Tag: air pressure drop

Pressure Drop vs Differential Pressure

Published on by John BallLeave a comment

I find myself interchanging these terms; pressure drop and differential pressure.  This is very common as both are determined by the change in pressure between two points.  In this blog, I will cover the difference between these two terms in my view.

Pressure drop only occurs when the air is flowing.  The higher the velocity, the higher the pressure drop.  Velocity is created when the pressure changes.  So, the higher pressure will go toward the lower pressure.  But we wish that pressure difference to be as low as possible.  Pressure drops are always a loss, and you cannot regain that energy.  Forms of pressure drop that can be found are small diameter pipes or tubing; restrictive fittings like quick disconnects, and undersized conditioning equipment like after coolers and air dryers.  If a pressure drop is too large, the pneumatic equipment will not have enough power to operate effectively and efficiently.  I have another blog with a video that helps demonstrate this, “Pressure Drop and its Relationship to Compressed Air”. 

Differential pressure can be static or flowing.  It is very similar to pressure drop except that the energy is stored.  The most common device that does this is the pressure regulator.  You can reduce the pressure downstream to the point-of-use.  This type of pressure reduction will save you money, instead of wasting money.  For every 10 PSI reduction in pressure, it will save you 5% in energy.  With blow-off devices, you want to use the least amount of pressure to “do the job”.  Over-driving compressed air pressure is a common and wasteful condition found in facilities.

Here is a graph of a typical compressed air system.  As you can see, the typical pressure drop from the air compressor to the point-of-use.  So, if you can reduce the pressure drop through the system and optimize the differential pressure from the regulator to your point-of-use, you can enhance your compressed air system.

Pressure Drop Chart

In a simple statement, pressure drop loses energy while differential pressure stores energy for later use.  EXAIR offers a variety of efficient, safe, and effective compressed air products to fit within the demand side and which can help to reduce pressure drops within a system.  This will include the EXAIR Super Air Knives, Super Air Nozzles, and Safety Air Guns.  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

Pressure Drop vs Differential Pressure

Published on by John BallLeave a comment

I find myself interchanging these terms; pressure drop and differential pressure.  This is very common as both are determined by the change in pressure between two points.  In this blog, I will cover the difference between these two terms in my view.

Pressure drop only occurs when the air is flowing.  The higher the velocity, the more extreme the pressure drop will be.  Velocity is created when the pressure changes.  So, the higher pressure will go toward the lower pressure.  But we wish for that pressure difference to be as low as possible.  Pressure drop is always a loss, and you cannot regain that energy.  Forms of pressure drop that can be found are like small diameter pipes or tubing; restrictive fittings like quick disconnects, and conditioning equipment like after coolers and air dryers.  If too large of a pressure drop occurs, the pneumatic equipment will not have enough power to operate effectively and efficiently.  I have another blog with a video that helps demonstrate this, “Pressure Drop and its Relationship to Compressed Air”. 

Pressure Regulators “dial in” performance to get the job done without using more air than necessary.

Differential pressure can be static or flowing.  It is very similar to pressure drop except that the energy is stored.  The most common device that does this is the pressure regulator.  You are able to reduce the pressure downstream to the point-of-use.  This type of pressure reduction stores energy, and it will save you money, instead of wasting money.  For every 10 PSI reduction in pressure, it will save you 5% in energy.  With blow-off devices, you want to use the least amount of pressure to “do the job”.  Over-using your compressed air is wasteful.

Here is a graph of a typical compressed air system.  As you can see, the typical pressure drop from the air compressor to the point-of-use.  So, if you can reduce the pressure drop through the system and optimize the differential pressure from the regulator to your point-of-use, you can optimize your system.

Pressure Drop Chart

In a simple statement, a pressure drop loses energy while differential pressure stores energy for later use.  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.  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

Pressure Drop Chart by Compressed Air Challenge Organization.

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

Your Compressed Air Plumbing Could be Causing your Pressure Drop

Published on by Jordan T ShouseLeave 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, and increases 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 particulate, 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.
Back to back Elbows, Tapered fittings, clean outs and ball vales all cause friction in the line resulting in Pressure loss.

Now, there are culprits on the supply side too: after coolers, 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 us a call.

Jordan Shouse
Application Engineer

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