I have just got my new 100 Litre (3hp) upright compressor and notice
that its only charging to 7bar.

I wondered if the gauge was inaccurate, but its got 2 and both read
almost exactly the same.. As I final test, I have a engine compression
tester which I connect and indeed its at around 7 bar.

Is there any reason why I should not adjust the 'cut off' so that it
fills to 8bar? If it has 8 bar in the tank as opposed to 7, then I
assume am going to get more air out (100 litres more), but its
obviously going to take longer to charge and will put extra pressure on
the tank and fittings.

Has it been set to 7 intentionally, or is it normal to 'fine tune' it
during its first few used?

Any info would be appreciated

Jon

On Tue, 07 Feb 2006 09:02:32 -0800, jon.p.weaver wrote:

I have just got my new 100 Litre (3hp) upright compressor and notice
that its only charging to 7bar.

I wondered if the gauge was inaccurate, but its got 2 and both read
almost exactly the same.. As I final test, I have a engine compression
tester which I connect and indeed its at around 7 bar.

Is there any reason why I should not adjust the 'cut off' so that it
fills to 8bar? If it has 8 bar in the tank as opposed to 7, then I
assume am going to get more air out (100 litres more), but its
obviously going to take longer to charge and will put extra pressure on
the tank and fittings.

Has it been set to 7 intentionally, or is it normal to 'fine tune' it
during its first few used?

Any info would be appreciated

Jon

7 bar is 100 PSI, 8 bar is 120. I wouldn't think that would hurt
anything.

wrote in message
oups.com...
I have just got my new 100 Litre (3hp) upright compressor and notice
that its only charging to 7bar.

I wondered if the gauge was inaccurate, but its got 2 and both read
almost exactly the same.. As I final test, I have a engine compression
tester which I connect and indeed its at around 7 bar.

Is there any reason why I should not adjust the 'cut off' so that it
fills to 8bar? If it has 8 bar in the tank as opposed to 7, then I
assume am going to get more air out (100 litres more), but its
obviously going to take longer to charge and will put extra pressure on
the tank and fittings.

Has it been set to 7 intentionally, or is it normal to 'fine tune' it
during its first few used?

Any info would be appreciated

Jon


Most likely your compressor was set at a cut off that is most efficient for
the design of your compressor. If I remember correctly, 1 bar is just over
14 psi. That puts your compressor at ~100 psi. That's normal for a home use
compressor. Raising the pressure to ~114 psi PROBABLY isn't dangerous, but
would add extra strain to your motor and compressor without giving you much
benefit. I certainly wouldn't try to raise the pressure any higher.
Compressed air can be very dangerous.

wrote: (clip) Has it been set to 7
intentionally, or is it normal to 'fine tune' it during its first few used?
Any info would be appreciated.
^^^^^^^^^^^^^^^^
Certainly, besides the pressure switch (now set to 7 bar) it must have a
pressure relief valve. As long as that is working properly, I don't think
there is any danger.

8 bar will give you a little bit more air capacity, but the motor will have
to run longer and work harder to reach the new set point. Since the
volumetric efficiency of the pump drops as the back pressure is raised, you
could start to approach a situation where the pump has to work a lot to give
you a little.

wrote in message
oups.com...
I have just got my new 100 Litre (3hp) upright compressor and notice
that its only charging to 7bar.

I wondered if the gauge was inaccurate, but its got 2 and both read
almost exactly the same.. As I final test, I have a engine
compression
tester which I connect and indeed its at around 7 bar.

Is there any reason why I should not adjust the 'cut off' so that it
fills to 8bar? If it has 8 bar in the tank as opposed to 7, then I
assume am going to get more air out (100 litres more), but its
obviously going to take longer to charge and will put extra pressure
on
the tank and fittings.

Has it been set to 7 intentionally, or is it normal to 'fine tune'
it
during its first few used?

Any info would be appreciated

Jon


Jon,

If it's been sold in the UK it should bear a test plate stating the
test pressure and the safe working pressure - or just conceiveable be
provided with a certificate - though unlikely if sold into the 'hobby'
market.

AWEM

"Ignoramus11278" wrote in message
...
First, find out what your compressor is rated for. Second, for any
given pressure that is demanded by your actual tools that you plug in,
the most efficient compressor setting would be pressure just above
that. Increasing pressure beyond that only wastes energy.

really? when i'm blasting at 40psi, i can run a long time given a large tank
between times the motor actually kicks on. if it was producing 45 psi in the
tank, the motor would be running all the time.

regards,
charlie
http://glassartists.org/chaniarts

On Tue, 7 Feb 2006 11:15:11 -0700, the renowned "Charles Spitzer"
wrote:


"Ignoramus11278" wrote in message
...
First, find out what your compressor is rated for. Second, for any
given pressure that is demanded by your actual tools that you plug in,
the most efficient compressor setting would be pressure just above
that. Increasing pressure beyond that only wastes energy.

really? when i'm blasting at 40psi, i can run a long time given a large tank
between times the motor actually kicks on. if it was producing 45 psi in the
tank, the motor would be running all the time.

Aside from the differential, what's the formula for energy stored in a
tank vs pressure? Proportional to the square of pressure maybe?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

really? when i'm blasting at 40psi, i can run a long time given a large
tank
between times the motor actually kicks on. if it was producing 45 psi in
the
tank, the motor would be running all the time.

regards,
charlie
http://glassartists.org/chaniarts



Yep, really. Have you ever noticed that many compressors give 2 different
cfm ratings? One will be at a low pressure, and one will be at a higher
pressure. The higher pressure always has a lower CFM.

Of course an air compressor motor uses a lot of electricity at start up, and
less once it's up to speed, so that would have to be figured into the
equation.


Dave, who has a 3000 psi compressor, and a booster for when that's not
enough.

In article .com,
wrote:

Is there any reason why I should not adjust the 'cut off' so that it
fills to 8bar? If it has 8 bar in the tank as opposed to 7, then I
assume am going to get more air out (100 litres more), but its
obviously going to take longer to charge and will put extra pressure on
the tank and fittings.

All depends upon the parts, and the design working pressure of each
part. 12 bar (175 PSI) is not uncommon (usually with regulators on the
outlets to drop to 6-7 bar (90-100 PSI) for working), but only if the
compressor, tanks and all accessories are designed to take that - and
your more sensible/cautious practitioner will prefer a system where all
parts (perhaps excepting the compressor) are rated for a good deal more
(say 20 bar/300 PSI) for some safety factor, with an over-pressure
relief valve set above the working pressure and below the max safe rated
pressure.

--
Cats, coffee, chocolate...vices to live by

It sounds to me that you are getting pressure and volume mixed up. You
could have a compressor that puts out 500 cubic feet a min. but not the
power to compress more than 50psi. and you can have a compressor that puts
out 300 # of pressure but just a .25 cubic feet a min. like those little
compressors that run off your car battery for flats.
Dick

--
Richard H. Neighbors
Building and repairing fine billiard cues for real pool players at
affordable prices.
Over 35 years exp. Located in Cincinnati OH
ph.# 513 233-7499
e-mail
web site http://www.dickiecues.com
"Ignoramus11278" wrote in message
...
On Tue, 07 Feb 2006 13:37:53 -0500, Spehro Pefhany
wrote:
On Tue, 7 Feb 2006 11:15:11 -0700, the renowned "Charles Spitzer"
wrote:


"Ignoramus11278" wrote in message
...
First, find out what your compressor is rated for. Second, for any
given pressure that is demanded by your actual tools that you plug in,
the most efficient compressor setting would be pressure just above
that. Increasing pressure beyond that only wastes energy.

really? when i'm blasting at 40psi, i can run a long time given a large
tank
between times the motor actually kicks on. if it was producing 45 psi in
the
tank, the motor would be running all the time.

If your compressor needed to run all the time to produce 40 PSI at
your demand rate, you could not go above 40 PSI. Since you can go
above 40 PSI, your motor would run intermittently.


Aside from the differential, what's the formula for energy stored in a
tank vs pressure? Proportional to the square of pressure maybe?

I would expect it to be proportional to cube of pressure, since
temperature of compressed air rises proportional to compression. That
extra heat is fully wasted, unlike the (potential) mechanical energy
of compressed air.

i

On 7 Feb 2006 09:02:32 -0800, wrote:

I have just got my new 100 Litre (3hp) upright compressor and notice
that its only charging to 7bar.

I wondered if the gauge was inaccurate, but its got 2 and both read
almost exactly the same.. As I final test, I have a engine compression
tester which I connect and indeed its at around 7 bar.

Is there any reason why I should not adjust the 'cut off' so that it
fills to 8bar? If it has 8 bar in the tank as opposed to 7, then I
assume am going to get more air out (100 litres more), but its
obviously going to take longer to charge and will put extra pressure on
the tank and fittings.

Has it been set to 7 intentionally, or is it normal to 'fine tune' it
during its first few used?

If this is a single-stage one cylinder compressor, 7 BAR / ~100 PSI
is a reasonable setting and will run most any tool you have. You can
go slightly higher IF the pump and motor combination can handle the
extra load, and the tank and plumbing are rated for it.

The manufacturer deliberately sets the pressure switch in the
factory at a "safe" level slightly lower than the maximum the pump and
motor assembly can attain, so they don't have to deal with failures
brought on by excessive running time (as it labors to get that last
pound) or motors overheating.

All pumps have a maximum pressure where you don't get any useful
output, and for a small single stage, that's about it. If the motor
doesn't overload and stall, the pump output drops off to nothing.

And they set the switch with a reasonable differential point of
between 15 - 30 PSI (1 - 2 BAR) so it isn't starting and stopping
constantly - you can damage the motor by starting it more than 6 to 10
times an hour, the start capacitor or winding can overheat.

If you need higher pressures on a regular basis, you have to go to a
two-stage pump. They are good for 150 - 175 PSI.

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.

Call the manufacturer and ask them. I did so with a similar situation
many years ago. The engineer that I finally got connected to asked for
my telephone number and called me back to make certain that I was who I
said I was, not some government official!
He reminded me that the tank on my compressor was not ASME
certified. But he then told me that it was fine to turn it up. I did
that in about 1980 and have been using it that way ever since.
1 HP 2 cylinder compressor with 12 gallon tank.
Original value (USA) 90 psi
Reset to 125 psi.
Pete Stanaitis


wrote:
I have just got my new 100 Litre (3hp) upright compressor and notice
that its only charging to 7bar.

I wondered if the gauge was inaccurate, but its got 2 and both read
almost exactly the same.. As I final test, I have a engine compression
tester which I connect and indeed its at around 7 bar.

Is there any reason why I should not adjust the 'cut off' so that it
fills to 8bar? If it has 8 bar in the tank as opposed to 7, then I
assume am going to get more air out (100 litres more), but its
obviously going to take longer to charge and will put extra pressure on
the tank and fittings.

Has it been set to 7 intentionally, or is it normal to 'fine tune' it
during its first few used?

Any info would be appreciated

Jon

On Tue, 07 Feb 2006 17:51:45 GMT, Ignoramus11278
wrote:

the most efficient compressor setting would be pressure just above
that. Increasing pressure beyond that only wastes energy.

No, increasing tank pressure as much as possible (subject to the
compressor's capabilities and the tank rating) will increase efficiency.
This will be most noticeable if you use a "thirsty" tool in short
bursts.

On Tue, 07 Feb 2006 13:37:53 -0500, Spehro Pefhany
wrote:

Aside from the differential, what's the formula for energy stored in a
tank vs pressure? Proportional to the square of pressure maybe?

Yes, square - ignoring losses.