Is PVC Pipe Alright to Use with Compressed Air?

A question arises every now and then on whether or not PVC pipe, yes the stuff from your local hardware store that says it is rated for 200 psi, is safe to use as compressed air supply line.   The answer is always the same,  NO! OSHA agrees – see their statement here.

Schedule 40 PVC pipe is not designed nor rated for use with compressed air or other gases.  PVC pipe will explode under pressure, it is impacted significantly by temperature and can be difficult to get airtight.

PVC pipe was originally designed and tested for conveyance of liquids or products that cannot be compressed, rather they can be pressurized.   The largest concern is the failure method of the piping itself.   When being used with a liquid that cannot be compressed, if there is a failure (crack or hole) then the piping will spring a leak and not shatter.   When introducing a compressed gas, such as compressed air, if there is a failure the method ends up being shrapnel.  This YouTube video does a good job of illustrating how the pipe shatters.

While it may seem that it takes a good amount of pressure to cause a failure in the pipe, that is often not the case.  I have chatted with some local shop owners who decided to run PVC as a quick and cheap alternative to get their machines up and running.

They each experienced the same failures at different points in time as well.  The worst one was a section of PVC pipe installed over a workbench failed where an operator would normally be standing. Luckily the failure happened at night when no one was there.  Even though no one got injured this still caused a considerable expense to the company because the compressor ran overnight trying to pressurize a ruptured line.

Temperature will impact the PVC as well. Schedule 40 PVC is generally rated for use between 70°F and 140°F (21°-60°C). Pipes that are installed outside or in non temperature controlled buildings can freeze the pipes and make them brittle.

If you haven’t worked with PVC before or do not let the sealant set, it can be hard to get a good seal, leading to leaks and a weak spot in the system.

The point of this is the cheapest, quick, and easy solutions are more often , the ones that will cost the most in the long run.

If you would like to discuss proper compressed air piping and how to save compressed air on your systems, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

Image courtesy of: Dennis Hill, Creative Commons License

Sanitary Flange Line Vacs for Bulk Conveying

Piping systems have been a hallmark of human civilization for almost as long as people have been living in community with each other. Evidence of complex earthen pipe systems, with flanged fittings & asphalt sealants, date to 2700 BC. These were used for crop irrigation, potable water distribution, and wastewater removal in ancient civilizations from the Mediterranean to the Far East.

Over the centuries, new ways to use pipe led to new ways to make pipe.  Scientists and engineers figured out ways to make pipe stronger, lighter, cheaper, and in a variety of materials.  One of the more recent milestones is the development of sanitary piping and fittings.  The stringent cleanliness controls in certain industries (food and pharmaceutical, I’m looking at you) require highly corrosion resistant materials of construction.  The inside & outside surfaces of the pipe have to be finely finished so that they can be thoroughly and positively cleaned, with no crevices, “nooks & crannies,” etc., for material to gather or cling.  And since regular cleaning & sterilization is performed, the fittings must be able to be made & unmade in a manner that still provides for positive sealing when the system is restored to operation.

EXAIR Line Vac Air Operated Conveyors have always been well suited for applications like this.  With their open, unobstructed throats and smooth bores, they’re intuitively easy to clean, by design.  And we’ve made them, for years, in Type 316 Stainless Steel – the preferred material of construction for many food and pharmaceutical applications.  Many users in these industries were able to install them in sanitary piping systems by welding the flanges on our Stainless Steel Line Vacs, or by installing adapters on our Threaded Stainless Steel Line Vacs.

In the spring of 2017, EXAIR released the Sanitary Flange Line Vac with those same users in mind – eliminating the need to weld or thread flanges onto existing products.  They feature the same conveyance power as our Stainless Steel Line Vacs, and can even be modified to meet Heavy Duty Line Vac performance, if needed.  There are four sizes: 1-1/2″, 2″, 2-1/2″, and 3″…which covers the most popular size range of sanitary pipe systems.

While the sanitary piping systems are certainly most often found in those cleanliness-critical food & pharma type applications, other users incorporate them because of the smooth, continuous bore of the pipe and fittings, as opposed to a threaded pipe system, where the OD of the pipe threads into the ID of the fittings, causing a “step” in the throughput.  Because sanitary fittings mate via face-to-face flange seals, this eliminates that “step” which can make for a catch-point for certain items.  It’s for this very reason that a popular ammunition manufacturer uses sanitary pipe systems to convey shell casings…because they tumble with such turbulence in the air flow, they are especially prone to hanging up on any kind of catch-point.  So, they use sanitary piping & fittings, long radius elbows, and EXAIR Model 161150-316 1-1/2″ Sanitary Flange Line Vacs.

Air conveying of certain items, like these ammo shell casings, can be prone to clogging or jamming in systems where pipe, hose, and/or fittings are inserted into each other, creating catch-points.

EXAIR has a wide selection of engineered compressed air products that are “textbook” solutions for certain applications, but also make perfect sense for use in places you might not have thought of.  If you have a bulk material conveyance operation you’d like to discuss, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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Shells photo courtesy of hydropeek  Creative Commons License

Troubleshooting Vortex Tube Performance

image-2
This Vortex Tube was not operating properly when initially connected to compressed air

One of the fun parts of Application Engineering at EXAIR is explaining the operation of Vortex Tubes to our customers.  Sometimes they’re described as a “reverse tornado” inside of a tube, spinning a pressurized airstream and converting it into a hot and cold flow.  Other times we describe it through the generation of two vortices with differing diameters, and the difference in diameters results in one vortex shedding energy in the form of heat.

But, no matter the way we explain their operation, we always stress the importance of proper compressed air plumbing.  If the compressed air piping/hoses/connections are not properly sized, performance problems can arise.  (This is true for any compressed air driven device.)

This fundamental came to light when working with one of our customers recently.  They were using a medium sized Vortex Tube to provide spot cooling in an enclosed space, but were not seeing the flow and temperature drop they knew to be possible with an EXAIR Vortex Tube.  And, after looking at installation photos of the application, the root cause was quickly spotted.

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The red arrow in the bottom right corner of this image shows the beginnings of a reduction in compressed air supply.

I noticed what looked to be a very small hose connected to the inlet of the Vortex Tube in the image above.

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In this additional image, the small compressed air line is in full view. This was the root cause for performance problems in this application.

After further inspection of another photo, the small diameter tube was in full view.  This small hose serves as a restriction to compressed air flow, which in turn limits both flow and operating pressure of the downstream devices.  What that meant for this application, was poor performance from the Vortex Tube, all stemming from this reduction in piping size.

When looking to find the root cause of a performance issue with a compressed air driven unit, things aren’t always as easy as they were with this application.  A visual inspection is always a good idea, but if everything looks correct, here is a list of troubleshooting steps to consider:

  1. Check for quick-disconnects in the plumbing system.  Quick-disconnects are great from an operator’s perspective, but they can wreak havoc on compressed air flows due to small inside diameters and air volume restriction.
  2. Determine the operating pressure at the device.  This is imperative.  In order to make proper decisions to correct the performance concern, good information is required.  Knowing what is happening at the device is crucial for proper understanding.  There may be 100 PSIG at the main compressed air line, but only 60 PSIG at the device due to plumbing problems. A pressure gauge at the inlet of the compressed air product can provide this information.
  3. Check that the compressed air system has enough volume to properly supply the device.  A compressed air driven unit without the correct volume of compressed air is just as bad as having a lack of pressure.
  4. Check for leaks.  The US Department of Energy estimates that 20-30% of compressor output in industrial facilities is lost as leaks.  If your system and devices aren’t operating as they’re supposed to, check for leaks.  They may be contributing to the poor performance.  (Don’t know where your leaks are coming from?  Use our Ultrasonic Leak Detector!)

Fortunately for this customer, after improving the size of this tubing performance was on par with our published specifications and this customer was back in operation.  If you have a question about how to improve the utilization of the compressed air devices in your application, contact an EXAIR Application Engineer.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Consider these Variables When Choosing Compressed Air Pipe Size

Here on the EXAIR blog we discuss pressure drops, correct plumbing, pipe sizing, and friction losses within your piping system from time to time.   We will generally even give recommendations on what size piping to use.  These are 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.

The variables to know for a new piping run are as follows.

  • Flow Rate (SCFM) of demand side (products needing the supplied compressed air)
  • System Pressure (psig) – Safe operating pressure that will account for pressure drops.
  • Minimum Operating Pressure Allowed (psig) – Lowest pressure permitted by any demand side point of use product.
  • 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.

Piping
Airflow Through 1/4″ Shed. 40 Pipe

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.

Brian Farno
Application Engineer Manager
BrianFarno@EXAIR.com
@EXAIR_BF