Piping and Instrumentation diagrams (P&ID)

When it comes to drawings and diagrams to map out a process system, the piping and instrumentation diagrams (P&ID) are a great way to situate and find components.  They use different symbols to represent the type of products, the layout in the system, installation, and process flow.  These standard symbols are created by ANSI or ISO.  They are used in electrical, hydraulic, and pneumatic processes.  Since EXAIR has been manufacturing Intelligent Compressed Air Products since 1983, I will cover some pneumatic symbols and the process flow in this blog.

A colleague, Russ Bowman, wrote an article about “Knowing Your Symbols Is Key To Understanding Your Drawings”.  As a reference, air compressors are the start of your pneumatic system, and there are different types as represented by the symbols below.

The one on the left can be used for any air compressor. The others denote specific types of air compressor (from left:) Centrifugal, Diaphragm, Piston, Rotary, and Screw.

Air compressors are considered the fourth utility in industries because they use so much electricity; and they are inefficient.  So, you need to use the compressed air as efficiently as possible.  As a typical pneumatic system, the air compressors, receiver tanks and compressed air dryers would be on the supply side.  The distribution system, or piping, connects the supply side to the demand side.  This symbol is represented by a simple line.  The demand side will have many different types of pneumatic devices.  Since there are so many, ANSI or ISO has created some common types of equipment.  But if there isn’t a symbol created to represent that part, the idea is to draw a basic shape and mark it.

From top left, and then down: Automatic Drain Filter Separator, Pressure Regulator, and Super Air Knife

As an example, if I were to do a P&ID diagram of the EXAIR Super Air Knife Kit; it would look like the above diagram.  The kit will include the Super Air Knife with an Automatic Drain Filter Separator and a Pressure Regulator.  The Filter Separator is a diamond shape and since it has an Automatic Drain, a triangle is placed at the bottom.  Filter Separators are used to clean the compressed air and keep the Super Air Knife clean.  The Automatic Drain will discard water and oil from the filter bowl when it accumulates over a float.  The next item is the pressure regulator which is represented by a rectangle with an adjustment knob to “dial in” the desired blowing force.  And at the end, we drew a rectangle, which does represent a Super Air Knife, as marked.

Using the P&ID diagram for the process flow is also important.  You noticed that the Filter Separator will come before the Pressure Regulator.  This is significant when installing this system.  Remember the statement above about “using your compressed air as efficiently as possible”?  Inefficiencies come from two basic areas; pressure drop and overusing your compressed air.  Pressure drop is based on velocity.  The lower the velocity, the lower the pressure drop.  If the Filter Separator is placed after the Pressure Regulator, the lower pressure will increase the velocity.  Since air expands at lower pressure, the volume of air will increase.  And since the area of the compressed air pipe is the same, the velocity will have to increase.   For the second part with overusing compressed air, the Pressure Regulator will help.  You want to use the lowest amount of air pressure as possible for the Super Air Knife to “do the job”.  The lower air pressure will use less compressed air in your operation.

EXAIR products are engineered to be safe, efficient, and effective in your compressed air system.  If you need help to place them in your P&ID diagrams, an Application Engineer can help you.  It is important to have the pneumatic devices in the proper place, and if you want to efficiently use your compressed air, you can use EXAIR products for your blow-off devices.

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

Understanding Compressed Air Supply Piping

An important component of your compressed air system is the supply piping. The piping will be the middle man that connects your entire facility to the compressor. Before installing pipe, it is important to consider how the compressed air will be consumed at the point of use.  You’ll also need to consider the types of fittings you’ll use, the size of the distribution piping, and whether you plan to add additional equipment in the next few years. If so, it is important that the system is designed to accommodate any potential expansion. This also helps to compensate for potential scale build-up (depending on the material of construction) that will restrict airflow through the pipe.

Air Compressor
Air Compressor and Storage Tanks

The first thing you’ll need to do is determine your air compressor’s maximum CFM and the necessary operating pressure for your point of use products. Keep in mind, operating at a lower pressure can dramatically reduce overall operating costs. Depending on a variety of factors (elevation, temperature, relative humidity) this can be different than what is listed on directly on the compressor. (For a discussion of how this impacts the capacity of your compressor, check out one of our previous blogs – Intelligent Compressed Air: SCFM, ACFM, ICFM, CFM – What do these terms mean?)

Once you’ve determined your compressor’s maximum CFM, draw a schematic of the necessary piping and list out the length of each straight pipe run. Determine the total length of pipe needed for the system. Using a graph or chart, such as this one from Engineering Toolbox. Locate your compressor’s capacity on the y-axis and the required operating pressure along the x-axis. The point at which these values meet will be the recommended MINIMUM pipe size. If you plan on future expansion, now is a good time to move up to the next pipe size to avoid any potential headache.

After determining the appropriate pipe size, you’ll need to consider how everything will begin to fit together. According to the Best Practices for Compressed Air Systems from the Compressed Air Challenge, the air should enter the compressed air header at a 45° angle, in the direction of flow and always through wide-radius elbows. A sharp angle anywhere in the piping system will result in an unnecessary pressure drop. When the air must make a sharp turn, it is forced to slow down. This causes turbulence within the pipe as the air slams into the insides of the pipe and wastes energy. A 90° bend can cause as much as 3-5 psi of pressure loss. Replacing 90° bends with 45° bends instead eliminates unnecessary pressure loss across the system.

Pressure drop through the pipe is caused by the friction of the air mass making contact with the inside walls of the pipe. This is a function of the volume of flow through the pipe. Larger diameter pipes will result in a lower pressure drop, and vice versa for smaller diameter pipes. The chart below from the Compressed Air and Gas Institute Handbook provides the pressure drop that can be expected at varying CFM for 2”, 3”, and 4” ID pipe.

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Air Pressure Drop

To discuss your application and how an EXAIR Intelligent Compressed Air Product can help your process, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer
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Images Courtesy of  the Compressed Air Challenge and thomasjackson1345 Creative Commons.