Tag: air pressure

Intelligent Compressed Air: Piping and Pressure Drop

Published on by Russ BowmanLeave a comment

Pressure drop is an unavoidable occurrence in compressed air systems. It’s caused by restrictions or obstructions to flow in your system, and that includes…well, everything:

  • No matter how big your header, drops, supply lines, etc. are, pressurized fluid encounters friction with the inside diameter of the conduit through which it flows.
  • Odds are, your header has at least a few elbows, wyes, tees, reducers, etc. Individually, the restrictions from these are usually quite small, but when you look at a system full of them, they can add up.
  • The type of piping your header is made of matters as well. Iron pipe WILL rust, which roughs up the inside wall of the pipe, which adds friction. Copper and aluminum aren’t near as bad, but there’s no such thing as a zero coefficient of friction.
  • Filters force the air flow through very small passages, torturous paths, or directional changes to remove particulates, moisture, and oil/oil vapor.
  • While not a restriction or obstruction, leaks in your system DO let out perfectly good compressed air before it can be used, so they can be included in our discussion.

Before you go off and redesign your air distribution header or remove your filters (DON’T do that!), it’s important to point that, historically, the highest pressure drops occur at or near the points of use:

  • Undersized hoses. The friction mentioned in the first ‘bullet’ above is compounded by increasing length, and decreasing diameter, of your air operated products’ supply lines. If your product’s performance is suffering, look up its rated air consumption and compare that to the flow rating of the length & diameter of the supply line.
  • Quick connect fittings. The push-to-connect types are particularly notorious for this…the air has to flow around the plug that stops flow when it’s disconnected. You can either replace them with threaded fittings, or if you still want the convenience of the quick connect, consider bushing up a size or two. A 3/8 NPT push to connect fitting will flow twice as much as a 1/4 NPT, and a 1/2 NPT will flow over three times as much as a 1/4 NPT fitting. In the EXAIR R&D room, Efficiency Lab, and shop, we actually use 3/4 NPT quick connects for a wide range of testing, demonstration, performance, etc.
  • Leaks. Even if they’re not big enough to cause a pressure drop, they’re still wasting compressed air. And if they ARE causing pressure drops, please stop reading this and go fix them, right now. Yeah; it’s that important.

Now, there are culprits on the supply side too: aftercoolers, dryers, and system filters can all contribute to pressure drops if they’re improperly sized, or, more often, improperly maintained. For troubleshooting, your first and best shot is to have pressure gauges at strategic locations…you can’t manage what you don’t measure. And not managing it can get costly:

  • Let’s say your compressor discharge header pressure is set to 100psig, but an undersized hose is only letting you get 65psig to an air operated product that really needs 80psig. You can increase your header pressure to 115-120psig to “push” more air through that hose, but keep in mind that all your other unregulated loads will get that pressure increase as well: pneumatic cylinders would operate faster, impact drivers will generate more torque, blow off devices will use more air (and get louder), etc.
  • Even if those things weren’t a problem, it’s going to cost you more. For every 2psi increase in your compressor’s discharge pressure, its power consumption increases by 1 percent. So, for the 20psi increase, it’s going to cost you about 10% more to operate that compressor. A larger diameter air hose, on the other hand, is a one time investment that doesn’t affect the rest of your compressed air system.
  • If you haven’t fixed the leaks I mentioned above yet, increasing your supply pressure will increase the leakage flow rate and, especially if the leak’s in a hose or hose fitting, it can tear that opening wider, compounding the leakage flow rate further.

EXAIR Corporation is keen on making sure you get the most out of our products, and your compressed air system. If you’ve got questions, we’ve got knowledge, and a wealth of resources to help…give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Dead Serious About Dead End Pressure and Chip Guarding – OSHA 1910.242(b)

Published on by codybiehleLeave a comment

Compressed air is a very versatile utility that can be used for applications in cooling products to cleaning off workspaces and products. That is where OSHA 1910.242(b) comes into play; this OSHA standard states that compressed air used for cleaning shall not be used except were reduced to less than 30 psi and then only with effective chip guarding and personal protective equipment. This standard is in place because in the event a dead end occurs, the static pressure at the main orifice can potentially force the high pressure air into someone’s bloodstream and cause an air embolism, which if left untreated can impede the flow of blood in the body and lead to a fatality.

Keeping that in mind there are two ways you can go about these cleaning applications and still stay in compliance with the OSHA standard. The first way is to regulate the air pressure in your pipe down to below 30 psig. But for the majority of applications this is not an effective solution as pressure does equate to the amount of force that can be produced from the system. The second solution is to use a nozzle that is engineered in a way the it cannot be dead ended. This means that the nozzle is designed in a way that no matter how hard you try the air coming out of the nozzle will be ejected into the atmosphere and not through skin.

The fins of the Super Air Nozzle allow air to escape and prevent dead-ending the nozzle.

Take EXAIR’s Air Nozzles for example, the fins and orifice placement are designed in a way that allows air escape air into the atmosphere. Once air has exited an orifice into atmospheric conditions the pressure becomes 0 psig but retains the velocity and higher volume from the higher compressed air inlet pressure which produces force.

Model 1210 Soft Grip Safety Air is fitted with an EXAIR Super Air Nozzle. We can also supply it with a Rigid Extension and Chip Shield (right).

In addition, OSHA 1910.242(b) also talks about the use of effective chip guarding, which simply means some method or equipment shall be installed that prevents particles from flying back and hitting the operator. If you look EXAIR’s Safety air guns you will notice that we offer Chip Shields. By simply adding “-CS” to the end of a part number for a Safety Air Gun you can help prevent injuries from flying particles in blow off applications.

If you have any questions or want more information on compressed air safety and OSHA related standards. Give us a call, we have a team of application engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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The Difference Between a Hose and a Tube and Their Effect on Pressure Drop

Published on by johnball2014Leave 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 source 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. In this blog, I will compare the difference between compressed air hoses and compressed air tubes.

The basic difference between a compressed air hose and a compressed air tube is the way the diameter is defined.   A hose is measured by the inner diameter while a tube is measured by the outer diameter. As an example, a 3/8” compressed air hose has an inner diameter of 3/8”. While a 3/8” compressed air tube has an outer diameter that measures 3/8”. Thus, the inner diameter of the tube will be smaller than the hose.

Why do 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.

As an example, we have a 1/2″ black schedule 40 pipe which has an I.D. of 0.622″.  We use this pipe to flow 40 SCFM of compressed air at 100 PSIG through 100 feet.  What would be the pressure drop?  With Equation 1, imperial units, we get a pressure drop of 1.28 * (40 SCFM/60) ^1.85 * 100 feet / ((0.622″)^5 * 100 PSIG) = 6.5 PSID.  Thus, you started with 100 PSIG, and at the end of the pipe, you will only have (100 PSI – 6.5 PSI) = 93.5 PSIG to use.  Sizing pipe is very important when supplying compressed air to your system as pressure drop is a waste of energy.

Let’s revisit the 3/8” hose and 3/8” tube. The 3/8” hose has an inner diameter of 0.375”, and the 3/8” tube has an inner diameter of 0.25”. In keeping the same variables except for the diameter, we can make a pressure drop comparison in Equation 2.

Equation 2:

As you can see, by using a 3/8” tube in the process instead of the 3/8” hose, the pressure drop will be 7.6 times higher.  As an example, if the pressure drop through a 3/8″ hose is 1 PSID, and you decide to switch out to a 3/8″ tube.  The pressure drop will then be 7.6 PSID, and a big loss of pressure.

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 infeed pipe sizes for each air knife at different lengths. (You will have to sign into 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 drop and get the most from your EXAIR products.

With the diameter being such a significant role in creating 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 under performance of your pneumatic products, as well as wasting money within 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

Photo: Manometers by WebLab24_Siti_Web . Pixabay License

Control Air Pressure at the Point of Use with EXAIR’s Pressure Regulators

Published on by Tyler DanielLeave a comment

In any application necessitating the use of compressed air, pressure should be controlled to minimize the air consumption at the point of use. Pressure regulators are available to control the air pressure within the system and throttle the appropriate supply of air to any pneumatic device. As the last of the six steps to optimizing your compressed air system, controlling air at the point of use can often be overlooked. To help you achieve this, EXAIR offers a line of point of use pressure regulators to make sure you’re operating at the optimal pressure for your application.

Pressure regulators utilize a control knob that is turned to either increase/decrease tension on a spring. The spring puts a load on the diaphragm which separates internal air pressure from the ambient pressure. Typically made of a flexible rubber material, these diaphragms react very quickly to changes in the air supply. By either increasing or decreasing the flow of air based on the load on the diaphragm, downstream pressure remains fairly constant.

Regulator Internal

While one advantage of a pressure regulator is certainly maintaining consistent pressure to your compressed air devices, using them to minimize your pressure can result in dramatic savings to your costs of compressed air.

As pressure and flow are directly related, lowering the pressure supplied results in less compressed air usage. EXAIR recommends operating your Intelligent Compressed Air Products at the minimum pressure necessary to achieve a successful application. If you notice a desirable result at a pressure of 60 PSIG, or even less, there’s no need to run full line pressure. In-line point of use pressure regulators are the simplest and most reliable way to allow you to dial down the pressure to any compressed air operated product. For example, a Model 110012 Super Air Knife will consume 42 SCFM when operated at 100 PSIG. When the pressure is reduced to 60 PSIG, this drops to just 27.6 SCFM. That’s a 34% reduction in compressed air usage, just by dialing down the pressure at the point of use!

When selecting a pressure regulator for your application, it’s critical that it is appropriately sized to supply adequate volume to the point of use devices downstream. Doing so, minimizes the risk of experiencing “droop”. Droop is a decrease in outlet pressure from the specified setting due to an increase in flow rate.  Droop occurs when the demand at the point of use exceeds the volume of air that the regulator can supply. By ensuring the pressure regulator is rated to deliver sufficient volume of air, you’ll reduce the chances of experiencing droop. EXAIR offers pressure regulators in kits along with many of our products, we’ve done the hard part for you and made sure they’re properly sized!

If you’re looking for ways to help lessen the demand on your compressor, EXAIR’s team of Application Engineers will be happy to help. Reach out to us via phone, chat, or e-mail and see for yourself just how easy it can be to start saving compressed air!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD