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Discussion Starter · #1 ·
I need some advice about compressors and storage. For the past 3 years I have gotten by with a cheap compressor thats loud and slow/low Cfm. My shop is entirely hobby related.

Recently I purchased another compressor, but this time I bought the cylinder type not vibrator type.

Either compressor will work for me 95% of the time. But that 5% is frustrating.

One compressor has a working presure of 150 psi, the other 175psi. My plan is to basically T off of the safety valves and one leg goes to the safety valve and the other joins the two systems. Neither compressor exceeds 140psi. I will also adjust the start/stop pressures so that the quieter compressor starts at say 100psi, and the loud one at 90psi.

With those settings, in theory I will be drawing from twice the stored compressed air, and the 95% of the time The quieter compressor will maintain my pressure. Then when I am using the high cfm tools bothe compressors will kick in to maintain the pressure.

My question is "is connecting the 2 compressors together like this safe. Keep in mind both compressors will have valves on the connecting lines, and bothe safety valves will remaint in place...
 

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Sawdust Maker
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More information is needed to answer your question. How much pressure and cfm is do you need for the tasks at hand? What kind of tools are you using. Die grinders, D/A sanders, air files and tools like that require a lot of cfm. Typically 20 cfm or more. Especially if you want the pump to be able to catch up while using any of those tools. If you are just spraying, then you don't need nearly as much cfm. Pressure is just as important, and depends on what tools you are trying to run with your compressor. There is no replacement for volume either.

I personally have a 80 gallon 5 hp. 21 cfm 175 psi dual stage compressor, and I wouldn't be able to get away with any less. You may not need nearly as much as I do. That's why we need to know what you want to run with yours to be able to better answer your question.

Mike Darr
 

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Discussion Starter · #4 ·
Here is a link to the first compressor (VERY loud). http://www.homedepot.com/p/Husky-33...ressor-F3S33VWD/202719351?N=c27p#.UaAar8u9KSM

And here is the link to compressor #2 http://www.harborfreight.com/2-horsepower-29-gal-150-cast-iron-vertical-air-compressor-68127.html

PLEASE keep in mind this is a home shop purely for hobby use... Also problem #2 is that I have only 1 220v outlet, and one of the tools that my old compressor can't keep up with is my Plasma cutter...

My main issue is also not CFM, it's noise. While I come up short on CFM occassionally, the wait for the compressor isnt usually a big deal. BUT when I am working with high CFM tools, the noise is not only uncomfortable, but psycally draining...
 

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Sawdust Maker
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Here is a link to the first compressor (VERY loud). http://www.homedepot.com/p/Husky-33...ressor-F3S33VWD/202719351?N=c27p#.UaAar8u9KSM

And here is the link to compressor #2 http://www.harborfreight.com/2-horsepower-29-gal-150-cast-iron-vertical-air-compressor-68127.html

PLEASE keep in mind this is a home shop purely for hobby use... Also problem #2 is that I have only 1 220v outlet, and one of the tools that my old compressor can't keep up with is my Plasma cutter...

My main issue is also not CFM, it's noise. While I come up short on CFM occassionally, the wait for the compressor isnt usually a big deal. BUT when I am working with high CFM tools, the noise is not only uncomfortable, but psycally draining...
As far as noise control, I would either wear hearing protection while it's running or locate the compressor in another room that is sound deadened. Nature of the beast.

Mike Darr
 

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Discussion Starter · #6 ·
Relocating the compressors is not an option. Neighbors and cit ordinences prevent outside. The fiance prevents in any room other than Garage.

Hearing protection is the current solution, but if you live in Texas and suffered a summer here you would understand why I would prefer to avoid the ear plugs....

My main issue is safet first, functionality second and safety third....
 

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If it were me I would use one compressor or the other and not link them. I don't know what you would need 140 to 175 psi doing woodworking. I sometimes use the higher pressure sandblasting but the rest of the time I keep the pressure regulated down to 100 psi.

For a smaller compressor I mostly use a speedaire compressor which was made by campbell hausfield. It runs quiet enough you can carry a conversation with someone standing next to it. They are available on craigslist every day in the Dallas area. I bought one a couple of weeks ago for 50 bucks for parts to restore mine. All that was wrong with it was the tank had a leak. Probably another fifty dollar compressor would have a good tank and a bad motor.
 

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Sawdust Maker
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If it were me I would use one compressor or the other and not link them. I don't know what you would need 140 to 175 psi doing woodworking. I sometimes use the higher pressure sandblasting but the rest of the time I keep the pressure regulated down to 100 psi.

For a smaller compressor I mostly use a speedaire compressor which was made by campbell hausfield. It runs quiet enough you can carry a conversation with someone standing next to it. They are available on craigslist every day in the Dallas area. I bought one a couple of weeks ago for 50 bucks for parts to restore mine. All that was wrong with it was the tank had a leak. Probably another fifty dollar compressor would have a good tank and a bad motor.
I regulate my compressor to 100 psi. It turns off at 175 psi and turns back on at 125 psi. Having more volume, psi, and cfm means the compressor will not have to run as long or often. That's a plus to me. Lower electric bill, less wear and tear on the compressor, and I don't have to hear it run as often. I also don't want to stop working to wait from the pump to fill the tank again.

Mike Darr
 

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The New Guy
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One compressor has a working presure of 150 psi, the other 175psi. My plan is to basically T off of the safety valves and one leg goes to the safety valve and the other joins the two systems. Neither compressor exceeds 140psi. I will also adjust the start/stop pressures so that the quieter compressor starts at say 100psi, and the loud one at 90psi.

With those settings, in theory I will be drawing from twice the stored compressed air, and the 95% of the time The quieter compressor will maintain my pressure. Then when I am using the high cfm tools bothe compressors will kick in to maintain the pressure.

My question is "is connecting the 2 compressors together like this safe. Keep in mind both compressors will have valves on the connecting lines, and bothe safety valves will remaint in place...
A question that's right up my alley. I'm a pressure vessel inspector for oil refineries and chemical plants all over the continent.

You can connect the two bottle together but the bottle with the lower MAWP (max allowable working pressure) is the one that limits your pressures. You can't have 150psi in one bottle and 175 psi in the other. They're going to be effectively one bottle from a pressure standpoint. (You seem like you already knew that, which is good) The relief valve on the higher pressure bottle will be useless so there's no need to leave it there, unless you want to turn it into two separate compressors at a later time. You don't have to remove it, just bear in mind that it's useless.

What you need to be careful with is the one relief valve that remains. Now, instead of having to relieve pressure faster than the one compressor it was paired with to keep the system safe, it has to relieve pressure faster than the two compressors combined. It's very likely that it can, but you might want to test it out and make sure. The manual that came with them may specify maximum CFM of the relief valve. Basically, CFM of tank 1 + CFM of tank two must be less than CFM of the smaller relief valve at the relief pressure. To be safe, make certain your relief valve is designed for that maximum possible CFM it will have to relieve. I can't stress that enough, you want to be certain. If it can't, the valve may open and try to relieve the pressure, but the pressure can still build if the compressors build faster than the relief valve relieves. I've seen the damage that can be caused by overpressured pneumatic systems. It's ugly. Easiest way to test the relief valve is to connect them, turn them on, then open the valve manually and verify that pressure goes down, not up when it's around 150 PSI and both compressors are running. It'll be loud, so wear hearing protection.

I just clicked the links, and both of those bottles are rated at 150 PSI. The relief valves should pop very close to each other, so you should be good. Just make sure you're not trying to backfeed a check valve or anything crazy like that.
 

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Discussion Starter · #11 ·
My main reason for keeping both blow off valves is safety. My logic is that its unlikely that both would fail at the same time, and if one failed the legal buffer would allow the second tank to still be safe.

Yes I do understand the safety aspect, and thats why Im posting. My logic with this configuration is that by linking the high pressure ports, I affectively double my storage capacity. Then when I exceed storage capacity, the quieter of the two compressors will handle most of the load. And then in the rare occasion where the quieter compressor is not enough the louder of the two compressors will kick in... Now of both cannot keep up I am going to deal with the combined noise of both compressors running...
 

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The New Guy
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Yep, you'd basically double your stored volume vs using only the quieter one. You'd also have better flow (higher CFM) assuming your air hose isn't limiting your flow. It will obviously take longer to refill the doubled volume, so your quieter compressor will run longer than it did before to refill the two bottles. Your idea is sound in design. It's as simple as plumbing in a few fittings. I'd link the two with a high pressure hose instead of rigid piping. Splice in a T with a quick connect fitting on each tank and a hose between them. That way if you bump into one of the bottles you don't have to worry about over stressing and breaking the piping. The only problem with it I can see is if you don't know how to properly connect the two. A check valve reinstalled backwards can be a major problem.

*Disclaimer - I'm possibly thousands of miles from you and won't verify that your instillation is proper, so do what you want, at your own risk.
 

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Old School
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My main reason for keeping both blow off valves is safety. My logic is that its unlikely that both would fail at the same time, and if one failed the legal buffer would allow the second tank to still be safe.

Yes I do understand the safety aspect, and thats why Im posting. My logic with this configuration is that by linking the high pressure ports, I affectively double my storage capacity. Then when I exceed storage capacity, the quieter of the two compressors will handle most of the load. And then in the rare occasion where the quieter compressor is not enough the louder of the two compressors will kick in... Now of both cannot keep up I am going to deal with the combined noise of both compressors running...
I'll try to keep this simple. I've tried linking two compressors intact as you are suggesting, and I've hooked two compressors to one tank. In basic terms, I think about compressed air like water in a hose. CFM is like how much water comes out of a hose, and PSI is how fast it comes out.

Compressors are pretty basic and they all operate with the same principles. You have a pump that forces air into a tank. The pressure in the tank tells the motor when to stop pumping. In essence, if you change that pressure setting, you effectively alter the efficiency of the compressor as for its output and duty cycle.

If you try to link the two at the valve, the check valve will sense the compressed air in the tank, or lack of it and either shut off or continue to run. In this case, your smaller compressor will add little to nothing as a "filler". You could run into safety problems. The motor on a compressor is matched to the output. If there is a change to the sensed pressure (if it is manually changed from factory settings), the motor can be stressed and run too long to achieve the pressure state of the "cut off" pressure, and overheat, and possibly start on fire. I've seen that happen.

It's not rocket science, as there are no rockets involved. As you can tell I'm not advocating doing a union. The best answer was already suggested which is to use a compressor more suited for your needs. Actually, I would just use your larger compressor (the oil lubed one), and contend with pacing yourself.







.
 

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A question that's right up my alley. I'm a pressure vessel inspector for oil refineries and chemical plants all over the continent.

You can connect the two bottle together but the bottle with the lower MAWP (max allowable working pressure) is the one that limits your pressures. You can't have 150psi in one bottle and 175 psi in the other. They're going to be effectively one bottle from a pressure standpoint. (You seem like you already knew that, which is good) The relief valve on the higher pressure bottle will be useless so there's no need to leave it there, unless you want to turn it into two separate compressors at a later time. You don't have to remove it, just bear in mind that it's useless.

What you need to be careful with is the one relief valve that remains. Now, instead of having to relieve pressure faster than the one compressor it was paired with to keep the system safe, it has to relieve pressure faster than the two compressors combined. It's very likely that it can, but you might want to test it out and make sure. The manual that came with them may specify maximum CFM of the relief valve. Basically, CFM of tank 1 + CFM of tank two must be less than CFM of the smaller relief valve at the relief pressure. To be safe, make certain your relief valve is designed for that maximum possible CFM it will have to relieve. I can't stress that enough, you want to be certain. If it can't, the valve may open and try to relieve the pressure, but the pressure can still build if the compressors build faster than the relief valve relieves. I've seen the damage that can be caused by overpressured pneumatic systems. It's ugly. Easiest way to test the relief valve is to connect them, turn them on, then open the valve manually and verify that pressure goes down, not up when it's around 150 PSI and both compressors are running. It'll be loud, so wear hearing protection.

I just clicked the links, and both of those bottles are rated at 150 PSI. The relief valves should pop very close to each other, so you should be good. Just make sure you're not trying to backfeed a check valve or anything crazy like that.
Thank you.

I am glad to see that someone finally answered his question.

George
 

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Now that the question has been answered it is time t digress slightly. I agree with Cabinetman that the course of action that I would follow is to use only your best compressor. It may occasionally take you a little longer to do a job, but it is far less complicated.

George
 

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Rustic furniture
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Noise issues can be solved by isolating the compressors in a sound insulated box/closet/enclosure in the shop,,,but you need to have access to air changes via a vent to outside for cooling. Also a access door for adjusting the pressures, unless you route the fittings outside of the box.

I don't like loud compressors, especially when I'm spraying paint. It somewhat startles me when handling a paint gun, and I tend to jerk when it kicks on and I'm concentrating on spraying.
 

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The easiest way to connect the two compressors is wire both of them to a magnetic switch and set the pressure switch to the pressure rating of the smaller compressor. That way they would both run at the same time and not exceed the pressure rating of the smaller unit. The bad is they wouldn't be portable anymore.
 
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