Pressure drops, incorrect plumbing, undersized piping, insufficient flow; if you hear these terms from tech support of your point of use compressed air products or from your maintenance staff when explaining why a process isn’t working then you may be a victim of improper compressed air piping selection. Often time this is due to a continued expansion of an existing system that was designed around a decade old plan. It could also come from a simple misunderstanding of what size of piping is needed and so to save some costs, smaller was used. Nonetheless, if you can understand a small number of variables and what your system is going to be used for, you can ensure the correct piping is used. The variables that you will want to consider when selecting a piping size that will suit your need and give the ability to expand if needed are shown below.
Minimum Operating Pressure Allowed (psig) – Lowest pressure permitted by any demand side point of use product.
System Pressure (psig) – Safe operating pressure that will account for pressure drops.
Flow Rate (SCFM) of demand side (products needing the supplied compressed air)
Total Length of Piping System (feet)
Piping Cost ($)
Installation Cost ($)
Operational Hours ( hr.)
Electical Costs ($/kwh)
Project Life (years) – Is there a planned expansion?
An equation can be used to calculate the diameter of pipe required for a known flow rate and allowable pressure drop. The equation is shown below.
A = (144 x Q x Pa) / (V x 60 x (Pd + Pa) Where: A = Cross-Sectional are of the pipe bore. (sq. in.). Q = Flow rate (cubic ft. / min of free air) Pa = Prevailing atmospheric absolute pressure (psia) Pd = Compressor discharge gauge pressure (psig) V = Design pipe velocity ( ft/sec)
If all of these variables are not known, there are also reference charts which will eliminate the variables needed to total flow rate required for the system, as well as the total length of the piping. The chart shown below was taken from EXAIR’s Knowledge Base.
Once the piping size is selected to meet the needs of the system the future potential of expansion should be taken into account and anticipated for. If no expansion is planned, simply take your length of pipe and start looking at your cost per foot and installation costs. If expansions are planned and known, consider supplying the equipment now and accounting for it if the additional capital expenditure is acceptable at this point.
The benefits to having properly sized compressed air lines for the entire facility and for the long-term expansion goals makes life easier. When production is increased, or when new machinery is added there is not a need to re-engineer the entire system in order to get enough capacity to that last machine. If the main compressed air system is undersized then optimal performance for the facility will never be achieved. By not taking the above variables into consideration or just using what is cheapest is simply setting the system up for failure and inefficiencies. All of these considerations lead to an optimized compressed air system which leads to a sustainable utility.
In case you don’t normally read the EXAIR blog, the general consensus among all the engineers here is that you can never have enough information. To ensure that we pass on as much information as possible to our customers we have added even more to our website. This time, we have given a vast amount of information on our Atomizing Spray Nozzles.
All of the information can be found on the page shown below.
This information will allow you to easier select the appropriate Atomizing Spray Nozzle for the application. Whether it is spraying a liquid coolant onto a drill press to help cool and lubricate the operation or painting parts, the information is there to help better assist you the customer.
Take a look at the new page and if there is anything that you don’t see there, let us know. We may still have it in our files, if not, maybe we can get it for you fast.
EXAIR uses our blog platform to communicate everything from new product announcements to personal interests to safe and efficient use of compressed air. We have recently passed our 5 year anniversary of posting blogs (hard for us to believe) and I thought it appropriate to share a few of the entries which explain some more of the technical aspects of compressed air.
Here is a good blog explaining EXAIR’s 6 steps to optimization, a useful process for improving your compressed air efficiency:
One of the Above 6 steps is to provide secondary storage, a receiver tank, to eliminate pressure drops from high use intermittent applications. This blog entry addresses how to size a receiver tank properly:
Thanks for supporting our blog over the past 5 years, we appreciate it. If you need any support with your sustainability or safety initiatives, or with your compressed air applications please contact us.
Most facility’s compressed air systems have evolved over time. A spur added here a spur added there. Eventually pressure drop issues develop. Common practice is to increase the air pressure at the compressor. While it may address the symptom it does not address the problem and is very costly. For every 2 PSI increase in pressure requires 1% more energy.
A properly designed system will be a loop with spurs. This will ensure all air
drops will share the air equally. The header loop should be able to carry all the air the compressor is capable of producing. Best practices suggest the distribution header should be sized to allow an air velocity not to exceed 30 ft/second. The formula to calculate this is:
A = 144 * Q * Pa V *60 x (Pd +Pa)
Pipe Diameter = √ (A*4/3.14)
A = cross sectional area if the pipe bore in square inches or ∏ x diameter squared / 4
Q = Flow rate SCFM
Pa = Prevailing absolute pressure. Sea level is 14.7
Pd = compressor gauge pressure or psig.
V = Design pipe velocity ft/sec
Example: Size a header for 500 SCFM at 100 PSI at an elevation at sea level
A = 144 x 500 x 14.7 / 30 x 60 (100 + 14.7) = 5.13 square inches
Pipe diameter then is square root of (5.13 * 4) / 3.14 = 2.56″
So an 2.56″ internal diameter pipe would be the proper size header.
The same formula can be used to calculate the sizes of the drops. In this case you would use the demand flow rate for Q.