Recently a paint and body shop with two 7.5 hp screw compressors purchased another one with the same capacity. They’d added a blast cabinet and said the system could not keep up. Blast cabinets can certainly be air hogs, so depending on the nozzle size and amount of use, it’s not unreasonable to need more air if you add one to your shop. But…
During the visit to install the new unit, our service technician performed some routine maintenance that had been deferred for well over two years. He immediately noticed that the fluid/lubricant level was less than 25% of what it should be and looked terrible:
At first the tech was surprised that the unit had not overheated. The mystery was solved when he changed the inlet filter and separator cartridge:
They were so clogged that the compressor could not take in enough air to compress. Remember Charles’ Law from high school science class, which taught us that temperature increases with pressure. Compressors generate heat when the energy from the motor is transferred to the compression chamber. Squeezing the air excites air molecules, and as they bump into each other they give off heat. What happens if the compressor is starved for air due to clogged filters? Well, not much compression and not much heat.
This sheds light on an odd statement the customer made to the sales rep some weeks after the installation. He happily reported that since then the shop runs very well. He has plenty of air and the older units don’t seem to come on much at all. So it is quite possible that the existing system was fully capable of supplying all the air he needed even with the blast cabinet. Had the existing units been periodically inspected and maintained, he may not have needed to spend the money on a new compressor, installation, and the additional PM that new unit will require going forward.
Before you presume to blame the sales rep, keep in mind they were not fully aware of the state of the equipment, and the addition of a blast cabinet was a very plausible reason for needing more volume. Still, we can turn this hindsight into foresight.
Lesson learned: before you invest in additional compressors, check to see that the existing compressors are running well and making the air they should be. This applies to any size system.Tweet
A reliable supply of clean, dry compressed air at stable pressure is vital in collision repair. Understanding air pressure, flow and quality requirements will help you extend tool life and get the best possible results in the paint booth to eliminate costly re-work caused by contaminants in the compressed air supply.
Watch the webinar below for best practices for compressed air systems in body shops. If you’re attending SEMA 2019, stop by one of the Kaeser booths to discuss how you can decrease downtime and comebacks…and increase productivity and profit.
Key design factors for evaluating a compressed air system
Common types of contaminants and how to remove them
Air treatment components to ensure clean, dry air for paint and body work
Types of dryers and tips on selecting the right one
With nearly 7,000 existing craft breweries in the US and another 3,000-plus in planning (according to the Brewers Association), the craft beer industry is a fast-growing market. As with other food and beverage industries, compressed air is often vital to production. From smaller craft breweries to large international companies with multiple facilities, each system needs compressed air. The questions are how much and how do their needs differ?
By: Michael Camber, Jeff Owen (Sales Manager for Kaeser USA’s Atlanta branch), and Frank Remsik (System Specialist)
We are in the business of selling rotary screw compressors, and we sell quite a few to users that have outgrown their two-stage reciprocating/piston compressors in the 5 to 20 hp range. Sometimes demand or duty cycle has increased beyond the practical range of their piston compressors. Or they need higher air quality. Sometimes noise and vibration are the issue. But there are many cases where a reciprocating compressor is still a very good, economical fit for the shop, but service issues lead them to think they need a different solution.
Heat is often the enemy
Most small shop recips are not designed to handle 100% duty cycle. In other words, they cannot run flat out for long lengths of time without sustaining heat-related wear or damage. Generally, these small two-stage units operate at relatively high temperatures (275-350°F), so they need to stop and cool down periodically. (This is why they are typically set at 145-175 psig, even though most tools only need 90 psig.) Duty cycles vary — we’ve seen 50% to 80% –depending on the design and quality of construction.
There are a number of heat-related problems, but first let’s talk about what can cause them.
First, the compressor’s environment plays a critical role in its reliability. If the room is too hot, or doesn’t get enough ventilation it will run hotter than designed. To reduce noise, many recips are installed in out of the way locations (e.g. utility closets). Ventilation is often poor, creating more heat and higher discharge temperature.
Second, excessive run time can result in heat-related problems. There are several reasons for excessive run time, and a system can suffer from any or all of them:
The compressor is undersized for the productive demand.
More users or larger tools have been added to the demand.
Leaks have developed (leaks in fittings, hoses and tools are just another type of air user—even if completely unproductive).
Lack of storage in the tank due to water. The air leaving the compressor pump is hot and contains moisture in vapor state. In the tank, the air cools and moisture condenses into liquid. Condensate can build up quickly, especially in warmer, humid climates (gallons per day). If the tank is not routinely drained, it will fill with water leaving less room for air. Less air storage => more run time => more heat =>more problems.
Potential heat-related issues
Below are some of the mechanical issues caused by overheating. Generally, these can be repaired economically.
Piston rings no longer seal properly against cylinder walls, thus losing compression. When this happens the pump may have to run longer (and even hotter) to meet demand. Lubricating oil breaks down faster and gets past the rings more easily, requiring more make-up oil to prevent further mechanical issues (and degrading air quality).
Failed intake / exhaust valves
Oil carry-over builds up and may prevent valves from properly seating, creating blow-by through valves. This can cause the intercooler safety relief to release, and also cause the voltage supply breaker / fuses to trip due to stalling out the pump. Over time this can burn out the drive motor.
failed check valves
Recips tanks have check valves to make sure they don’t start under load. Over time the elevated temperatures along with oil carry-over can distort the nylon piston in the valve, so the piston can’t seal properly. When this happens, back-pressure from the tank will create head pressure on the pump. When the compressor tries to start, the extra amps drawn by the motor can trip breakers and burn the motors out. If you have issues with belts breaking prematurely, it could be from a failed check valve on the tank. If the compressor pump is trying to start against head pressure, the crankshaft may not move even though the motor is. Motor goes, pump won’t -> belts slip/wear/break.
Motor burn out
Motors generate heat in normal operation but will cool themselves adequately unless they are in too hot an environment or are energized and try to turn something that doesn’t want to be turned, such as a pump with head pressure (see above) or one that is not properly lubricated. Over time, the insulation on motor windings will degrade and the motor will need to be rewound or replaced.
By design, reciprocating compressors vibrate. Vibration affect many things. Vibration can loosen piping connections, as well as any threaded nut or bolt. It can loosen up electrical connections and create electrical drop-out, sparking, tripping out breakers and blowing fuses. Pressure switches can also fail due to excessive vibration. Vibration can create cracks in welds and joints at the tank feet, platform and saddles. Excessive vibration also increases noise levels, loosens safety guards, and can even break up a concrete floor.
Replace missing or cracked vibration pads. While you are at it, if the discharge piping from the tank is hard pipe, swap it out for flexible steel braided hose. Same goes for electrical supply from the wall disconnect to the starters. Make sure the belt guard is secure. A missing or loose belt guard is not just a safety issue but is an OSHA violation.
Noise can often be abated with well-placed, insulated stud walls. The key is not to restrict airflow. If you are contemplating constructing a separate room to isolate a hot, noisy compressor, it is worth doing the math to see if a rotary compressor makes sense. The quieter rotary unit may cost less that permitted construction and almost certainly take less time to install. This assumes you have a good place with good ventilation and access, and that the unit will be run enough to gain some of the energy advantage.
A note about tanks
As explained above, storage is vital to the longevity of the compressor. It’s also important for meeting demand and system performance. Tanks don’t need much maintenance but you want to keep them dry. Not just for the storage, but to minimize rust. Over time, rust will build up in the tank and plug up the drain port. This makes the case for a quality automatic condensate drain that won’t get gunked up by the oil-water-rust mixture.
An ounce of prevention
The piston style compressor is simple and requires relatively little service, but it cannot be ignored. Here are some tips, whether you are installing new or want to keep ol’ faithful going:
Ventilate the compressor room to maintain positive air flow. If the compressor is in a confined space, install louvers and thermostatically controlled fans as needed.
Routinely drain the tank. Better yet, install an automatic drain (with test function)
Check oil levels routinely. Add make up oil as needed and perform oil changes on schedule with an oil recommended by the manufacturer. Avoid automotive motor oils, which contain a lot of detergents that leave deposits.
Replace the air inlet filter routinely. You may be able to vacuum it out to extend the replacement interval. Plugged air filters restrict the performance of the compressor and increase operating temperature.
Find and fix leaks on the compressor and in the system all the way to the fittings, hoses and tools at point of use. Listen for leaks and hissing sounds while the unit is off. On the compressor, check the intercooler and its SRV, pressure switch, and the liquid drain on the tank (which some people leave cracked open to avoid liquid build up).
The belt life on most recips can be very long if you take care of them, but excess heat will reduce belt life. Look for wear and cracks that might cause them to come apart. Damaged belts can create more vibration.
Check duty cycle. If the unit is running more than it used to, you could be using more air or there could be water build-up in the tank and you have less storage. Another possibility is ring wear. A pump up test will tell you if the machine is still making air to specification and point you toward the cause.
For more information on piston vs rotary screw compressors check out our infographic or read our blog post on the subject.
You’ve done the research, completed the performance comparisons, created life cycle cost analysis spreadsheets, and maybe even lost a little bit of sleep perfecting your pitch to get the purchase requisition signed. But in all of your planning and number crunching, did you remember to consider how the compressor room location will impact equipment performance? The real estate mantra, “Location, location, location” rings true for getting the energy savings you’re expecting from your compressed air system. For reliable and efficient compressed air performance, consider ventilation, equipment clearance, and the overall compressor room environment. Continue reading “Location, Location, Location: How Placement Impacts Compressed Air Equipment Performance”→