Subject: [Q]: Gas powered air compressor

From: [email-masked] (Stuart Lewis)
Date: Fri, 7 Jun 1996 15:58:53 GMT

A tap of the collective wisdom...

I have the opportunity to purchase a used, 12 horse Kohler powered,
2 stage, Campbell-Hausfeld compressor.  The price is right but I
have a couple questions that, perhaps, can get answered here.

The only thing that keeps me from buying it immediately is that it
is only a 30 gallon tank.  While the rated cfm is really high, what
I want to know is can I run a pressure sand blaster, da sander, etc,
etc, without encountering a high cycle rate (even though it's gas
powered, I think it has a 75% duty cycle do to cylinder heating).
Otherwise, the solution would be to purchase a 60 or 80 gallon tank
>from  say Grainger, and re-fit the powerhead and compressor to that
- then it's not so good a buy.

Thanks in advance,

Stuart Lewis
[email-masked]

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From: Robert Bickers <[email-masked]>
Date: 9 Jun 1996 18:13:54 GMT

>- then it's not so good a buy.
Sense the motors running all the time anyway I feel a high duty cycle is OK and if the CFM is 
suficient for your needs go for it, usual caveats apply. 
PS if do don't buy it will you e-mail me the particulars as I might be enterested. Thanks Bob

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From: [email-masked]
Date: Sun, 09 Jun 1996 23:34:23 GMT

>powered, I think it has a 75% duty cycle do to cylinder heating).

You only buy yourself a couple of minutes of extra capacity with the
large tank.  Overall, the capacity of the compressor must match or
exceed the usage, or you will run into problems.  A simple equation
rules:

Inflow = Outflow + Accumulation

If the outflow exceeds the inflow, then the Accumulation can only
supply the difference for a short period of time.  In general:

Inflow => Outflow 

for a satisfactory setup.  The reservoir evens out the pressure
fluctuations, and does allow for some peak flow events.

>- then it's not so good a buy.

You do not have to put the tank directly attached to the compressor.
The additional reservoir can be anywhere in the plumbing system.
There is even some benefit to placing a reservoir near the usage point
to even out pressure drops from piping flow losses.  

The bottom line is that if the compressor matches your outflow needs,
then it will work for you.  Worry about the tank if pressure
fluctuations or short term high peak flows are a problem. 

J. M. Stuart

Engineer / Inventor / Patentee