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Tuesday, May 5, 2009

Tips to Reduce Compressed Air System Pressure Drops

Ask a Question:

What causes pressure drops in my compressed air system and how can I reduce them?


Pressure drop can become a compressed air system problem that steals production time and money.

What causes pressure drops? Any type of obstruction, restriction, or roughness in the system will cause resistance to air flow and cause pressure drop.

In the distribution system, the highest pressure drops usually are found at the points-of-use, including undersized or leaking hoses, tubes, disconnects, filters, regulators and lubricators (FRLs).

On the supply side of the system, air/lubricant separators, aftercoolers, moisture separators, dryers and filters can be the main items causing significant pressure drops. The maximum pressure drop from the supply side to the points-of-use will occur when the compressed air flow rate and temperature are highest.

Your Compressed Air System components should be selected based upon these conditions and the manufacturer of each component should be requested to supply pressure drop information under these conditions.

When selecting filters, remember that they will get dirty. Dirt loading characteristics are also important selection criteria. Large end users who purchase substantial quantities of components should work with their suppliers to ensure that products meet the desired specifications for differential pressure and other characteristics.

The distribution piping system often is diagnosed as having excess pressure drop because a point-of-use pressure regulator cannot sustain the required downstream pressure. If such a regulator is set at 85 psig and the regulator and/or the upstream filter has a pressure drop of 20 psi, the system upstream of the filter and regulator would have to maintain at least 105 psig. The 20 psi pressure drop may be blamed on the system piping rather than on the components at fault. The correct diagnosis requires pressure measurements at different points in the system to identify the component(s) causing the excess pressure drop. In this case, the filter element should be replaced or the filter regulator size needs to be increased, not the piping.

Tips to Reduce Pressure Drop:

• Properly design the distribution system.

Minimizing pressure drop requires a "systems approach" in design and maintenance of the system.

Air treatment components, such as aftercoolers, moisture separators, dryers, and filters, should be selected with the lowest possible pressure drop at specified maximum operating conditions.

When installed, the recommended maintenance procedures should be followed and documented.

• Reduce the effective distance of the flow for air to travel through the system.

-Just like water in a garden hose --the longer the hose, the less water pressure at the end. It works the same with air.

-The pressure loss between the compressor and the end user tool comes from friction in the pipe. The smaller the pipe, the greater the friction, and the longer the pipe, the greater the friction.

If you have both of these issues in the same may have substantial pressure drops.

Reduce the friction and restrictions.

-Pressure loss is caused by the friction of the air mass flowing on the side walls of the pipe or hose.

The larger the pipe, the more air it will carry in the center, not causing friction loss on the inside walls.

-A smooth inner lining of the pipe or hose will cause less pressure drop.

-A rough inner lining of the pipe or hose will cause more pressure drop. Pipe corrosion can cause friction and pressure loss.

-Couplings, fittings and valves increase the pressure drop.

-Make sure you have the most efficient system layout possible. You may need to relocate some equipment or re-pipe, but if you are suffering from excessive pressure drops, then the benefit may outweigh the cost.

• Reduce the velocity, or flow rate, of air through the system.

-For a given pipe or hose size and length, the pressure loss increases as the volume of air flow increases.

-Reducing and controlling the system pressure downstream of the primary receiver can result in a 10% or more reduction in energy consumption...even though the compressors discharge pressure had not been changed. Reducing your system pressure can help improve system performance, reducing leakage rates, and helping reduce stress on operating equipment. Note that a reduced system operating pressure may require modifications to other components, such as pressure regulators, filters, and the size and location of compressed air storage.

• Be sure to consider the effects of all your compressed air system's components on pressure.

-Operate and maintain air filtering and drying equipment to reduce the effects of moisture, such as pipe corrosion.

-Select aftercoolers, separators, dryers and filters having the lowest possible pressure drop for the rated conditions. It's important to check if manufacturers are including pressure drops in filters, pressure regulators, and hoses in their pressure requirements for end-use equipment, or if those pressure requirements given are for after those components. The typical pressure differential for a filter, pressure regulator, and hose is 7 psid, but it might be higher if the system is poorly maintained or designed.

-Specify pressure regulators, lubricators, hoses, and connections having the best performance characteristics at the lowest pressure differential. These components must be sized based upon the actual rate of flow and not the average rate of flow.

*SOURCES: "Improving Compressed Air System Performance: A Sourcebook for Industry" - a cooperative effort of the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) Best Practices and the Compressed Air Challenge®; "Energy Savings in Compressed Air" by Hank Van Ormer.

Tommy McGuire

McGuire Air Compressors, Inc.

"Real People with Real Air Compressor Experience"

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