There are all kinds of engineering drawings, used for all kinds of purposes:
Pipe fitters and millwrights use Plan & Elevation drawings to make sure fluid system flanges, elbows, tees, etc., line up with each other, and don’t run into anything.
Exploded view drawings help maintenance folks identify parts, and, when they need replaced, make sure the new ones go in the same way the old ones came out.
Fabrication and machining drawings (usually to scale) are used to ensure the part being made is the right size & shape, that mounting holes are in the right place, and that critical surfaces are as flat & smooth as they need to be.
Then there’s the Piping & Instrumentation Diagram (P&ID)…it depicts an overall view of a system, showing the flow (usually fluid or electricity) through that system’s components, giving the viewer an understanding of the operation, and expected results from said operation. It should not be confused with its simpler cousin, the flow chart that is so dreaded by OTE-types (“Other Than Engineer”…you know who you are,) of which these are my favorite examples:
The big difference between a flow chart and a P&ID is the symbols. In fact, you can find ISO & ANSI standard symbols for many components you’ll find in fluid & electrical P&ID’s. Some examples of symbols you might find in a compressed air system are:
Air preparation & handling:
Instrumentation and control:
Occasionally, we’re asked if there are standard ANSI or ISO symbols for any of our engineered Intelligent Compressed Air Products…and there aren’t. Perhaps one day they might make the cut, but for now, their standard convention is to choose a shape (user preference…you’re the one it’s gotta make sense to) and call it out by name. It might look something like this:
Oh, and if you’ve ever got any questions about your compressed air system that you think looking at a drawing together could help us solve, you can send that drawing to us at email@example.com, and one of us will be happy to help.
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Compressed air is used to operate pneumatic systems in a facility, and it can be segregated into three sections; 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 are the collection of end-use devices that will use the 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, I like to compare to the compressed air system, is an electrical system. The air compressor will be considered the voltage source, and the pneumatic devices will be marked as light bulbs. To connect the light bulbs to the voltage source, electrical wires are needed. The distribution system will represent the electrical wires. If the wire gauge is too small to supply the light bulbs, the wire will heat up and the voltage will drop. This heat is given off as wasted energy, and the light bulbs will 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. 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 reference to my analogy, it will keep the lights on.
To optimize the compressed air system, we need to reduce the amount of wasted energy; pressure drop. Pressure drop is based on restrictions, obstructions, and piping surface. If we evaluate each one, a properly designed distribution system can limit the unnecessary problems that can rob the “power” from your pneumatic equipment.
Restriction: This is the most common type of pressure drop. 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 to 25% of the original rating; or the velocity will increase by four times. Restriction can come in different forms like small diameter pipes or tubing; restrictive fittings like quick disconnects and needle valves, and undersized filters and regulators.
Obstruction: This is generally caused by the type of fittings that are used. To help reduce additional pressure drops use sweeping elbows and 45-degree fittings instead of 90 deg. elbows. Another option is to use full flow ball valves and butterfly valves instead of seated valves and needle valves. If a blocking valve or cap is used for future expansion, try and extend the pipe an additional 10 times the diameter of the pipe to help remove any turbulence caused from air flow disruptions. Removing sharp turns and abrupt stops will keep the velocity in a more laminar state.
Roughness: With long runs of pipe, the piping surface can affect the compressed air stream. As an example, carbon steel piping has a relative rough texture. But, over time, the surface will start to rust creating even a rougher surface. This roughness will restrain the flow, creating the pressure to drop. Aluminum and stainless steel tubing have much smoother surfaces and are not as susceptible to pressure drops caused by roughness or corrosion.
As a rule, air velocities will determine the correct pipe size. 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/min (6 meter/min). For the distribution lines, the velocities should not exceed 30 feet/min (9 meter/min). 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 reach that goal and 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 would be the pneumatic equivalent of changing those light bulbs at the point-of-use into LEDs.
What is Air? Air is an invisible gas that supports life on earth. Dry air is made from a mixture of 78% Nitrogen, 21% Oxygen, and 1% of remaining gases like carbon dioxide and other inert gases. Ambient air contains an average of 1% water vapor, and it has a density of 0.0749 Lbs./cubic foot (1.22 Kg/cubic meter) at standard conditions. Air that surrounds us does not have a smell, color, or taste, but it is considered a fluid as it follows the rules of fluid dynamics. But unlike liquids, gases like air are compressible. Once we discovered the potential of compressing the surrounding air, we were able to advance many technologies.
Guess when the earliest air compressor was used? Believe it or not, it was when we started to breathe air. Our diaphragms are like compressors. It pulls and pushes the air in and out of our lungs. We can generate up to 1.2 PSI (80 mbar) of air pressure. During the iron age, hotter fires were required for smelting. Around 1500 B.C., a new type of air compressor was created, called a bellows. You probably seen them hanging by the fireplaces. It is a hand-held device with a flexible bag that you squeeze together to compress the air. The high stream of air was able to get higher temperature fires to melt metals.
Then we started to move into the industrial era. Air compressors were used in mining industries to move air into deep caverns and shafts. Then as the manufacturing technologies advanced, the requirements for higher air pressures were needed. The stored energy created by compressing the air allowed us to develop better pneumatic systems for manufacturing, automation, and construction. I do not know what the future holds in compressed air systems, but I am excited to find out.
Since air is a gas, it will follow the basic rules of the ideal gas law;
PV = nRT (Equation 1)
P – Pressure
V – Volume
n – Amount of gas in moles
R – Universal Gas Constant
T – Temperature
If we express the equation in an isothermal process (same temperature), we can see how the volume and pressure are related. The equation for two different states of a gas can be written as follows:
P1 * V1 = P2 * V2 (Equation 2)
P1 – Pressure at initial state 1
V1 – Volume at initial state 1
P2 – Pressure at changed state 2
V2 – Volume at changed state 2
If we solve for P2, we have:
P2 = (P1 * V1)/V2 (Equation 3)
In looking at Equation 3, if the volume, V2, gets smaller, the pressure, P2, gets higher. This is the idea behind how air compressors work. They decrease the volume inside a chamber to increase the pressure of the air. Most industrial compressors will compress the air to about 125 PSI (8.5 bar). A PSI is a pound of force over a square inch. For metric pressure, a bar is a kg of force over a square centimeter. So, at 125 PSI, there will be 125 pounds of force over a 1” X 1” square. This amount of potential energy is very useful to do work for pneumatic equipment. To simplify the system, the air gets compressed, stored as energy, released as work and is ready to be used again in the cycle.
Compressed air is a clean utility that is used in many different applications. It is much safer than electrical or hydraulic systems. Since air is all around us, it is an abundant commodity for air compressors to use. But because of the compressibility factor of air, much energy is required to create enough pressure in a typical system. It takes roughly 1 horsepower (746 watts) of power to compress 4 cubic feet of air (113L) to 125 PSI (8.5 bar) every minute. With almost every manufacturing plant in the world utilizing compressed air in one form or another, the amount of energy used to compress air is extraordinary. So, utilizing compressed air as efficiently as possible is mandatory. Air is free, but making compressed air is expensive
If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Products, you can contact an Application Engineer at EXAIR.
I would like to dive into the realm of filters and regulators. Majority of EXAIR products use compressed air to coat, conserve, cool, convey or clean. So, to keep the product running efficiently, we need to supply them with clean, dry, pressurized air. We offer a line of filter separators, oil removal filters, and regulators that can supply enough pressure and flow to keep the EXAIR products performing for a very long time. If we look at each individual item, we can see how they can play an important part in your compressed air system.
Regulators are used to control the amount of air pressure being supplied to your EXAIR products. This is important if you are trying to control the flow, force, and/or conveyance rate. One issue with regulators is “droop”. Droop is the amount of pressure drop when you flow through a regulator. If you set the pressure of a regulator with no flow, to let’s say 80 psig (5.5 barg). Once you start flowing, you will see the downstream pressure fall. This is dependent on the size of the regulator and the valve inside. This is very important because if you need 80 psig (5.5 barg) downstream of the regulator feeding an EXAIR product and the droop brings it to 30 psig (2 barg), you will not have enough flow for your EXAIR product, losing performance. EXAIR recommends a specific regulator for each of our products. We tested our products with the recommended regulators to make sure that you are able to get the best performance. If you do use another manufacturer’s regulator, make sure you are able to flow the correct amount of air at the pressure you need. Not all ¼” regulators flow the same.
Filter separators are used to remove liquid condensate and contamination from the compressed air stream. They have a 5 micron filter and work very well if you get a slug of water or oil into your compressed air system. They use mechanical separation to remove the large particles of dirt and water from the air stream. Most facilities have some type of compressed air dryer in their system. This will dry the compressed air. But, if a system failure occurs, then water, oil, and dirt are pushed into the compressed air lines and perhaps into your EXAIR products. Even if you have good quality air, it is important to keep your products protected. An ounce of prevention ….
The oil removal filters are used to keep the compressed air even cleaner yet. They work great at removing very small particles of dirt and oil. Without an oil removal filter, dirt particles and oil particles can collect in “dead” zones within the compressed air lines. Over time, a tacky glob forms. As it grows, it can break off and get into the air stream affecting pneumatic devices. The oil removal filter will be able to help eliminate the long term effects in your compressed air system. As a note, oil removal filters are not great for bulk separation. If you have a system with lots of water, you will need a filter separator in front of the oil removal filter to optimize the filtration. With the oil removal filters, the media is a barrier to collect the small particles of dirt and oil. If a slug of water or oil tries to go through, it will block a portion of the element off until it is forced through. This will increase the velocity and pressure drop of the element. With the high velocity, as the slug makes its way through the media, it can spray, re-entraining the liquid particles.
Now that we went through our pneumatic products, how do we use them together to get the best supply of compressed air? With both types of filters, we always want them to be upstream of the regulator. This is because the velocity is lower at higher pressures. Lower velocities mean smaller pressure drops which is good in filtration. If we can analyze the compressed air systems, I would like to categorize it into a good and premium quality. To supply a good quality of compressed air, you can have the compressed air run through the filter separator then a regulator. To produce the premium quality of compressed air, you can have your compressed air run through the filter separator, the oil removal filter, and then the regulator. With clean quality air, your EXAIR products will provide you with effective, long-lasting performance without maintenance downtime.
What can you do when the pneumatic positioner in your high temperature application is overheating? Call EXAIR!
Or email (and call), as was the case in this application. An end user in an overseas power plant uses a pneumatic positioner in their steam bypass system. A pneumatic positioner can best be correlated to a PWM (Pulse Width Modulated) linear actuator. It will take a supply signal of various forms and provide an output to an actuator or valve, most often to regulate pressure/flow. So, why not just use a pressure regulator? Because a pneumatic positoner can be programmed to respond differently to different inputs, and it can function in real time. Meaning, that when the supply signal reaches a certain threshold the output action can be preset, adding precision to a pneumatically controlled application. And, as application needs change, the adjustments can be automated.
Some pneumatic positioners are pneumatically controlled (the input signal is a compressed air pressure), but most are electronic. The end user in this case was using an electrically controlled unit that was experiencing shutdown due to the high ambient temperatures.
When cooling in an application like this it is important to consider the needs (and restrictions) of the application. To blow ambient air was not an option because of the high ambient temperature, so a Super Air Amplifier, Super Air Knife, or Super Air Nozzle weren’t viable options. And, the pneumatic positioner was exposed to ambient conditions, with no intent to place within an enclosure.
The lack of an enclosure ruled out a Cabinet Cooler, but a Vortex Tube based solution was still possible. When considering the heat load and required cooling capacity, the end user determined that with less than 200 BTU/hr. of cooling, the application should run flawlessly. This customer also expressed they may have fluctuations in there pressure supply, and ambient temperatures which would create the need to provide a larger Btu/Hr Vortex Tube in order toake up for lower pressures and increased temperatures. Our smallest Vortex Tube is capable of producing 550 Btu/Hr and was recommended for a successful application.
If you have an application problem in need of compressed air solutions, call an EXAIR Application Engineer.