuring it only travels in one direction: from the water main into the system’s pipes.

To calculate flow velocity, you have to know flow rate and pipe interior diameter. If you know mass flow rate, then fluid density has to be known.

To calculate internal pipe diameter, you should only enter flow rate and velocity in corresponding fields in the calculator and click calculate button to get results.

In commercial applications, for instance, AWWA M-14: Backflow Prevention and Cross-Connection Control Recommended Practices recommends a DCV assembly on wet or dry sprinkler systems unless there is a risk of a high-hazard cross-connection. In those cases, an RPZ assembly is suggested.