Opportunities for enhancing compressed air system performance

How to plan, install and operate a shop compressed air system


The compressor draws in ambient air from its environment, which by nature contains water. For example: On a 75 degrees F day with 75 percent relative humidity, a 10 hp compressor can introduce up to 7.5 gallons of water into a compressed air system. At 90 degrees F with 90 percent relative humidity, that same compressor will introduce 15 gallons of water in the compressed air system per day.

A reliable automatic drain will remove that liquid so the tank stores air, not water.

LEAKS

Find and fix leaks – Leaks are very, very common. Numerous compressed air industry studies confirm that as much as 35 percent of all compressed air produced is lost through leaks.

Leaks waste energy and steal air from tools that need it. A 1/16” leak loses 7 to 8 CFM at 120 psig. At 150 psig, it loses 9 to 10 CFM. That’s half the air from a 5 hp compressor.

Hoses, pipe joints, valves and fittings are hot spots for leaks. If you can hear or feel a leak, the savings from fixing it will pay back the repair cost almost immediately.

There are other techniques for finding the leaks you cannot easily hear or feel, but start with the obvious ones. (For a free white paper on leak detection go to www.kaeser.com/whitepapers.)

PRESSURE DROP AND PIPING

Restrictions in airflow create air turbulence/friction that reduce system pressure. The major causes are: piping that is too small in diameter, rough pipe interior, too many bends and turns in the distribution system, changes in system diameter and un-serviced filters.

There will always be some pressure drop, but it can be greatly reduced with proper system design and maintenance.

Correct the true causes of the pressure drop – Do not try to overcome pressure drop with more horsepower. Trying to stuff more air flow won’t overcome the pressure drop. It will just use more electricity.

Be sure to account for the total pressure drop when selecting the compressor’s operating pressure. An important rule of thumb is that every 2 psi increase in pressure increases energy consumption 1 percent. Therefore, increasing system pressure to overcome pressure drop will consume more energy, increase the amount of air lost through leaks and shorten motor life.

Consider a larger pipe diameter – Pressure drop changes exponentially with pipe diameter. Bigger is better. Bumping up just one pipe size makes a big difference in pressure drop.

For example: The pressure drop of 40 CFM from a 10 hp compressor through 500’ of straight 3/4” smooth pipe would be about 8 psi. If another 10 hp compressor was added, the total flow would be about 80 CFM and the pressure drop would increase to 32 psi.

An increase to 1” diameter pipe would change these numbers to 2 psi and 9 psi, respectively.

The longer the pipe run, the more the pressure drop, but pressure drop increases only proportionally with length.

Other piping recommendations – Compressed air piping material and condition impact performance, pressure drop, energy costs and air quality. Here are some tips for system design:

  • Plan for future growth and install the largest pipe diameter feasible.
  • Minimize the use of pipe “T”s and right angles.
  • Install a flexible hose between the compressor or tank and the piping to eliminate stress on pipe connections caused by compressor vibration.
  • Provide adequate bracing/support when hanging pipe from ceilings or walls.
  • Use only full flow ball valves to minimize pressure drop.
  • Loop distribution to balance pressure and flows at all points of use.
  • Connect point of use pipe drops to the top of the header to reduce moisture carry-over.
  • Install drip legs at each point of use to capture residual moisture.

AIR QUALITY

Compressed air quality is a common issue, especially in summertime and year-round in humid climates. You know you have a problem if oily water is coming out the end of airlines into your tools, tires and spray finishes.

Contaminants increase tool wear and reduce product quality, so it pays to get them out.

Moisture is present in the air – Every 20 degrees F increase approximately doubles the air’s ability to hold moisture. The higher the operating temperature of the compressor, the harder it is to get the moisture to cool and condense out.

Refrigerated dryers are economical and effective in cooling moisture vapor so it can be removed. But dryers are only part of the solution. Almost all the other system components play important roles in moisture and contaminant removal before the air gets to the dryer.

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