Dual Air Compressor setup

[Earl Weiss]

Running dual 5HP 80 Galllon 5Hp compressors at locations. Tunnels, some with Mechanic shops using same compressors.

For decades one has had both compressors running off a single pressure switch. Others have had 2 pressure switches. Blew one compressor and the company doing the replacement (Champion 5 HP 80 Gallon) says the single pressure switch set up was wrong. So he instals the new one with it's own switch.

With seperate pressure switches one compresor runs 90% of the time. It will kick on and start building pessure before the second switch drops below the start level. The one compressor now needs t o bring both tanks up to the shut off level. So, what is the theory?

Is it better (easier on the compressor) to have one compressor run for 20 minutes than 2 compresors for 10 minutes?

I know with some mechanical stuff frequent starts and stops are worse than longer run times but this seems counter intuitive.

 

[MEP001]

The motor and starters are what usually fails first on a compressor. It also greatly increases your operating cost to start a motor more than you need to. I don't see how starting the compressor is in any way harmful to the pump, and as long as it's not getting too hot it should come to no harm running continuously for 20 minutes vs. 10. It definitely makes sense to have one do most of the work and have the other serve as a backup if demand is too high for one or if one breaks down.

 

[pitzerwm]

I've been told that its better to have them run a longer time frame than a short time frame. It would appear that one of the switches is set different than the other. If you could get them set the same that would be a trick, maybe wire them in series, would force both of them running the same amount of time.

 

[Earl Weiss]

Came here for opinions fiorst because in the past I have gotten some bad info from air compressor people who know compressors but not car washes.

Anyway got a hold of the guy at the company who just did the work. They no longer use a single switch for 2 compressors because theoreticaly something could fail and a tank would be over pressurized if someone shut the connection between the 2 tanks, and the pressure relief valve failed as well.

He did confirm that both compressors should run together and there is a way to wire the switches together and they will be making the correction.

If we are running hard and the shop is being used one compressor may just barely keep up. This means it could run for 20 minutes or an hour or more and the other one would never kick on. With both running they will easily catch up and re pressurize to the shutoff level.

If one fails we can temporarily tell the shop to cut back on air tool usage until repairs are made.

So, this is the best way to go.

 

[newhampshiretech]

another item

Just an FYI , if you wanted equal run time on the compressors. They do make oscillating switches that will turn on one compressor then switch back and forth every time the need for air is requested via the pressure switch.just so u don't have one sitting idle forever. Very unlikely but if the secondary sat unused for a very long time could seize up. I realize it's a long shot.... Don't ask me how I know ;(

 

[robtl]

Just an FYI , if you wanted equal run time on the compressors. They do make oscillating switches that will turn on one compressor then switch back and forth every time the need for air is requested via the pressure switch.just so u don't have one sitting idle forever. Very unlikely but if the secondary sat unused for a very long time could seize up. I realize it's a long shot.... Don't ask me how I know ;(

They make what they call a "lead-lag" controller that switches the two back and forth at a set time, you might google lead-lag controller and find what you need.

 

[MEP001]

Just an FYI , if you wanted equal run time on the compressors. They do make oscillating switches that will turn on one compressor then switch back and forth every time the need for air is requested via the pressure switch.just so u don't have one sitting idle forever. Very unlikely but if the secondary sat unused for a very long time could seize up. I realize it's a long shot.... Don't ask me how I know ;(

I figured it's not good for a compressor to sit and not run for a long time. About once a month I shut off the main compressor and let the smaller one run for a day. It's not hard to remember to do since the main one is so frickin' noisy.

 

[Earl Weiss]

Switching back and forth for seperate but equal run time would not work for me. I know because in the past sometimes if one compressor stopped working the other would never catch up or catch up and shut down / cool off for such short periods it would overheat.

Anyway, the installer came back and wired the presure switches in seres so they both run together.

 

[Whale of a Wash]

For the extra demand charges on electricity by running them both at the same time, it would make sense to switch to a rotary screw compressor that is about as loud as a vacuum cleaner and uses 40% less energy, they are also built to run constantly. I know a little expensive, but savings on electricity would pay for it.

 

[Earl Weiss]

For the extra demand charges on electricity by running them both at the same time, it would make sense to switch to a rotary screw compressor that is about as loud as a vacuum cleaner and uses 40% less energy, they are also built to run constantly. I know a little expensive, but savings on electricity would pay for it.

Haven't though to that. Since my Tunnel may run 150HP for blowers and power packs does the extra 5 HP really add that much demand?

 

[Whale of a Wash]

Probably wouldn't matter much--demand is probably not noticeable at your place. That is some amazing dryer power-I think the most i had seen was 100HP of drying.

 

[dewey9876]

Kinda on the same subject. I have an old compressor with a bad pump. I was thinking of plumbing the tank in with the new compressor for more volume.
1. Is this a good idea?
2. If so, what is the best way to plumb it in?

Thanks

 

[MEP001]

1. Is this a good idea?

Yes, if your new compressor is rated for continuous duty cycle. If it's not it may overheat and damage the pump.

2. If so, what is the best way to plumb it in?

I have two compressors just tee'd together at their outlets so they share the tanks. It shouldn't matter how they're plumbed together as long as there's not a device like a water separator on the line that would let air flow in the wrong direction when air comes from the extra tank.

 

[Earl Weiss]

Probably wouldn't matter much--demand is probably not noticeable at your place. That is some amazing dryer power-I think the most i had seen was 100HP of drying.

The drying is 7 Fifteen horse motors. Hydraulic Power packs are the other 35 or so and then 10 HP total for the Compressors.