Air Compressor 460 volt 20 amp on an 30 amp Breaker

[retirede]

Have connected my share of air compressors . Preferred to use a fusible safety switch with quality 200KIAC rated fuses. Can not remember ever having a problem with any air compressors that shut off at 120 #'s air pressure and only using fuses no more then 150% higher then motor FLA. In some commercial garages they needed at least 135 to 140#'s of air pressure to operate air jacks to lift up loaded trailers so they did not cut off until 150 #'s . In that case had to use a time de!ay fuse rated 175% higher then motor FLA. Had trouble with a couple of jockey air compressors on sprinkler systems where they had the cut in & cut off too close together and air compressors would short cycle ( on & off several times a minute ). You should not have any problem with the existing #6 copper wire. In larger plants where they had several air compressors running at the same time we had tech install think it was an unloaded on at least one air compressor that ran entire production time. At end if day they flipped a switch to return it so air pressure switch controlled it. Had one one a 200 HP screw compressor.

Unless there’s a leak somewhere (or no air reservoir), a compressor that pressurizes a sprinkler system shouldn’t run more than once per day!

 

[kwired]

Unless there’s a leak somewhere (or no air reservoir), a compressor that pressurizes a sprinkler system shouldn’t run more than once per day!

Aren't they primarily used on "dry systems" in places that might freeze if water were standing in the lines?

Your piping is the air reservoir at least to some extent, I would think they don't run the air pressure very much higher than the incoming water pressure, that would be more air that needs to bleed out of the system when there is a situation calling for the sprinklers and on top of that you wouldn't want any more reservoir than necessary either or it would be more air to bleed before water gets to the sprinklers.

I don't know a whole lot of details of what the ins and outs are here but trying to approach this with some logic as well.

I also think running once per day would likely be a sign of leakage in the system and that it likely should hardly ever run at all. I think such systems do have a pressure monitor and will give you a trouble alarm should the pressure be too low which is what would eventually happen if the compressor fails to run when needed.

 

[kwired]

They use the "twin motor" units for where there is only single phase power available and you need higher HP. I used to see them alot but not so much anymore. All of them should have a starting unloader of some type though

Well that also has "twin compressors" If it were "twin motors" that sounds more like two motors driving the same load.

Oops… I “tried”to attach an picture off my phone but too big an file apparently, but an friend commented that “That it’s a twin compressor, so likely no unloader valve “

If it is something like Joethemechanic pictured, that one has an unloader valve for each of the separate compressors.

The little black poly tubing coming off each pressure switch is running to it's respective compressor output line and ties in just before the check valve at the tank. when the pressure switch reaches set point it opens the control circuit and also opens a valve to unload the pressure in that line.

 

[don_resqcapt19]

Aren't they primarily used on "dry systems" in places that might freeze if water were standing in the lines?

Your piping is the air reservoir at least to some extent, I would think they don't run the air pressure very much higher than the incoming water pressure, that would be more air that needs to bleed out of the system when there is a situation calling for the sprinklers and on top of that you wouldn't want any more reservoir than necessary either or it would be more air to bleed before water gets to the sprinklers.

I don't know a whole lot of details of what the ins and outs are here but trying to approach this with some logic as well.

I also think running once per day would likely be a sign of leakage in the system and that it likely should hardly ever run at all. I think such systems do have a pressure monitor and will give you a trouble alarm should the pressure be too low which is what would eventually happen if the compressor fails to run when needed.

Actually it is substantially less then the water pressure. The dry valve is designed so the flapper has a much larger surface area on the air side than on the water side so that the air can be at a much lower pressure and speed the response of the system when a head opens. In some systems the air pressure could be 20% of the water pressure.

 

[garbo]

Unless there’s a leak somewhere (or no air reservoir), a compressor that pressurizes a sprinkler system shouldn’t run more than once per day!

We ( sparkies ) had to run 7 fire & jockey pumps every week and perform quarterly & yearly PM in six buildings. Most were 11 to 13 story buildings with 3 or 4 floors underground. Largest fire pump was 250 HP. Have seen air compressors run several times a hour to maintain air pressure especially in a 50 year old building. Plumbers told us that there is no such thing in a normal pipe section with thousands of feet of pipe that is air or water tight. Numerous times have seen rust at sprinkler joint due to slow leak.

 

[Joethemechanic]

A compressor this size cannot start into a pressurized system without some unloading mechanism. Normally, once you get above 10HP, the compressor will have suction valve unloaders.

Yeah, most of the bigger stuff and the gas/diesel units I have have suction valve unloaders. I can't think that I have ever seen a professionally designed compressor without some kind of unloader provision.

 

[drcampbell]

I've seen one. Just one. A rather special-purpose compressor for a continuous-flow wind tunnel with a 2x2-foot cross section and an airspeed of Mach 3.5.

It was a turbine-type compressor that looked a great deal like the front end of a Boeing 707 engine, driven by a 4000-Hp, 3600 rev/min synchronous motor, with a pressure ratio of probably ~20:1. It didn't have any unloader mechanism because it didn't need one; it's not a positive-displacement device.

 

[retirede]

I've seen one. Just one. A rather special-purpose compressor for a continuous-flow wind tunnel with a 2x2-foot cross section and an airspeed of Mach 3.5.

It was a turbine-type compressor that looked a great deal like the front end of a Boeing 707 engine, driven by a 4000-Hp, 3600 rev/min synchronous motor, with a pressure ratio of probably ~20:1. It didn't have any unloader mechanism because it didn't need one; it's not a positive-displacement device.

Right, those are a different animal altogether.