H2X TOOLS
Pipe Velocity Calculator
Water flow rates are measured by the volume of water passing per unit of time. The water flow rate, along with the pipe diameter can be converted to a velocity using a pipe velocity calculator.
What is the Pipe Velocity Calculation Used For, and Why is it Important?
Pipe velocity is the speed at which fluid flows through a pipe and is usually measured in terms of m/s or ft/s.
It’s important to know what your pipe velocity is because it relates closely to frictional losses. The higher the velocity of a fluid, the higher the friction loss is.
High friction loss affects the pump’s performance, as well as other related equipment, which might mean you have to opt for bigger pumps.
Larger pumps and equipment can increase the capital cost of the building and also increase the operational cost to run the building. So this calculation is vital when designing a system.
The Imperial Equation
The following equation can be used to calculate the pipe velocity:
V = 0.408 Q/D
2
Components of the Equation
V = Water velocity inside the pipe (ft/second)
Q = Water flow rate inside the pipe (GPM)
D = Pipe inside diameter (inner diameter) (in)
The Metric Equation
The following equation can be used to calculate the pipe velocity:
V = 1.274 Q/D
2
Components of the Equation
V = Water velocity inside the pipe (m/second)
Q = Volume flow (m³/second)
D = Pipe inside diameter (inner diameter) (m)
Pipe Velocity Calculator
As the pipe velocity calculation can be measured in ft/second and m/second, there are two different calculation methods to establish pipe velocity:
Imperial pipe velocity calculator
Water Flow Rate
The flow rate of the fluid is the volume of fluid that passes through an area in a unit of time. It is measured in m³/s, GPM, or l/s and is directly proportional to the pipe flow velocity.
Pipe Internal Diameter
There is an inverse relationship between the internal diameter of a pipe and the pipe velocity. This means that the water velocity will increase as the pipe diameter decreases.
NOTE
There can be a difference between the values spreadsheet and values in the H2X result due to the rounding up of multiple decimal places within the calculation. The difference generally occurs by the third decimal place in the flow velocity result.
Using Our Pipe Velocity Calculator
This free spreadsheet contains the pipe velocity formula that is used for the H2X calculations. The spreadsheet calculates the water velocity if you have the following variables available:
Flow rate
Pipe diameter
PIPE VELOCITY CALCULATOR VARIABLES:
Pipe Diameter and Water Flow Rate
As shown in the calculations below, pipe velocity depends on two main factors:
The water flow rate
The pipe diameter
The objective behind creating H2X was to use modern technology combined with recognised methods of plumbing engineering to automate plumbing calculations, so you can save hours designing each project while reducing errors, rework, and costs.
Using H2X, you won’t need to use a pipe velocity calculator as the process is streamlined.
The process that you follow when using H2X is:
Set the parameter for maximum velocity
Draw the pipe layout
The flow rate is calculated based on how many fixtures are connected to the pipe.
The pipe size is calculated using the mass flow rate and maximum velocity parameter.
The pressure drop through the pipes, valves and fittings can then be calculated
How Can H2X Simplify Manually Calculating the Pipe Velocity?
Besides the fact that manually calculating pipe velocity is a time-consuming process, any manual calculation opens up the doors for human error.
FAQs
What pipe velocity should I design to?
This depends on the following variables:
The local standard
For example, pipes are generally designed to higher velocities in the USA compared to the UK
The pipe material
For example, stainless steel pipes can generally be designed to higher velocities than copper pipes
If the pipe is above a habitable space
For example, if the pipe is above a room such as a bedroom, the pipe velocity should be kept low to avoid unwanted noise. Whereas, a pipe in a factory could be designed to a higher velocity.
The application
For example, pipes containing hot water in recirculating systems should be designed to a lower velocity than cold water pipes
Typical water velocity in a pipe is generally between 0.7-2.4 m/s. Typical velocities are:
Velocities should not go lower than 0.7m/s as this is required to maintain a self-cleansing velocity. For example, if liquids contain solid particles, engineers try to achieve a higher velocity so that the heavy particles in the liquid don’t settle and cause blockage in the pipe.
Hot water return velocity - 0.7-1m/s or 2-3 ft/s
Hot water flow velocity - 1.2-1.5m/s or 4-5 ft/s
Cold water velocity - 1.5-2.4m/s or 5-8 ft/s
How does velocity affect equipment life?
The right velocity will allow the system to run smoothly for longer periods. This will also save on maintenance costs.
Laminar or turbulent flow?
If the pipe velocity is high, the fluid flow will be called turbulent flow. With a turbulent flow, there is no smoothness in the process. Instead, the pipe experiences random mixing. A turbulent flow results in an increased head loss (or pressure drop) and causes extensive wear to the pump and other parts as well.
Similarly, if the pipe velocity is low, the fluid flow is known as a laminar flow. With a laminar flow, a regular and consistent fluid flow is witnessed throughout the pipe. Laminar flow would provide improved overall system efficiency.