Ok guys so I need some help. I have an aircompresser that is running
my waste oil burner. The burner needs very little air pressure. I
want to lower the start up pressure so that the compresser runs
longer when it is on and stays off longer. Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

Thanks,
Zach

Check with your local refrigeration tech. He has access to all kinds of
adjustable pressure switches. Any voltage. Most refrig controls turn on with
a high pressure and shut off with a low pressure, but he can get one that is
the opposite.
*********************************
Ok guys so I need some help. I have an aircompresser that is running
my waste oil burner. The burner needs very little air pressure. I
want to lower the start up pressure so that the compresser runs
longer when it is on and stays off longer. Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

Thanks,
Zach



--
Posted via a free Usenet account from http://www.teranews.com

Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

http://omega.com/

On Dec 20, 12:33 am, wrote:
Ok guys so I need some help. I have an aircompresser that is running
my waste oil burner. The burner needs very little air pressure. I
want to lower the start up pressure so that the compresser runs
longer when it is on and stays off longer. Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

Thanks,
Zach

Zach

My Craftsman compressor has an adjustable pressure switch, 2 springs
with adjusters if I remember right. There is significant interaction
between the adjustments and maybe not the wide off/on range you are
looking for.

What are you doing with the waste oil burner? I like to see pictures
or drawings. I am thinking about building an oil burner for a
crucible furnace.

Carl Boyd

On Wed, 19 Dec 2007 21:33:59 -0800 (PST),
wrote:

Ok guys so I need some help. I have an aircompresser that is running
my waste oil burner. The burner needs very little air pressure. I
want to lower the start up pressure so that the compresser runs
longer when it is on and stays off longer. Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

Thanks,
Zach


Hey Zach,

That's a substantial amount of differential. What about just using a
2nd switch, say like one used for water pressure, and that way you can
get the differential you want.

On Wed, 19 Dec 2007 21:33:59 -0800 (PST),
wrote:

Ok guys so I need some help. I have an aircompresser that is running
my waste oil burner. The burner needs very little air pressure. I
want to lower the start up pressure so that the compresser runs
longer when it is on and stays off longer. Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

Thanks,
Zach

Two standard pressure switches, a little bit of relay logic - The
low pressure switch pulls up a "Run" relay that locks even after the
low-pressure switch has opened, and the compressor runs until the
stock high-pressure switch is satisfied and turns it off.

You will need a small DPDT relay for the latching start, and a plain
power contactor to start the motor. Or a motor contactor with an
auxiliary SPDT contacts.

A full-on motor starter is better - first it has the aux. latching
contacts built in for using "Start" and "Stop" buttons, so you could
wire it all by itself, no external logic or second relay. (Follow the
directions on the inside of the motor starter cover.) And you have
overload heaters in case of a locked rotor no-start - make sure you
know the motor full-load amps to select the right overload heaters.

And do NOT use the bleeder style unloader valve built into the stock
high-pressure switch with this setup - if you lose power and try to
start the motor on a high head pressure load, it might not start. Or
the pressure could build up on the compressor output side if you have
a leaky tank check valve - the high pressure switch's built-in bleeder
valve closed at 120 PSI, and has been sitting there closed till the 35
PSI start switch finally kicked in...

Get an 1/8" NO solenoid valve (closes on power), hook the coil
across the motor leads, and make it the unloader valve. Motor stops,
valve unloads.

-- Bruce --

Basic thermodynamics says it is not efficient to run the compressor to
high pressure and then bleed it down to low pressure. Set the stock
pressure switch to the maximum differential (one of the screws), then
lower the max pressure to whatever is required to make the cut in
pressure correct (This is logically backwards, but that's the way the
switches work) This will mean the compressor runs more often but won't
work as hard when it does.

wrote:
Ok guys so I need some help. I have an aircompresser that is running
my waste oil burner. The burner needs very little air pressure. I
want to lower the start up pressure so that the compresser runs
longer when it is on and stays off longer. Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

Thanks,
Zach

On Fri, 21 Dec 2007 12:37:00 -0600, RoyJ
wrote:
wrote:

Ok guys so I need some help. I have an aircompresser that is running
my waste oil burner. The burner needs very little air pressure. I
want to lower the start up pressure so that the compresser runs
longer when it is on and stays off longer. Does anyone know who makes
a pressure switch that is adjustable. Like maybe 35psi lower to 135
upper?

Basic thermodynamics says it is not efficient to run the compressor to
high pressure and then bleed it down to low pressure. Set the stock
pressure switch to the maximum differential (one of the screws), then
lower the max pressure to whatever is required to make the cut in
pressure correct (This is logically backwards, but that's the way the
switches work) This will mean the compressor runs more often but won't
work as hard when it does.

Your logic is sound, but there is another thing to consider - an
electric motor in severe duty (as on an air compressor) is usually
only rated for four to five starts an hour maximum. Even if it's
lightly loaded, as it would be on a 110-135 PSI single-stage
compressor derated to running at 35-50 PSI duty.

When you start an electric motor it's drawing "locked rotor" current
for a half second till it gets up to speed, and that builds up a lot
of heat in the interior of the motor windings. The heat only gets a
chance to start dissipating when the motor gets up to speed and the
cooling fan gets moving. Multiple short cycles per hour will quickly
burn up the motor - it's better to let it run than to have it stop for
three minutes and start again.

If he was going to do this the /right/ way, that really is the
proper job for a small diaphragm or "wobble piston" oilless air
compressor sized to the pressure needs and air consumption of the
babbington burner - say 1/4 or 1/6 HP. Have it start when the oil
burner lights off, and run continuously while the burner is lit. And
when it wears out they are rebuildable or disposable.

Another solution is a continuous-run compressor that leaves the
electric motor running and unload the compressor head for the short
lulls between calls for air. But that makes more sense on a 25-HP or
bigger compressor supplying a large plant than a 2-HP compressor at a
residence.

But if he doesn't want to do that, the large differential is second
best. Then the compressor only has to cycle on once or twice an hour.

-- Bruce --

On Fri, 21 Dec 2007 12:37:00 -0600, RoyJ wrote:
Basic thermodynamics says it is not efficient to run the compressor to
high pressure and then bleed it down to low pressure. Set the stock
pressure switch to the maximum differential (one of the screws), then
lower the max pressure to whatever is required to make the cut in
pressure correct (This is logically backwards, but that's the way the
switches work) This will mean the compressor runs more often but won't
work as hard when it does.

Agreed, that sounds like the winning approach.

In addition, you might consider adding air storage. That way it does
run longer when it runs, and runs less often.

Both of those are pretty simple, standard ways to approach the original
goal.

sdb
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