question about paralleling air compressors

I have a 5 hp Sanborn compressor with air piped around my shop. I'm happy with the setup but would like a tad more capacity. I also have a 3 hp compressor sitting around doing nothing at the moment. Does anyone see any issue with me just paralleling the 3hp and 5 hp compressors. They would end up at opposite ends of the shop. Thanks in advance.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Here's what I think.... It would work, but you would have to adjust the pressure on/off switches to be the same. If not, then only one compressor would be doing all/most off the work. (unless you draw down on the tank alot) And have the range between low and high set far enough apart where the two compressors don't "buck" the motors. I'd just pipe in the extra compressor tank and not plug it in to AC- that would get more capacity. Save the motor for a "hot swapable spare" when the 5hp goes bad.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Now do you see the benefits of cross-posting, not multi-posting ?
(this same question is in rec.metal - got exactly the opposite answer)
I'd set the pressure switches a few psi apart. If you try to start both motors together, you're likely to pop the workshop fuse. Compressors take a lot of current on startup.
(Our workshop has a poor supply. Run the plasma cutter too high and the fuse blows when the compressor starts up)
-- Die Gotterspammerung - Junkmail of the Gods
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If he needs extra capacity, they both will be running while he needs it. He can shut the other off when he doesn't need it.
How do two motors pumping air buck each other? Got me.
You should set the cut on of one of them a bit lower. That way the other will run almost all of the time, while the other only comes on when the pressure really gets drawn down. -- Jim in NC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Why bother?
Capacity will increase with just another tank.

By buck I mean more frequent short duty cycles and more wear on the motor. Got me. (common to light bulbs, cars, electric motors, computers compressors....short duty cycles = early death)

The one set lower will still do most of the work. (unless you're using air chisels and 10 ton lifts for woodworking)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Overall CFM will not increase with just another tank. You need another pump to put air into the tanks faster, so you can drain it faster without running out. Just adding another tank will cause slower on/off cycles for the one motor that runs (i.e. takes longer before it kicks in, but runs longer before it stops).
If you use more CFM than the primary pump can replace, eventually the pressure will fall below the cut-in for the secondary pump, and you'll increase the CFM going into the tanks. If this new CFM now exceeds the demand, eventually the tanks will fill up. If not, at least you'll have less time to wait for the tank to refill.
Note that they make tanks with dual pumps, which operate just as I've described.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
christalmighty did the original question state capacity and not cfm or pressure.......
writes:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The original post talked about the HP ratings of the two compressors, and never mentioned the tank sizes. One would infer that the OP was interested in increasing the CFM capacity, not the storage capacity.
If the OP was interested in storage, the OP would have mentioned tank sizes and not HP.
If the OP was interested in PSI, the OP would have asked about changing the pressure switches.
And even if you're narrow-minded, the rest of us want to be helpful and provide a wide range of information so that the OP can make an informed decision.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You have it backwards. Higher set will shut off last on buildup, and first to cut on, on pressure use.
Done that way, no bucking.
I do this all the time. Do you? -- Jim in NC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No problem. I do just that when I need to. Keep them both hooked up, but only turn both on when you need it. You can use the extra storage that way.
-- Jim in NC
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Nope, I used to do it all the time before I bought a larger compressor. I just set one to kick in a few PSI less than the other. That way only one would run when air usage was low, but the second would kick in to help keep up when needed. Greg
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

many multiple compressor systems to run as you describe. One suggestion would be to switch then on independently unless you need all the capacity. That way you can run each machine occasionally rather than have the machine with the lower setting sitting idle for a long time.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Terry Mayhugh wrote:

I don't see a problem as long as both compressors operate within the same pressure ranges.
I can see where air from one compressor may damage the other compressors cut off switch if the one compressor makes significantly more pressure.
--
Mark

N.E. Ohio
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Just remember that unless you use enough air to get the reservoir pressure below the "on" setting of BOTH compressors, only the one with the higher "on" setting will ever run. The other will only act as an additional tank under most circumstances. In industrial settings with multiple paralleled compressors the controls are often interconnected so that they all come on or alternate or otherwise share the actual running time.
--

Larry Wasserman Baltimore, Maryland
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.