Tag: pressure drop

Compressed Air and Pressure Drop: Explained

Published on by Tyler DanielLeave a comment

A critical component to optimal performance of any compressed air operated product is ensuring sufficient compressed air flow. Simply put, inadequate air flow won’t allow you to get the job done.

 As compressed air moves through the distribution system, it encounters friction inside the walls of the pipe, tube, hose, etc. The diameter of the pipe, length, number of direction changes, and finished surface of the inner wall all play a part in this. A drop in air pressure will occur as a result of this friction. In addition to pressure drops experienced due to the distribution system, they can also occur at the point of use. If the line is undersized, this pressure drop will be great enough to impact the performance of the product. 

When designing and maintaining your compressed air system, pressure measurements should be taken at varying points to identify (and fix) any issues before they create a greater problem down the road. According to the Compressed Air Challenge, these are the places you should take regular pressure measurements to determine your system operating pressure:

  • Inlet to compressor (to monitor inlet air filter) vs. atmospheric pressure
  • Differential across air/lubricant separator
  • Inter-stage on multistage compressors
  • After-cooler
  • At treatment equipment (dryers, filters, etc.)
  • Various points across the distribution system
  • Check pressure differentials against manufacturers’ specifications. If high pressure drops are noticed, this indicates a need for service.

*More recent compressors will measure pressure at the package discharge, which will include the separator and after-cooler.

Once you’ve taken these measurements, simply add the pressure drops measured and subtract that value from the operating range of your compressor. That figure is your true operating pressure at the point of use.

If your distribution system is properly sized and the pressure drops measured across your various equipment are within specifications, any pressure drop noticed at the point of use is indicative of an inadequate volume of air. This could be due to restrictive fittings or undersized air lines, hose, or tube. Check that the point of use product is properly plumbed to compressed air per the manufacturer’s specifications.

EXAIR Products are designed to minimize this pressure drop by restricting the flow of compressed air. The more energy (pressure) that we’re able to bring to the point of use, the more efficient and effective that energy will be. The photo below shows two common examples of inefficient compressed air usage. With an open-ended blow off, a pressure drop occurs upstream inside the supply line. If you were to measure the pressure directly at the point of use, while in operation, you’d find that the pressure is significantly lower than it is at the compressor or further up the line. In the other photo with a modular style hose, some pressure is able to build up but if it gets too high the hose will blow apart. These types of modular style hose are not designed to be used with compressed gases.

EXAIR’s Super Air Nozzles, on the other hand, keep the compressed air right up to the point of discharge and minimize the pressure drop. This, in addition to the air entrainment, allows for a high force while maximizing efficiency. If you’d like to talk about how an EXAIR Intelligent Compressed Air Product could help to minimize pressure drop in your processes, give us a call.

Tyler Daniel, CCASS

Application Engineer

E-mail: TylerDaniel@EXAIR.com

X: @EXAIR_TD

Pressure Drop and Compressed Air Piping

Published on by John BallLeave a comment

EXAIR has been manufacturing Intelligent Compressed Air Products since 1983. They are engineered with the highest of quality, efficiency, safety, and effectiveness in mind. Since compressed air is the utility for operation, the performance limitations can be defined by its supply. With EXAIR products and pneumatic equipment, you will need a way to transfer the compressed air from the source to the point-of-use. There are three main ways; pipes, hoses and tubes.

One of the largest systematic problems with compressed air systems is pressure drop.  If too large a pressure loss occurs, pneumatic equipment will not have enough power to operate effectively and efficiently.  The amount of pressure drop is based on restrictions, obstructions, and piping.  When air is forced into small areas, it will cause a high velocity.  The high velocity will create turbulent air flow which increases the pressure loss.  A restrictive type of pressure drop can be found in different forms, like small diameter pipes or tubing; or restrictive fittings like quick disconnects and needle valves, and undersized filters, regulators and valves. 

Why did I bring this up? Pressure drop… Pressure Drop is a waste of energy, and it reduces the ability of your compressed air system to do work. To cut waste, we need to reduce pressure drop.  If we look at the equation for pressure drop, we can find the factors that play an important role. Equation 1 shows an equation for pressure drop.

Equation 1:

From Equation 1, differential pressure is controlled by the flow of compressed air, the length of the pipe, the diameter of the pipe, and the inlet pressure. As you can see, the pressure drop is inversely affected by the inner diameter to the fifth power. So, if the inner diameter of the pipe is twice as small, the pressure drop will increase by 25, or 32 times.

It is very important to know the inner diameter of the supply lines to your pneumatic devices.  As an example, a model 110006 6” Super Air Knife will need a 3/8″ black, schedule 40 pipe that has an I.D. of 0.493″ (12.5 mm).  We use this pipe to flow 21 SCFM of compressed air at 100 PSIG through 50 feet of pipe.  What would be the pressure drop?  With Equation 1, we get a pressure drop of 1.28 * (21 SCFM/60) ^1.85 * 50 feet / ((0.493″)^5 * 100 PSIG) = 3.15 PSID.  Thus, you started with 100 PSIG, and at the end of the 50 ft. pipe, you will only have (100 PSI – 3.15 PSI) = 96.85 PSIG to use. 

Let’s look at a 3/8” hose and a 3/8” tube. The 3/8” hose has an inner diameter of 0.375” (9.5 mm), and the 3/8” tube has an inner diameter of 0.25” (6.4 mm). In keeping the same variables except for the diameter, we can calculate the pressure drop with the above equation. 3/8″ hose = 1.28 * (21 SCFM/60) ^1.85 * 50 feet / ((0.0.375″)^5 * 100 PSIG) = 12.4 PSID. 3/8″ tube = 1.28 * (21 SCFM/60) ^1.85 * 50 feet / ((0.25″)^5 * 100 PSIG) = 94 PSID.

As you can see, the 3/8” hose has a pressure drop 3.94 times higher than the 3/8″ NPT pipe. Also, the 3/8″ tube has a pressure drop 7.6 times higher than the hose. 

Diameters: 3/8″ Pipe vs. 3/8″ tube

At EXAIR, we want to make sure that our customers are able to get the most from our products. To do this, we need to properly size the compressed air lines. Within our installation sheets for our Super Air Knives, we recommend the in-feed pipe sizes for each air knife at different lengths. (You will have to sign in to the website to download).  We also have an excerpt about replacing schedule 40 pipe with a compressed air hose. We state; “If compressed air hose is used, always go one size larger than the recommended pipe size due to the smaller I.D. of hose”. Here is the reason. The 1/4” NPT Schedule 40 pipe has an inner diameter of 0.364” (9.2mm). Since the 3/8” compressed air hose has an inner diameter of 0.375” (9.5mm), the diameter will not create any additional pressure drop. Some industrial facilities like to use compressed air tubing instead of hoses. This is fine as long as the inner diameters match appropriately with the recommended pipe in the installation sheets. Then you can reduce waste from pressure drops and get the most from your EXAIR as well as all other pneumatic products.

With the diameter playing such a significant role in creating or mitigating pressure drop, it is very important to understand the type of connections to your pneumatic devices; i.e. hoses, pipes, or tubes. In most cases, this could be the reason for the under performance of your pneumatic products, as well as wasting money through operation of your compressed air system. If you would like to discuss further the ways to save energy and reduce pressure drops, an Application Engineer at EXAIR will be happy to help you.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Compressed Air Pipe

Intelligent Compressed Air: Distribution System Design

Published on by Russ BowmanLeave a comment

No matter what kind of compressor you have, or what you use compressed air for, a critical part of your system is the distribution system. My neighbor has a 5HP reciprocating compressor that sits on top of a 50 gallon tank in his garage. Unlike me, he LIKES working on cars, and has a variety of pneumatic tools, and a really nice air operated paint sprayer that he can make a car look brand new with. Anyway, his “distribution system” is a 1/2″ rubber air hose with a quick connect on the end. And that works just fine for him.

On the other end of the compressed-air-system-complexity spectrum, a large manufacturing facility may have a few (or more) compressors, and they may not even be in the same room. Today, we’re going to look at the factors that affect distribution design, and some of the “pros and cons” of those designs.

The two main types of supply systems…centralized (where there’s one single compressor room), and de-centralized (where individual compressors are located throughout the facility). There are advantages, and disadvantages to both as far as maintenance, number of operators required, controls, utilities, and noise reduction go. The main impact of these on the distribution and storage layout falls largely on distribution design. Supply headers have to be adequately sized, and plumbed, to get sufficient air flow to the farthest usage points from a centralized compressor room. Inadequate initial design, or adding load without considering flow capacity to service added load, can lead to increasing compressor discharge pressure to keep point of use pressure at the required level. De-centralized systems aren’t usually as affected…because they’re closer to their points of use by design, there’s less pressure loss through the distribution lines.

Whether the supply side is centralized or de-centralized, the advantages & disadvantages of different distribution piping layouts are similar in nature. Let’s look at a Loop design:

In this design, the compressors feed a complete loop of piping, with drops at points of use.

Since compressed air loses pressure due to friction as it flows through the distribution piping, it’s always important to design for the distance from the compressor, to the point of use, to be as short as possible. A Loop design facilitates this by allowing the air to reach any point of use from two directions…by definition, the farthest that the air has to travel is half the total length of the piping.

The other basic style of distribution layout is called “Trunk & Branch”:

In this design, the “trunk” (the horizontal line) feeds a series of “branches” (the vertical lines) to various points of use.

If the distance from the compressor(s) to the farthest point of use isn’t excessively long, a Trunk & Branch system is a lower cost alternative, because it uses less pipe. Keep in mind that line loss will necessarily create a pressure drop that steadily increases, the farther it gets from the compressor. If that means you have to use larger pipe, your installation & materials costs start to creep right back up. The larger the facility, the more sense it makes to consider a Loop design. Alternately, a de-centralized compressor layout can minimize line loss in a Trunk & Branch design too. Locating a compressor on the right-hand side of the sketch above, for example, will effectively give you the major benefit of a Loop design: allowing air to reach any point of use from both directions.

At EXAIR, our mission is to help you get the most out of our products, and your compressed air system. If you have questions, we’ve got answers – give me a call.

Russ Bowman, CCASS

Application Engineer
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Compressed Air Distribution System, Keeping Pressure Drop to a Minimum

Published on by John BallLeave a comment

Compressed air is used to operate pneumatic systems within a facility, and it can be separated into three categories; the supply side, the demand side, and the distribution system.  The supply side is the air compressor, after-cooler, dryer, and receiver tank that produce and treat the compressed air.  They are generally located in a compressor room somewhere in the corner of the plant.  The demand side is the collection of devices that will use that compressed air to do “work”.  These pneumatic components are generally scattered throughout the facility.  To connect the supply side to the demand side, a compressed air distribution system is required.  Distribution systems are pipes which carry the compressed air from the compressor to the pneumatic devices.  For a sound compressed air system, the three sections have to work together to make an effective and efficient system.

An analogy that I like to use is to compare the compressed air system to an electrical system.  The air compressor would be considered the voltage source, and the pneumatic devices would be marked as light bulbs.  To connect the light bulbs to the voltage source, electrical wires are needed which will represent the distribution system.  If the gauge of the wire is too small to supply the light bulbs, the wire will heat up and a voltage drop will occur.  This heat is given off as wasted energy, and the light bulbs will be dim.  The same thing happens within a compressed air system.  If the piping size is too small, a pressure drop will occur.  This is also wasted energy.  In both types of systems, wasted energy is wasted money.  One of the largest systematic problems with compressed air systems is pressure drop.  If too large of a pressure loss occurs, the pneumatic equipment will not have enough power to operate effectively and efficiently.  As shown in the illustration below, you can see how the pressure decreases from the supply side to the demand side.  With a properly designed distribution system, energy can be saved; and, in referencing my analogy above, it will keep the lights on.

Pressure Drop Chart

To optimize the compressed air system, we need to reduce the amount of wasted energy.  This can be caused from leaks or pressure drop.   Leaks can be hidden and are typically located at connections within the distribution system.  In a poorly maintained system, a study found that 30% of the compressor capacity is lost through air leaks on average.  Even though leaks are the “silent killer” to a compressed air system, they can be found with the Ultrasonic Leak Detector. 

Pressure drop is more of a wide range issue.  It is based on restrictions, obstructions, and piping surface.  Out of these, restrictions are the most common types of pressure drops. The air flow is forced into small areas, causing high velocities.  The high velocity creates turbulent flow which increases the losses in air pressure.  Flow within the pipe is directly related to the velocity times the square of the diameter.  So, if you cut the I.D. of the pipe by one-half, the flow rating will be reduced by 25% of the original rating.  Restriction type of pressure drop can be found in different forms like small diameter pipes or tubing; restrictive fittings like quick disconnects and needle valves, and undersized filters, regulators and valves.

As a rule, air velocities will determine the correct pipe size for the distribution system.  It is beneficial to oversize the pipe to accommodate for any expansions in the future.  For header pipes, the velocities should not be more than 20 feet/sec (6 meter/sec).  For the distribution lines, the velocities should not exceed 30 feet/sec (9 meter/sec).  In following these simple rules, the distribution system can effectively supply the necessary compressed air from the supply side to the demand side.

To have a properly designed distribution system, the pressure drop should be less than 10% from the reservoir tank to the point-of-use.  By following the tips above, you can have the supply side, demand side, and distribution system working at peak efficiency.  If you would like to reduce waste even more, EXAIR offers a variety of efficient, safe, and effective compressed air products to fit within the demand side.  This will include the EXAIR Super Air Knives, Super Air Nozzles, and Safety Air Guns.  This would be the pneumatic equivalent of changing those incandescent light bulbs into LED light bulbs.  If you wish to go further in optimizing your system, an Application Engineer at EXAIR will be happy to help you. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Photo:  Lightbulb by qimono.  Pixabay Licence

Pressure Drop Chart by Compressed Air Challenge Organization.