For example, the pressure drop of 40 cfm (from a 10-hp compressor) through 500 feet of straight 3/4-inch smooth pipe would be about 8 psi. If the shop added another 10-hp compressor the total flow would be about 80 cfm and the pressure drop would increase to 32 psi! An increase to 1-inch diameter pipe would change these numbers to 2 psi and 9 psi, respectively. Pressure drop increases with the number of turns in the system and with rough interior surfaces.
There are several piping materials available and the choice has a large impact on air quality and flow. Common materials include:
• Black iron
• PVC or other plastics
• Modular aluminum systems
Each of these materials has its advantages and disadvantages. However, experience shows that copper has the best combination of performance, material cost, and installation cost. The modular aluminum systems show promise, but are still relatively new.
Here are a few piping recommendations
• 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.
An important rule of thumb is that every 2-psi increase in pressure increases energy consumption 1 percent. In addition, the higher the system pressure the greater the volume lost through leaks. A 1/16-inch leak loses 7-8 cfm at 120 psig. At 150 psig, it loses 9-10 cfm. A 1/8-inch leak loses 30 cfm at 120 psig and nearly 38 cfm at 150 psig! 38 cfm is more than many 10-hp compressors can produce.
Price and True Cost
A simple yet thorough system analysis goes a long way in building a reliable, cost-effective system. Carefully consider each system component and its impact on the application. Remember — value is more than initial price. Purchasing quality equipment now will save time and money for years to come.
Getting the most for your money when selecting a compressor.
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