Appropriate sizing is important for all components of your air compressor system, including hose sizes. If you are investing in an air compressor system, restricting the flow anywhere in your system can make it significantly underperform or require unnecessary energy costs to run that compressor over its lifetime.

As air travels from the compressor head to your tool, it travels through components such as hoses, fittings, valves, and tanks. Each of these components will restrict the flow of air in some way, depending on the geometry of each component and the magnitude of the flow passing through it.

For example, a 100 foot, 1” hose delivering 100 CFM at 90 psi will result in a 3.35 psi pressure drop. If that same hose is tripled to 300 feet, the pressure drop is 10.1 psi, which means the air is now pressurized to only 80 psi.

As a result, your compressor is working harder and using more power than it should to keep up with your air demands, or—if it can’t keep up—your tool performance will be reduced. In some cases, where power at the tool is important, you may not be able to complete your work.

Quick calculators or charts, such as those found at can be used to calculate the pressure drop in any of your pipes or components. When sizing your air compressor, consider each of the following components:

- Hose reels
- System piping/tubing
- Filters
- Regulators
- Lubricators
- Fittings

Components such as filters will often have pressure , so be sure to check the documentation and specifications carefully to match components to the system.

When considering fittings and quick connects, work with your suppliers to ensure they are rated for the maximum pressure your compressor system is rated for and will not cause excessive pressure drop at the required flow rates.

## How Fittings Cause Pressure Drops

Pressure drop is due to the restriction created by the pipe or fitting. Anyone who has tried to breathe through a drinking straw can tell you that trying to force a large flow of air through a small hole can be difficult. This is because the smaller the diameter, the higher the velocity is required for the air to travel through the hole.

Higher velocities result in more friction created due to boundary layers at the walls of the pipe or fitting creating more losses. With pipes and hoses, the loss is by the length of the pipe. Consider the reduced diameter of the pipe with the fitting when doing pressure drop calculations.

It can be surprising how small the flow diameter is in some fittings. A quick-connect fitting is one of the worst culprits. Next time you are looking at a quick connect, look inside to see how small the actual flow area is.

## Calculating Pressure Drop of Fittings

Pressure drop can be calculated for some components and is made even easier by online tools such as this one. Note that this calculator is for hard pipe as it is a well-defined shape. Flexible hose in actual use typically contains many bends and loops and as such it is not possible to create an accurate generic calculator. While flexible hose will have more losses than a pipe with an identical inside diameter, we can still use the pipe loss calculation to get an estimate and see the influence diameter has on pressure loss.

Let’s look at some examples.

To illustrate the dramatic difference that pipe or hose diameter makes on pressure loss, let’s use this tool to compare 100ft long pipes with internal diameters of ½”, ¾”, and 1”. In this example, we have 70 CFM FAD (free air delivery) of compressed air, delivered at 100 PSI gauge pressure (equivalent to 114.7 PSI absolute pressure*) at the upstream hose entrance.

The approximate pressure loss from end to end for the three pipe sizes is:

1″ x 100’: ~1.4 PSI pressure loss

3/4″ x 100’: ~5.7 PSI pressure loss

1/2″ x 100’: ~44 PSI pressure loss

Your compressor would have to be operating at a constant, ~134 psi gauge pressure† to maintain 100 psi at the tool with the ½” pipe.

## Increasing Pressure vs. Increasing Supply Line Size

Increasing the pressure of your compressor to compensate for flow losses can have a dramatic impact on the amount of work your compressor system is doing. Conversely, increasing the size of the supply lines can provide the following benefits:

- Less fuel/energy used by your compressor
- Less heat generated by the compressor
- Longer oil life and service interval
- Lower noise output from the compressor
- Improved safety due to lower operating pressures and lower temperatures
- Lower load on drive system components
- Less wear and longer life of your compressor

Each restrictive fitting, hose, accessory, and bend added to your system results in cumulative pressure drop and can negatively affect the performance of your tool or equipment. Recognizing this and planning and sourcing the right sized components will enable your air system to perform better.

As always, keep in mind that formulas and calculators like the one used above are just a guide. Real-life scenarios depend on many factors, and each will affect your individual results. Using a larger diameter hose may cost more, but it can result in long-term savings and may even allow for a lower pressure or output compressor, saving money upfront.

***Absolute pressure is the pressure relative to a perfect vacuum. Gauge pressure is relative to atmospheric pressure. Standard atmospheric pressure is 14.7 PSI so for a calculation such as this one, which requires absolute pressure, atmospheric pressure (14.7 psi) needs to be added to your gauge pressure.

† Note that it may seem that the entrance pressure would need to increase by the same pressure as the loss in the pipe from the first calculation. However, the increase is slightly reduced. As the pressure increases, the volume flow and flow velocity decreases (for the same air mass), and therefore the pressure drop decreases as well.