Air compressor continuous run?

My air supply is in stages. One 7.5 hp 3-phase 230v Quincy can usually carry the load. It come on at 90 and runs to 120, or there about. If the demand is bigger, another Quincy gets put on line. I also have a 10 hp. Hydrovane as a back-up. I have yet another Quincy in reserve. I hate not having air! We're looking at #1 that seems to be about 50% duty cycle with just less than 1 minute off time. We're wondering if we would be better off financially running the motor continuously and unloading the valves at high pressure.

One of my ideas was for the lowest mechanic to catalog every air leak and repair them...they add up quick. It seems we can go about a year before they become an issue.

I wonder if you might be better off with one of the 4 running a bit slower on a smaller motor and continuously - ie - 3-4hp - and then use the other 3 as needed when the draw is larger. Don't know for sure, but seems more likely to be efficient to have one pumping all the time (or nearly) than to have it pumping and unloaded and pumping with a bigger motor.

I am prone to overcomplicate things at times, but a setup where you had that, and then as that started to be overcome you switched in a 7.5, and when/if the pair got to pressure you shut down the smaller one and let the 7.5 carry the larger load, unless/until it was unloaded for a long period of time, when you'd switch it off and go back to the smaller one when the pressure dropped again...

Seems like something that a PLC could manage for you most efficiently.

Getting the leaks should help, certainly - that's just money out the window.

I think that it is awfully stressful for a continuous duty motor to start up every 2 minutes. I would look into continuous run or I would get a drive or a soft start.

Can you get a bigger compressor? And sell all this hodgepodge of compressors to pay for a bigger one?

If they aren't already, I would first connect all the tanks as common storage. That will increase your cycling time.

--Andy Asberry--

------Texas-----

"Tom Gardner" wrote in news:cj5Wi.37945$ snipped-for-privacy@newssvr13.news.prodigy.net:

A small plc brick could rotate cycling of the 3 the quincy's, so that you aren't wearing out 1 compressor. This gives the motors time to cool between cycles. I would also have it control the unloaders. As someone else stated all the tanks should be tied together. We do this on the 4 compressors at the plant (3-400 hp, 1-250 hp Sullair screw compressors).

What the others said about managing the load.

But how about reth> My air supply is in stages. One 7.5 hp 3-phase 230v Quincy can usually

VFD, a pressure sensor and a microcontroller to throttle back the motor speed (within limits) to match the air demand?

That could work if he added a fan to cool the motor. at low speed.

suggestion - buy a VFD and an analog ( variable resistance) pressure gauge. follow the VFD circuit example to have a "reference" pressure - the VFD will then act as a servo amp of sorts and as the pump comes to the ref pressure it will slow it down, and if it exceeds it, it will slow it more - so it will keep running, but stay near the ref pressure. this will save lots of wear and tear and also save you the wasted energy (and noise) of an unloader dumping air into the, well, "air" making lots of hissing noises. your cost will be modest, any VFD supplier can help you choose a suitable control

mechanic to catalog every air leak and

We had a 25 hp Quincy where I used to work. When we were doing a system blowdown, it could barely keep up as long as we kept the blowdown pressure under 40 psig. During a normal process run, it would cycle at about 45 second intervals. In talking with our service company, anything that cycles more than 15-20 times an hour needs to run in unloader mode. We reset it to unloader mode and it ran cooler and cut our power consumption by a significant amount.

As to ganging the compressors, set the 7.5 to a 95-120 split, unloader mode, and the second one to a 90-115 split, on-off mode. That way if you sag below 95, the second one comes on to boost capacity. If you watch your power consumption prior to setting the 7.5 to unloader and then after, you will be definately suprized at the savings, especially if you are on a peak demand pricing contract for power.

Craig C.

The fact that your service company cited 15-20 cycles per hour is what I was looking for. I think we'll try unloader mode for a few months and check our power bills. Very, very seldom do we need more than #1 running. I replaced my 40 hp blower with a bunch of 1 hp dust collectors and saved $300/month on our power bill.

That sounds good, although using a smaller motor and running the compressor at a slower speed is also a good suggestion, if that slower speed will satisfy demand most of the time. Do you participate in a demand reduction program? Energy Curtailment Specialists is installing free demand interval meters at our facilities. They aggregate demand reduction and sell it to the NYISO grid. It's a nationwide company, they might offer something in your area.

When I visited the Starrett tools factory, the apprentice who gave me a tour said that each department was being held accountable for its air leaks. The average department found about 30-40, with the worst offenders having over 100 leaks. When they fixed all the leaks, they found they saved about $10000 a year in terms of running their 300 HP air compressor less.

I once worked on a project with Ingersoll Rand. They'd found that a significant consumer of energy in many or most factories is ... leaks! Some of those facilities had energy cost of over $1 million per year just for compressing air. There's one consultant, don't recall his name, who makes a very good living finding ways to save a few percent of that.

At a previous job, I found a guy with an air hose fixed up to blow air at himself for personal cooling. I asked him if he realized how expensive that trick was and he replied he asked for a fan and the supervisor said we couldn't afford it.

Just an example of shop logic, economics and pushback.

Wes

Many tool companies advertise "no power required, just hook it to your air supply". Most people do not realize that operating an air tool costs twice as much in power as operating an electric tool for the same job. We have two 75 hp Gardner -Denver screw compressors with a couple 50 hp screws as backup. With regular oil and filter changes one of the 75 hp compressors has an operating time of 143000 hours on the machine without any repairs - other than a solenoid valve in the control circuit. That is what I call a reliable machine.

After we shut down at night and before the air tank has bled down, I walk through the plant and cry listening to the hissing air leaks. I need to bump it up to top priority.

Brazed heavy L copper pipe, lots of good ball shutoff valves everywhere, lots of padded supports and bracing so it can't vibrate.

For large outfits it's worth the extra effort to set the main line up as a "ring main" in a loop around the room, with three or four shut-offs (or more) around each loop in a logical pattern. That way you can shut down one zone to work on it during the day, while leaving the rest of the plant with air pressure and running. Ball valves are cheaper than lost time for a shutdown.

All take-off tees pointed up, so the condensate in the ring main stays in the ring main, and finds it's way to the drain legs placed at the low spots. But you still put drip-legs and drains at each machine.

Buy the materials and keep them on site - call your friend the Plumber and ask about the "Special rate for slow days".

-->--