Tag: Regulated pressure

Common Compressed Air Drawing Symbols

Published on by John BallLeave a comment
The symbols on top denote the EXAIR products below (left to right): Flowmeter, Pressure Gauge, and Solenoid Valve

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 types of products, the layout of the system, installation, and process flow.  These standard symbols are created by ANSI or ISO.  They are used in electrical, hydraulic, and pneumatic processes. 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.

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, Oil Removal Filter, 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 the 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 represents a Super Air Knife, as marked.

Using the P&ID diagram for the process flow is important.  You noticed that the Filter Separator would come before the Pressure Regulator.  This is significant when installing this system.  Did you 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.  For the second part about 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.  If you want to efficiently use your compressed air, you can use EXAIR products for your blow-off devices.  We have been doing this for a long time.

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.

How to Size a Receiver Tank and Improve your Compressed Air System

Published on by John BallLeave a comment

Receiver Tank: Model 9500-60

My colleague, Lee Evans, wrote a blog about calculating the size of primary receiver tanks within a compressed air system.  (You can read it here: Receiver Tank Principle and Calculations).  I would like to expand a bit more about secondary receiver tanks.  They can be strategically placed throughout the plant to improve your compressed air system.  The primary receiver tanks help to protect the supply side when demands are high, and the secondary receiver tanks help systems on the demand side to optimize performance.

Circuit Board

I like to compare the pneumatic system to an electrical system.  The receiver tanks are like capacitors.  They store energy produced by an air compressor like a capacitor stores energy from an electrical source.  If you have ever seen an electrical circuit board, you notice many capacitors with different sizes throughout the circuit board (reference photo above).  The reason is to have a ready source of energy to increase efficiency and speed for the ebbs and flows of electrical signals.  The same can be said for the secondary receiver tanks in a pneumatic system.

To tie this to a compressed air system, if you have an area that requires a high volume of compressed air intermittently, a secondary receiver tank would benefit this system.  There are valves, cylinders, actuators, and pneumatic controls which turn on and off.  And in most situations, very quickly.  To maximize speed and efficiency, it is important to have a ready source of air nearby to supply the necessary amount quickly.

For calculating a minimum volume size for your secondary receiver tank, we can use Equation 1 below.  It is the same as sizing a primary receiver tank, but the scalars are slightly different.  The secondary receivers are located to run a certain machine or area.  The supply line to this tank will typically come from a header pipe that supplies the entire facility.  Generally, it is smaller in diameter; so, we have to look at the air supply that it can feed into the tank.  For example, a 1” NPT Schedule 40 Pipe at 100 PSIG can supply a maximum of 150 SCFM of air flow.  This value is used for Cap below.  C is the largest air demand for the machine or targeted area that will be using the tank.  If the C value is less than the Cap value, then a secondary tank is not needed.  If the Cap is below the C value, then we can calculate the smallest volume that would be needed.  The other value is the minimum tank pressure.  In most cases, a regulator is used to set the air pressure for the machine or area.  If the specification is 80 PSIG, then you would use this value as P2.  P1 is the header pressure that will be coming into the secondary tank.  With this collection of information, you can use Equation 1 to calculate the minimum tank volume.  So, any larger volume would fit the requirement as a secondary receiver tank.

Secondary Receiver tank capacity formula (Equation 1)

V = T * (C – Cap) * (Pa) / (P1-P2)

Where:

V – Volume of receiver tank (cubic feet)

T – Time interval (minutes)

C – Air demand for system (cubic feet per minute)

Cap – Supply value of inlet pipe (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Header Pressure (PSIG)

P2 – Regulated Pressure (PSIG)

If you find that your pneumatic devices are lacking in performance because the air pressure seems to drop during operation, you may need to add a secondary receiver to that system.  For any intermittent design, the tank can store that energy like a capacitor to optimize the performance.  EXAIR stocks 60 Gallon tanks, model 9500-60 to add to those specific locations, If you have any questions about using a receiver tank in your application, primary or secondary, you can contact an EXAIR Application Engineer.  We can restore that efficiency and speed back into your application.

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

 

Photo: Circuit Board courtesy from T_Tide under Pixabay License