We were recently helping a manufacturer of automated car washes think about the impact of compressed air on the operation and reliability of the machines they sell. Automated car washes rely heavily on many pneumatic valves and actuators with high cycling rates for components like chemical (soap) applicators, wrap control arms and other mechanical components. The integrity of the lubrication and seals in these devices is absolutely critical to proper mechanical operation and through-put. This is certainly not unique to the car wash business. The same is true for all pneumatics.
As in many small business applications, the most commonly found compressor at car washes is the piston/recip compressor. The auto wash machinery supplier asked us whether their customers would benefit from using rotary screw compressors instead of the tried and true tank-mounted piston/recip compressor that dominates the 5 to 10 hp markets. They were attracted by the low noise and vibration and wanted to know how the common rotary screw compressor, tank and dryer combinations would affect operations.
Let’s take a quick look at the pros and cons of each compressor as they apply to car washes (and other operations with pneumatics).
Piston compressors operate at much higher temperatures than screw compressors. They are often oversized and run at unnecessary high pressure so that they can periodically shut off and cool down to prevent compressor failure. Further, the hotter air holds more moisture that will make its way to your pneumatic devices. Over time this hot, wet compressed air strips away the lubricants in valves, cylinders, and actuators. The resulting accelerated/premature wear of seals causes pneumatic devices to drag and stick. Coils in solenoids burn out trying to actuate stuck or sluggish valves. These failures result in more frequent maintenance, repair and replacement (in the case of “lubed for life” devices). In addition to the higher operating costs, the downtime for these repairs interrupts operations and causes loss of revenue.
Pros: Lower purchase price, minimal preventive maintenance
Cons: Higher temperatures, limited run time, and more moisture in the air
Compared to the commonly used piston style compressor, all-in-one screw compressor packages (i.e. those that include a tank, dryer and liquid drain) deliver air that is much cooler, cleaner, and drier. This greatly prolongs the life of pneumatic devices, reducing downtime and preserving revenue generating uptime. Screw compressors also deliver more flow (cfm) per horsepower. They have thermostatically controlled cooling circuits and can run continuously without overheating. Combined, these two features often enable the user to buy a smaller rotary screw compressor and get all the air they need.
Cons: Higher purchase price, higher maintenance costs
Pros: Lower temperature and better air quality (protecting pneumatic equipment and increasing uptime), reduced maintenance and higher revenue stream (outweighing the higher costs), lower energy consumption, (more savings), and low noise and vibration.
For reference, here are some details for the rotary screw vs piston compressor comparison:
||1 - 7 ppm
||10 ppm - no upper limit
||65 - 75 dB(A)
||4 - 4.5 cfm/hp
||3 - 3.5 cfm/hp
|Internal operating temp:
||170°F - 200°F
||300°F - 400°F
||15°F - 25°F above ambient
||100°F and higher above ambient
And because "those cars never seem to stop coming," here are some additional resources: