Control options for compressors with single phase & 3 phase AC electric motors.

[Tracy]

Auto Drains

Auto Drains seem to be pretty highly sought after. They provide a nice feature, but they tend to be rather pricey. Now that I am starting to learn about how breathing air filtration works, I have another concern, other than purchase price.

I have looked at a couple of small Bauer units recently that had auto drains and automatic pressure shut off switches. When the final pressure set point is reached on these two units, the compressor shuts off, which is all fine & good, but the unloader valves also open & dump the pressure out of the filtration system. Is this not bad for the filter cartridges? Does this not defeat the very purpose of the pressure maintaining valve? Does this not seriously decrease the usable lifespan of the molecular sieve in the filter cartridge?

It dumps the separators, not the final filter housing.

 

[PBcatfish]

It dumps the separators, not the final filter housing.

I was hoping that I was misunderstanding something about the way that they worked. The two I looked at each had 2 unloader valves. One dumped the little cup under the second stage & the other dumped from the fitting at the bottom of the P0 tower. Does that not dump all the pressure out of the filter tower?

I was looking at a Bauer Jr II & a Bauer Utilus 10.

 

[Gone for diving]

There a check valve between , final and water separators

 

[PBcatfish]

There a check valve between , final and water separators

Thanks, I'll look for that.

 

[PBcatfish]

There a check valve between , final and water separators

I'm looking for the check valve, but I'm not finding it.

The unit I'm working with is shown in the last parts manual at the bottom of this page - VARIUS, PURUS, UTILUS 10

Page 11 shown the filter housing. I do not see a check valve pictured or listed. Am I just missing it? Or perhaps is that a feature that the older filter housings lacked?

 

[PBcatfish]

Manual Motor Starters (and cheating with breakers)

Getting back to the original purpose of this thread, I'll post some basic information on manual motor starters.

The most basic legitimate way to turn an AC electric motor on & off is by using a manual motor starter. These are available for both 3 phase & single phase motors. It is possible to use a 3 phase manual motor with a single phase motor if you add a jumper wire.

Some of these turn on & off with push buttons. Some use rotary switches. They all trip out when a predetermined load limit is reached for a short predetermined period of time.

The trip point on most modern manual motor starters can be adjusted by moving a dial. The dial is usually rated in amps. There will be a limited range of amps to choose from. One may have a range of 2-5 amps. Another may have a range of 4.5-8 amps, etc.

The amp dial is usually calibrated for a motor with a 1.15 service factor. If you have a 1.15 service factor motor with a nameplate amperage of 6.3 amps, then you set the dial for 6.3. If you have a cheap motor with a 1.0 service factor, then you are supposed to set the dial a little lower. If you have a 1.25 service factor, then you can legitimately set it a little higher.

A manual motor starter is there to protect the motor from overhearing. Once it trips, you can wait a short time for things to cool down, then reset it & run again. If it keeps tripping, check your amp setting. If it is correct, look for a mechanical bind on the motor load. If that is not present, then the motor may be bad or the supply voltage may be low.

Some can be screwed directly to a back panel. Some mount to a piece of DIN rail, usually 35mm. Many can be mounted either way. It is customary (& often required by code) to mount them in some sort of enclosure, often with the control switch part sticking out. Plastic boxes seem most popular for this purpose.

Most electrical supply houses will have manual motor starters available, but the single piece price to the public is often a little high. For reference, here is one online source that doesn’t gouge your eyes out too badly - https://www.automationdirect.com/adc/shopping/catalog/motor_controls/iec_manual_motor_protectors/manual_motor_protectors_(01_to_63_amp)#sort=undefined asc&start=0

Some people who do not want to spend $50-$75 on a manual motor starter will try to cheat by turning the motor on & off with a panel breaker. In this case, you turn off the breaker that feeds an outlet. You then plug in a cord that goes straight to the motor & then turn the breaker back on to start the motor. While this has been know to work, and ‘m not going to pretend that I’ve never don it in an emergency, this is not recommended. The breaker is sized to protect the wire that goes from the breaker to the outlet. It will not protect the motor from an overload. Also, the breaker was not designed to handle the arc that is created when staring a motor load. Damage is done to the breaker each time you switch on the motor load that way. You might get away with this for a limited amount of time. That amount of time may span 20, 50, or 100 starts, or maybe even more, depending on how big the breaker is & how big the motor load is, but eventually you will kill the breaker if you keep doing this.

Plugging a hot wired motor into a hot outlet does significant damage to the outlet & also damages the plug. This is another practice that is not recommended. In some cases, the plug prongs may weld to the contacts in the outlet & you will not be able to disconnect it after.

The next step up from manual motor starters, is magnetic motor starters.

 

[Tracy]

I was hoping that I was misunderstanding something about the way that they worked. The two I looked at each had 2 unloader valves. One dumped the little cup under the second stage & the other dumped from the fitting at the bottom of the P0 tower. Does that not dump all the pressure out of the filter tower?

I was looking at a Bauer Jr II & a Bauer Utilus 10.

I honestly have zero experience with a p0 tower. They are usually the first thing I pitch when I get a compressor that has one. I believe it has a separator built into it and an internal check valve between it and the filter side. That is why they have two drain valves. I remove them and install a coalescor and a filter stack.

 

[PBcatfish]

I honestly have zero experience with a p0 tower. They are usually the first thing I pitch when I get a compressor that has one. I believe it has a separator built into it and an internal check valve between it and the filter side. That is why they have two drain valves. I remove them and install a coalescor and a filter stack.

Which coalescor & filter stack would you recommend for a small (4-10 cfm) compressor?

 

[Tracy]

Which coalescor & filter stack would you recommend for a small (4-10 cfm) compressor?

I usually use a 16" coalescor and 16 filter stack on a small unit. 10 cfm is a decent sized compressor, depending on volume you are pumping, a 30" stack might make better sense. For a home machine, I like to size the filter stack to your annual CF. It is nice and easy, once a year, pop the filters, clean the coalescor, take an air sample, change the oil, install new filters. It is so much nicer than tearing into it every other day or every week with a p0.

If you are shopping new, something like this is ideal

LAWRENCE FACTOR® | Product Details

www.lawrence-factor.com

I usually use used ones removed from compressors not worth repairing.

 

[tbone1004]

Which coalescor & filter stack would you recommend for a small (4-10 cfm) compressor?

separate units always, and the bigger the better. As big as you can justify/afford. Will minimize the changes of filter and purge cycles on the coalescer. The cost/filter size is not linear since it's just a longer tube, so I would always recommend to go bigger.