Maybe it’s not the couch

Pressure Problems? Check Your Pipe Size First

By: Michael Camber

When it comes to compressed air piping, there are several options.  Most manufacturers or process industries use black iron, galvanized, copper, aluminum or stainless. These may be threaded, brazed, welded or connected with various proprietary fittings.  Generally, we recommend copper or aluminum as cost effective upgrades to black iron and galvanized.  Lighter weight makes them easier to install, and their smooth inner walls reduce pressure drop.  In some cases, stainless steel piping may be required to withstand water, cleaning agents or other corrosive substances in immediate proximity.

But regardless of pipe material, they all come in a variety of sizes, and a key point to understand is the relationship of pipe diameter to how much flow it can handle.  It’s quite common for users to experience low pressure somewhere in their system. In some cases, this may mean there simply isn’t enough flow to meet demand and it’s time to increase system capacity with another compressor. But in many cases, new compressors are installed and the problem persists.

Pushing too much air though a pipe causes pressure drop.   If your plant has grown over time and added production capacity, chances are it has acquired more compressors too.  But if the piping hasn’t been upgraded, you may be suffering pressure drop caused by internal friction.  You may mitigate the problem by adding storage downstream closer to points of use with large demands, but sometimes up-sizing the air lines is the only effective solution to get reliable pressure.

If you are putting in a new air system, you have the opportunity to plan for growth.  It’s common for operators to allow space for future compressors as they grow, but adding compressors is far less disruptive and expensive than trying to re-pipe later when you find you cannot stuff all the air you need into the original piping.  Better to bump up the pipe a size or two to allow for additional air flow that may be added later when you expand operations.

Below are two scenarios that illustrate the impact of pipe on pressure loss and how planning ahead can help.

Small system example:

You build a shop with two 10 hp units (total flow is approx. 80 cfm at 125 psig).  Using 1″ diameter pipe, you will lose about 7 psi through 500 ft of piping at full flow.  If you bumped it up to 1 ¼ ” that pressure drop would be less than 2 psi.

Two years later, due to business growth, you add another 10 hp.  Now you have a max flow of 120 cfm.  If you built the shop with the 1″ line, you would suffer 20 psi pressure drop.  In the 1 ¼” line, the loss would be only about 4 psi.  If you doubled the flow from 80 to 160 cfm, the pressure drop would be 30 psi in the 1″ line and only 7 psi in the 1 ¼”.   

Larger system example:

You open a plant with two 100 hp compressors (total flow is approx. 900 cfm at 125 psig).  Using 3″ diameter pipe, you will lose about 6 psi through 1000 ft of piping at full flow.  If you bumped it up to 4″ that pressure drop would be less than 2 psi. 

Two years later, due to business growth, you add another 100 hp.  Now you have a max flow of 1350 cfm.  If you built the shop with the 3″ line, you would suffer 15 psi pressure drop.  In the 4″ line, the loss would be only about 2 psi.  If you doubled the flow from 900 to 1800 cfm, the pressure drop would be 30 psi in the 3″ line and only 7 psi in the 4″. 

The calculations above were based on Table 8.15 Loss of Air Pressure Due to Friction in the CAGI Handbook, Sixth Edition. If you are suffering pressure loss, check your pressure/flow combination in this chart before thinking of adding another compressor. If it seems like you have adequate piping, the next step is to find and fix leaks. Try to get leakage under control (less than 10% of demand) before adding compressors. Pressure drop through dryers and filters may compound the problem. There will always be some drop through air treatment components, but keeping up with maintenance will minimize pressure losses.

Another home remedy to overcome pressure drop is adjusting the compressor discharge pressure higher. If this is effective and necessary, by all means do it, but keep in mind that power consumption increases by 1% for every 2 psi increase. The larger the system, the larger the additional power costs from cranking up the pressure. Adding 5-10% to the 300 hp air system above could easily add $10,000-15,000 to your power bill. And in many cases it just won’t help. The pipe may simply be too small for the volume of air going through it.

Harder to calculate —but often more costly— are the scrap, lost production and downtime resulting from equipment getting low or inconsistent pressure. While those numbers vary from business to business, we’ve read the average cost of downtime for manufacturers is $23,000 per hour. Before you dismiss the need to upgrade your air piping, you owe it to yourself to do that math .

P.S. Our website has a handy pressure drop calculator!

Is it me, or is it hot in here?

By: Michael Camber

Later this month we are going to Cast Expo, the trade show for metal castings producers.  In talking to colleagues about foundries and their applications, it is clear that compressed air is as vital in this industry as it is to most manufacturers.  Unfortunately, while they rely on compressed air, the foundry environment is often horrible for air compressors and dryers.

In metal casting, the combination of high heat from molten metal and high loads of pervasive airborne particulate including silica, fly ash, and coke dust will almost certainly increase down time for maintenance and may reduce equipment life.  Filter changes, oil changes and cooler cleaning must all be done more frequently to keep the compressors running within acceptable temperature ranges.  Motors and electrical cabinets don’t do well with heat or particulate either (especially if it’s combustible). Further, high compressor discharge temperatures decrease the effectiveness of dryers downstream, resulting in more moisture in pneumatics. The stakes are high. One of our foundry customers calculates losses from downtime at $22,000 per hour. 

In some cases, the ambient temperature is simply too high for the compressors and dryers to work well, even with aggressive maintenance plans.  It’s not unheard of for compressor rooms in foundries to be 120°F.  For the health and longevity of the compressors, and continuity of operations, it’s best to place the compressed air equipment as far from these conditions as possible.   This is not always practical.  At the very least, it may require longer pipe runs, and if space isn’t available in another part of the plant, a new building may be necessary. 

Modular structure option at a Virginia foundry

Obviously, new construction gets pricey and time consuming.  Building design, permitting and construction, take time and attention.  An option is modular structures vs brick and mortar.  Depending on design, these can be weatherproof and well ventilated to suit the needs of compressors.  In some cases, the enclosures can be fabricated off site and delivered with the compressed air equipment pre-installed.  This saves time and money on installation and doesn’t disrupt operations on site.   It also takes less time to commission, and often doesn’t require construction permits.  We’ve had several customers take this path with great success. 

Whether building a new building, using pre-fabricated enclosures, or re-purposing existing space in the plant, careful attention to proper (temperature controlled) ventilation and dust control will be vital to compressed air system reliability.  Keeping maintenance costs low and extending compressor life will ultimately pay off with reduced downtime.   At $22,000 per hour, it’s worth the investment.

Calculating the Value of Avoided Unplanned Downtime

By Matt McCorkle

In a recent article titled “Calculating the value of avoided unplanned downtime” from Plant Services magazine, Burt Hurlock poses the question “How much have the avoidable catastrophic events of the 21st century cost us, and how much would we have willingly spent to prevent them?”

He goes on to talk about how downtime events that were avoided still have value and sophisticated plant operators know exactly how much value. Understanding that downtime, of any length, has rippling effects on the entire organization is valuable in itself. One small event can cause unproductive labor hours, costly incident investigation, wasted raw materials, product spoilage, etc. and the bigger the event, the higher the risk and higher the cost is.

Knowing that your compressed air system is not only critical to your production but also affects the quality of your products, would you invest to avoid downtime from your compressed air system? We often encounter customers who tell us “If my compressor goes down, the facility stops.” But in the next breath tell us a back-up compressor isn’t worth the investment. Customers are frequently more concerned with purchasing a larger than necessary compressor that accommodates future growth than planning for the present with a redundant solution.

So, what’s the cost of unplanned downtime? Estimates of the average cost vary from $30,000/hr (Industry research by Stratus) to $260,000 (Aberdeen research). At that rate, any investment in back up quickly pays for itself.

Planning your compressed air system to have redundancy with a back-up compressor or using the 50-50-50 approach with three smaller compressors can help eliminate the risk of unplanned downtime in your compressed air supply. Not only will a multi-unit solution eliminate the compressed air system as a downtime risk for your production lines, it will also supply air more efficiently as your compressed air demands vary by shift and production level.

Ask yourself Burt’s initial question about your own company. “How much have the avoidable events of this year (or the past 2 years or 5 years) cost us, and how much would we have willingly spent to prevent them?”

As Burt Hurlock writes in the article, “all avoided unplanned downtime has value.” Knowing that your compressed air system is vital to your plant, realizing the value, and planning to have a back-up air supply will help you avoid downtime from an unplanned event or even downtime for scheduled maintenance. The value of a reliable second compressor may far outweigh the cost of the downtime it prevents.

Burt goes on to say “The single most important ingredient to the just-right balance between investment and risk is information. Companies that know the value of events that don’t happen also understand that reliability is nine-tenths information and only one-tenth perspiration. The opposite is true for companies that don’t know the value of events that don’t happen.”

When you have your next event, how much will you be sweating?

Compressed air ideas from the IMTS show floor

By Michael Camber

We spotted a good article in Plant Services this week by Ron Marshall, an independent consultant on compressed air efficiency.  Ron reported on some compressed air related innovations he saw at the big International Manufacturing Technology Show (IMTS) last fall.

In addition to covering some new controls and motor designs from compressor manufacturers, he noted some other items he saw that can save energy by reducing compressed air demands. 

Some plants divert compressed air into electrical cabinets for cooling effect.  Ron mentions some alternatives that are much more energy efficient. On a related note, he pointed out that food processors or other plants needing frequent wash down sometimes use compressed air to create positive pressure in electrical cabinets to prevent moisture infiltration.  This is effective but potentially wasteful unless the air is regulated to the minimum pressure required. Other items of interest were devices to detect leaks within pneumatic equipment and air saving nozzles for air knives. While we often emphasize methods to optimize the supply of compressed air, reducing demand-side inefficiencies is equally important.  

Check out his article here.  And while you are at it, if you are not familiar with Compressed Air Best Practices, you are missing out on a good source for ideas to improve your operations. 

Your eyes are often bigger than your stomach

A report card on compressed air knowledge: Part 2

By Michael Camber

Missed part 1?

Click here for the results of a recent quiz of automotive service shops about compressed air.

The point least understood among the surveyed compressor users is how to size a system for the shop.  We presented a scenario with five techs, each using 15 cfm tools, and gave five different compressor size (hp) options. Less than 40% picked the most appropriate option, and most incorrect answers were heavily over-sized.  We see this in the field all the time.  Operators routinely overestimate the size of compressor needed.

Depending on the type and design efficiency, most commercial/industrial compressors produce between 3 and 4.5 cfm per horsepower.  The (simplistic) quiz scenario assumed all air users would need air simultaneously.  Using 4 cfm/hp, a 20 hp compressor with 100% duty cycle would supply air to all five users.  As mentioned above, 40% chose this option, but another 40% chose either the 30 or 50 hp options. 

The downsides to oversizing include:

  • spending more up-front for the equipment (compressors, dryers, etc)
  • paying more for parts and service
  • increased wear from over-cycling (starts and stops)
  • reduced energy efficiency (this applies more to rotary type machines than pistons, which mostly operate on start/stop controls)

Now factor in the reality that it is very rare for all techs to be operating air tools at the same time.  So let’s say only three of five people will be using air simultaneously (total of 45 cfm).  A 15 hp compressor would easily handle it.  If only two out of five were using air at the same time, an efficient 7.5 hp with 100% duty cycle might suffice.  Or bump it to 10 hp (40 cfm) and add 100-200 gallons of storage to be safe.  Far more cost effective than buying the 20 hp.

For energy efficiency, it would be better to get two smaller machines than one large one. This also give you back-up, but it does drive up the initial cost.

If you anticipate that you will need more air in the future,  arrange your compressor room/area to allow for additional machines, but only buy what you need in the short term.  The money you save on energy and service will help pay for the upgrade later.

Download our Compressed Air System Installation Guide E-book for more installation tips.