Air Compressors - What IS 100% duty cycle? - Long Read - FS Curtis = Garbage

TL;DR
We bought this air compressor on its' advertising stating that "Built for 100% Continuous Duty." After 1.25 years, 90% of the time being hard down and nothing but headaches from the service people, new Curtis Service Rep says:

"We have spoken to the marketing and technical department about the duty cycle. Here’s what’s true, the units have a 100% continuous run cycle, when sized properly the units can operate 100% of the time with 75% of the time loaded and 25% of the time unloaded. If the way the Quincy was operating during our visit is any indicator of air demand on a typical day, the units were undoubtably running 100% of the time loaded which can lead to excessive wear and premature failure. I was able to confirm the units are pressure lubricated. I apologize our lack of knowledge with these pumps didn’t aspire confidence, but we are going to uphold any commitments we make and you can hold me accountable."

I'm scratching my head here...this is a Start-Stop machine...so if the motor is on, that means we need air and the pump is Loaded. Does this make any sense?

The Long Version

My place of employment purchased a FS-Curtis ML-20 Duplex Compressor March of 2018, and we didn't install it or start it up until May 2018. The install was checked out and signed off by a Curtis technician for our extended 5-year warranty. Since then it has been broken down 95% of the time. During what appeared to be a cleaning house of personnel from the Curtis distributor in the SoCal area, we had to go through quite the process getting the new folks handling our warranty repairs for our lemon up-to-speed. The unit did not come with any type of run-hour meters, so I installed those to keep track of oil changes, etc. The unit didn't even make it to the 50-hour mark, let alone the 500-hour mark for its first oil change (per the manual) before it started eating intake valves, etc. Both pumps on the unit have had multiple full rebuilds. The control enclosure vibrates so bad that it has destroyed 3 control transformers by shearing off the metal feet, one of the motor contactors burned up, and after having the last warranty work completed back this September (the entire unit had been down for over 8 months waiting for the distributor to get their act together), I turned it on for the second time since then (to test new plumbing) and a flexible stainless line from the high-pressure discharge port on the #1 pump to an after-cooler failed catastrophically. Luckily I had just stepped out a minute prior and didn't still have my face in the vicinity where it had been previously listening for leaks and knocks.

Of course, I have wanted the entire unit taken away and a refund given since day one, but was overruled by the bossman, and now the Distributor will keep coming our to "fix" it, but will not take it back. I was pretty fed up with the past year of non-performance and having to rent compressors, but after it trying to kill me recently I am tempted to just cut it up into pieces and craigslist the remaining parts.

In all, there have been over 25+ visits by techs from two different locations working on this thing.

Has anyone had a similar experience?

Ive never heard of any kind of industrial compressor that wasnt capable of running at 100% duty cycle provided suitable motor and cooling........less puts it in the home shop class.....Ive worked on compressor maintenance for years,recips were mostly antiques,and totally reliable,newer were all screws...the only issue ever is insufficient cooling in enclosures ,with maybe fan ventilation ,and outside air intakes..... and as for 100% duty cycle ,but not at 100% loading is just nonsense........I say you are lucky it aint your money......Anyhoo,why not a good quality screw?..Plenty of second hand units available...

Were it me..which it ain't, I would certainly "kill" the person the spec'd this compressor way before I "killed" the Curtis folks. If the boss was too dumb to know about the CFM needs of your facility then the Curtis guy should have..so on second thought, "kill" them both!!

Stuart

Since the boss doesn't want to buy a proper machine: Just find a great one at one of the rental places and rent it on a yearly basis. As much as that Curtis is down it will probably be cheaper than only renting it when you need to. Less transport and administration. Maybe you can get a deal where you pay a fixed amount plus something for each hour run. Make some kind of connection so that you only have to flip a couple of valves and turn on the rental when the Curtis brakes down. Seems the easiest way around the problem.

I'm currently shopping for an air compressor. I started a thread here, asking about the quality of the new Quincy compressors, but learned that most of those are not full cast iron compressors and have reed valves.
So, I began looking at FS Curtis compressors, thinking they were better, but after reading your post above, I'm obviously doubting that.

After reading your post, I began reading about the duty cycle on air compressors.

The Atlas Copco site has a good explanation of duty cycle for piston compressors:

What is piston compressor duty cycle? - Atlas Copco Australia

However, I'm not understanding the loaded vs unloaded comment by FS Curtis. Are they saying that it spends too much time running at 100psi and above?
Obviously, if your using enough air that the tank is nearly empty all the time, its less load on the compressor if its running at 50 psi and trying to keep up as opposed to using just enough air that the compressor is always running around 100psi.

I think "full load" means that the compressor is running at 100 psi or above, but I'm not positive about that.

I'm just trying to learn for my own sake, not trying to answer any questions. Feel free to correct me if I'm wrong.


btm

I don't understand what your usage is or how much the compressor runs. A compressor is not designed to run 'on' 24/7. GIve us an idea of what duty cycle it runs so we can have an idea if you are on the right track. My gut tells me about 25-40 percent compressor on time on a given day would be an acceptable duty cycle for a properly sized recip compressor. Maybe others disagree, but above that I think you needed a bigger compressor. Essentially an industrial compressor ought to be able to run until it cannot keep up without 'failing'

that said an undersized compressor might see heat, oil consumption, water[from the heat] but not the kind of failures you are seeing

the things you mention seem vibration related

Nothing with pistons and a crank is gonna run at 100% 24/7 365 for 20 years. So what was your real expectation?

As others note, if you want 100% all the time, get a centrifugal compressor. Even they need maintenance, so again, define your duty cycle.....

The ONLY part of an electric-driven compressor that will run at 100% for 20+ years is the electric motor. The rest....something is gonna break.

As for your particular compressor, it sounds like a born lemon that was also being squeezed too hard and all the juice ran out...

btm said:

However, I'm not understanding the loaded vs unloaded comment by FS Curtis. Are they saying that it spends too much time running at 100psi and above?

Click to expand...

Once you get into larger electric motors, say 20 hp and larger, there is often a maximum number of starts per hour. Smaller motors may be 6, larger may be 2 or 3. So a large recip compressor will have a motor and compressor that runs continuously. The compressor will be idling until air is required, then it will start to pump. Often, the control for continuous running is a valve on the oil line to the air valves.

So Curtis was saying the motor is 100% run, but the compressor should be compressing air only 75% of the time, and running unloaded the other 25%.

btm said:

I'm currently shopping for an air compressor. I started a thread here, asking about the quality of the new Quincy compressors, but learned that most of those are not full cast iron compressors and have reed valves.
So, I began looking at FS Curtis compressors, thinking they were better, but after reading your post above, I'm obviously doubting that.

After reading your post, I began reading about the duty cycle on air compressors.

The Atlas Copco site has a good explanation of duty cycle for piston compressors:

What is piston compressor duty cycle? - Atlas Copco Australia

However, I'm not understanding the loaded vs unloaded comment by FS Curtis. Are they saying that it spends too much time running at 100psi and above?
Obviously, if your using enough air that the tank is nearly empty all the time, its less load on the compressor if its running at 50 psi and trying to keep up as opposed to using just enough air that the compressor is always running around 100psi.

I think "full load" means that the compressor is running at 100 psi or above, but I'm not positive about that.

I'm just trying to learn for my own sake, not trying to answer any questions. Feel free to correct me if I'm wrong.


btm

Click to expand...

We have a large duplex 5120 Quincy that the Curtis was supposed to supplement, backup for maintenance, etc. It has been rock solid since 2012, besides a suction valve cracking on the 1st day it was being run-in by the Quincy tech. It ate the valve disc, which migrated quite quickly through the head and destroyed both pistons and the bores. Needless to say, that pump got removed that day and a brand-new replacement was in its place in 72 hours. The Quincy is also a start-stop control system with a toggle that alternates between the lead and lag pump. It is rated for 100% continuous duty as well.

"Full load" refers to the compressor suction valves being in a closed state, generating compressed air. Quincy provides control options where the compressor can run continuously then load and unload as air demand increases or decreases, much like a variable screw. Ours does not have this and only starts unloaded, then the unloader towers close, allowing air to pass to the high pressure side and create 50+psi air. As for the Curtis, nothing I have seen in the literature for this unit has a continuous run - auto load and unload system. Either way, if we are running past its true spec, then nothing would be different.

We use easily use 100 CFM @ 120psi regularly (depending on time of day, shift breaks, schedule) due to one of our production processes that has only grown over the years and are indeed needing a screw style compressor to feed that area of our plant. The bossman went with what he knew at the time...that, and before I took over this duty, no real air audit had been performed up until now.

gbent said:

Once you get into larger electric motors, say 20 hp and larger, there is often a maximum number of starts per hour. Smaller motors may be 6, larger may be 2 or 3. So a large recip compressor will have a motor and compressor that runs continuously. The compressor will be idling until air is required, then it will start to pump. Often, the control for continuous running is a valve on the oil line to the air valves.

So Curtis was saying the motor is 100% run, but the compressor should be compressing air only 75% of the time, and running unloaded the other 25%.

Click to expand...

Our Quincy is a duplex 25hp. The manual states that the motors should not start more than 6 times per hour. If I was forced to use a recip and was there when we 1st got the Quincy, I would have spec'd the control variant to be start stop or continuous run.

As for the Curtis, they (AFAIK) don't provide a continuous run setup for this package (even though if could be setup for it). It is rated @ 158.6 CFM @ 175psi, 79.3 CFM if one pump is running. Nothing in the literature I have found breaks down any difference between the motor duty cycle and pump.

gustafson said:

I don't understand what your usage is or how much the compressor runs. A compressor is not designed to run 'on' 24/7. GIve us an idea of what duty cycle it runs so we can have an idea if you are on the right track. My gut tells me about 25-40 percent compressor on time on a given day would be an acceptable duty cycle for a properly sized recip compressor. Maybe others disagree, but above that I think you needed a bigger compressor. Essentially an industrial compressor ought to be able to run until it cannot keep up without 'failing'

that said an undersized compressor might see heat, oil consumption, water[from the heat] but not the kind of failures you are seeing

the things you mention seem vibration related

Click to expand...

I believe from others here at work that we originally were using around 50-75 CFM on average during our busiest shift approx 8 years ago. Since I have been here (4 years) we have grown (most likely outgrown) our original air audit. I think what is happening is that we spend alot of time in that 80 - 110 required CFM range which puts us just over what our Quincy can deliver full out, it is rated to provide 200psi continuously. The Curtis literature says that it can do 158.6 CFM @ 175 Psi, and even says that it is ideal in place of a smaller rotary in that it can run intermittently AND 100% continuous duty.

I have asked all the techs who have visited and the service managers who have been here about the vibration the Curtis exhibits and they all say it is normal. Go figure. I agree that much of the Curtis failures are definitely vibration induced.

GregSY said:

Nothing with pistons and a crank is gonna run at 100% 24/7 365 for 20 years. So what was your real expectation?

As others note, if you want 100% all the time, get a centrifugal compressor. Even they need maintenance, so again, define your duty cycle.....

The ONLY part of an electric-driven compressor that will run at 100% for 20+ years is the electric motor. The rest....something is gonna break.

As for your particular compressor, it sounds like a born lemon that was also being squeezed too hard and all the juice ran out...

Click to expand...

I agree that expecting to run a machine 24/7/365 and thinking we would get 20+ years out of it (like our 3 ancient Quincy's that weren't even taken care of - but also didn't run nearly as often) is foolish.

This machine was definitely a lemon that was then put in a marginal situation (as to load, not environment) that it instantly started to fold. If my time and the boss's money were no object, I would be real interested to have the complete unit torn down by an outside 3rd party and checked for balancing, internal issues, etc.

I don't seem to get the gist of this thread. A compressor was sized by folks that had absolutely no idea of what they were doing, it failed and now someone else is to blame. Maybe I have it wrong though!

Stuart

They advertized it at 100%, and running it has wrecked it several times. 100% is 100%. I would get a lawyer.

atomarc said:

I don't seem to get the gist of this thread. A compressor was sized by folks that had absolutely no idea of what they were doing, it failed and now someone else is to blame. Maybe I have it wrong though!

Stuart

Click to expand...

You may be right about it being undersized. Even so, it began failing less than 50 hours into being put into use (it wasn't running full time) and was purchased on the advertised 100% continuous duty cycle being understood as 100%, not 75%.

I have a quincy 325-7 from 1961 that was the ORIGINAL air compressor at my previous employer.
Was setup for full time run, load\unload. Ran that way for over 35 years with nothing but oil changes.
It sat for a long time in the upstairs of the owners barn.

I bought it a couple years ago, and reconfigured it to start\stop with a vfd and external pressure switch.
Its been running here without a glitch for 3 years now.

Its a much smaller compressor, but frankly, Im shocked to hear about the vibration and failure of that curtis unit.

Been looking for something more modern to replace it, but after reading all the issues with newer models, Im hesitant.