Don:
Required LBC content in last paragraph.
<<<snip>>>
If I have the air compressor in an unheated garage will
there be a
problem with starting it in cold temperatures: 20F?
<<<snip>>>
Possibly. When mentioned the belt slipping that was
experience talking. The approx. 3 HP compressor (5.8 CFM at
90 PSI) tried to start but couldn't. I just happened to be
in the shop at the time. My shop is heated most of the
time, but the heat had been off for awhile when this
happened. The problem may have been moisture in the system
which had frozen. I even pulled the head trying to figure
out why the compressor didn't want to start up. Of couse by
then I had the heat on and couldn't find anything wrong.
After that the compressor didn't seem to have quite the same
output.
<<<snip>>>
Should I leave it depressurized so starting it in cold
weather will be easier?
<<<snip>>>
Most larger compressors have an unloader. On many of them
this is a small air tube running from the pressure switch
back to the cylinder head. When the pressure switch shuts
off the power to the motor, it also opens a small valve
which releases the air pressure in the air line going from
the compressor to the tank. There is a check valve when the
air line from the compressor goes into the air tank. Thus
when the compressor starts, it starts under no pressure. On
larger compressors this is a must as the electric motor
doesn't have enough torque on startup to turn the compressor
over under load. The unloader also relieves the reed valves
in the compressors cylinder head from having to act as a one
way foot valve.
That also brings up another important item. Don't pull the
plug on a compressor while it's still running. Doing so
does not allow the unloader to drop the air pressure in the
lines. Then the compressor can't start up against the
pressure in the line. The old Sears unit I mentioned about
had a lever which could manualy unload the compressor if
necessary. The new 11.2 CFM Sanborn unit I am now using
doesn't have the unloader lever. That Sears unit is now
chugging merrily away in my brother's garage. (He bought it
originally, I inherited it because he owed me $$$, I finally
got some of the $$$.)
<<<snip>>>
why would I care about dual stage?
<<<Snip>>>
Usually higher PSI. My single stage is about max in size
and PSI: 120. Two stages are quite often 150 PSI. The
higher PSI is needed for 1/2 inch impacts when trying to
remove lug nuts. The 120 PSI of my unit will barely do it
if the nuts were properly torqued and not just ramed on with
a tire shop air wrench.
<<<snip>>>
I'm getting the CFM I need, at the cost I want to pay, then
why do I care about motor size?
<<<snip>>>
You're right. The CFM is the critical number. Marketers
have played around with the HP ratings of electric motors.
That Sears unit I was describing had a 1 HP rated motor, 17
amps at 120V I think and it said so on the tank label. To
get the same delivery rate today, you would find the
compressors motor now rated at 3-4 HP.
I think that electric motors used to be HP rated while
running. Now they are rated under startup when the extra
juice from the capacitors is used. They cannot run
continuously at the rated HP as they will burn up. It's
like the starter in most cars. They're 6 volt being
opperated on 12 volts. Works great as long as you don't
crank very long.
Blake
Blake
/// or try http://www.team.net/cgi-bin/majorcool
/// Archives at http://www.team.net/archive
|