Ask a Question: What causes pressure drop in my compressed air system?
Answer:
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.
How to Minimize Pressure Drop
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.
Additional ways to minimize pressure drop are as follows:
• Properly design the distribution system.
• 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.
• Reduce the distance the air travels through the distribution system.
• 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.
*SOURCE: Improving Compressed Air System Performance: A Sourcebook for Industry is a cooperative effort of the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy
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