So? You said you only need it for occasional "high flow" jobs. If you
need it to fill faster, install a manual valve to override the restrictor
when you absolutely have to, and let the pump work longer in one session.
(the total pump time will _always_ be the same per cubic foot of tank
capacity, so you save nothing in pump run time, either way. It either
runs in 'bursts' until it's filled the big tank, or it runs
continuously...total time is the same).
Again... remember that you're only drawing from that big tank when the
small one can't provide the flow you need.
Let me revise my comment a little.
You're a math guy. How will the big tank _ever_ fill quickly, and still
not prevent you from getting full pressure quickly in the small tank?
Opening a 'pass-over' valve to the big tank once the small one is full
won't do it! It'll drop the system down to system peak divided by the
ratio of tank volumes the INSTANT you open it (well, within seconds). So
the pump will come back on, and now run an intolerable length of time
before you have enough pressure to work. You can't have 'quick' and
'full pressure' in the same formula.
Pump capacity is the limit; always.
If your pump cuts in at 90, then all you've done is complicate the system
without improving the performance. The INSTANT your system hits 120,
it'll dump _all_ your main tank capacity into the reserve until the
pressure drops to 90 -- then the electric valve turns off and the pump
starts to run again... it will not improve the length of time it takes to
get the reserve up to pressure. That's dependent entirely on pump
capacity. It matters not how you fill it, it will always take the same
length of time.
Your method will NOT improve run time, or the time to reach "usable" air
pressure in the main tank, except for a slight (say 10%) time. But it
will increase the complexity and maintenance issues over a simpler,
Ig... for any given solution that will work, simpler and less expensive
is always better.
On 2013-12-07, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:
Actually, if you think about it, the compressor will run continuously
from the time the pressure hits 120, until such time the reserve tank
is filled. All the while, the system pressure will never drop below
During filling, no energy will be lost, unlike with restricted valves.
probably not. The 90-120 psi stuff is just a distraction from the real
problem. you don't want to fill the large tank when there's a load on your
compressor from tools. Pressure on the system doesn't truly indicate if
you have a load or not.
I don't deal with air systems, maybe somebody can answer this-
do they make simple flow guages or sensors for compressed air systems?
If so connect both tanks with a check valves in a Y, allowing flow out to
your load, but no flow between tanks. The connection to each tank from the
compressor is with a solenoid valve in the same Y configuration. The only
states are compressor connected to no tank, connected to the small tank,
connected to the large tank or connected to both tanks.
back to the flow detector-
When you detect a load on your system, disconnect the large tank from the
compressor. Only the small tank is connected to the compressor. It will
fill quickly so nobody is standing around.
If there is no, or low tool load, disconnect the small tank from the
compressor, and connect the compressor to the large tank. The air supply
to your load will be from the tank with the highest pressure, which is the
small one. Immediate usage needs are met.
When the pressure there (small tank) drops too much, you start the
compressor and disconnect the large tank.
Add a pressure sensor to the large tank. Once it hits minimum acceptable
pressure (90 in your case) leave both valves from the compressor to both
tanks open. You're now using the capacity of both tanks and the fill of
the large tank never interrupted with your immediate use requirements.
You need a little logic to run this, but it's nothing beyond a couple
With a little additional programming, the pressure transducer information
could be used to get a little more run time at pressure. For example you
could measure the rate of pressure change when the compressor is running but
no air is being used. The rate of change for the compressor can be compared
to current rate of change of air usage. If air is being used as fast as or
faster than what the compressor can keep up, you can turn in on before 90
PSI to give you more run time at pressure than you'd get waiting until 90
PSI to turn it on. Not sure that it would help you much but set points that
vary with demand can give you more air.
About the run time, let me see if I can explain it better. For example,
let's say your sandblaster needs at least "X" psi to operate correctly. Now
if your sand blaster drains your tanks at 15 PSI per minute, and your
compressor adds 10 PSI per minute, then with the compressor on, you have a
loss of 5 PSI per minute. So if you could detect usage rate > compressor
rate, and turn on the compressor at 120 PSI instead of 90 PSI, you get 6
minutes of usage at a loss of 5 PSI per minute, from 120 to 90 PSI. With
the compressor off, you get 2 minutes from 120 to 90 PSI.
I understand at this point the computer idea sounds too complicated /
expensive but that's kind of like your EMC experience. Sounded like too
much unfamiliar territory but you took it step by step, solved one problem
at a time, and ended up with a system that you can repair without high $$
parts and labor. And you added a 4th axis + knee?, that may not have even
been an option with the original control.
If anything like this ever seemed practical, options include a micro PLC
with analog input or something like an Arduino board, $30, has analog
inputs, free software, screw terminal add on for around $8. The 5V output
from the microcontroller can be used on AC or DC solid state relays to
control valves and/or magnetic contactors. So it's actually nothing like
using a PC and trying to interface to a compressor. Or perhaps some of you
scrap deals could have a controller in them that could be reprogrammed for
I considered similarly overengineering a computerized draft regulator
for my woodstove, with inputs from firebox, stack and outdoor air
temperature and the draft vacuum, all of which I was monitoring. It
would be fun and a considerable accomplishment to tune it properly.
I've designed relay-ladder controls for industrial production test and
burn-in stations and wired/programmed simulations of the rest of the
system for circuit board test and calibration fixtures.
For the woodstove I decided instead to add a remote thermocouple
temperature display above this computer's monitor, so I know at a
glance to go down and attend to it when it has reached operating
temperature or needs more wood. A second channel tells me when a pot
on the stove is nearing boil.
When I sandblast with an inadequate compressor I hang a large pressure
gauge on the wall nearby and attack a new area with hammer and chisel
until the pressure recovers enough to continue.
I've learned to be cautious of designing complex things for other
people's use that only the designer can fix.
I wired an Allen Bradley PLC 5 to a Brinkman Gourmet Electric Smoker. Had a
PanelView 550 for operator interface. A RTD probe for the meat and another
for the temperature inside the smoker. The meat set point temperature
ramped up over 12 hours as the smoker temperature was kept within limits.
After the temperature was reached, it was held for a period of time to allow
it to even out, then brought down to a set point of 140 degrees for "keep
warm". It worked great but was a pain to drag out & set up then put back
up. I need to mount the controller in a box and use plugs for the
temperature probes and power. It was done for fun but made pretty good BBQ,
need an automatic smoke wood feeder!
Next step I could use some actuators for the air inlets and control my Weber
Smokey Mountain smoker!
PLC 5's are a bit old but their cards are cheap since the 1771 racks date
back to PLC 2's. The downside is the programming software but I have it on
my work laptop.
True, if you make a mistake with the program, you may never find out!
However, about everything that can be sensed with electronic sensors can be
fed into a controller and acted upon or at least sound an alarm. So, on a
wood stove you could monitor temperatures, carbon monoxide, or any other
relevant conditions that you might want to monitor on a wood stove.
Controls checking and acting on conditions hundreds of times per second can
catch and correct a problem better than a person can.
I used to attempt to fly R/C helicopters before Gyro's were common to assist
tail rotor control, probably averaged 1/4 tank of fuel between crashes.
After purchase of a cheap mechanical gyro, next crash was around 70 full
tanks of fuel later. The crash after 70 tanks of fuel was due to getting it
too far away and losing orientation, not a control or gyro related problem.
I share Iggy's concern enough that I don't run the stove when I'm
away. In midwinter I came home from work to a 50F house, the setting
of the electric backup.
The control I was considering would have closed the air inlet on the
door as the stove came up to temperature. I didn't add it because I
don't want any possible interference if the fire runs away and I need
to shut it down.
After Thanksgiving I let the house cool to measure the rate vs
outdoor temperature. At 2AM on Saturday the smoke alarm blasted me out
of bed, to the smell of something electrical that had overheated. I
rushed around checking all the electronics, found nothing warm,
rechecked them twice anyway. Then I noticed that the smell was
strongest near the hallway radiator, which hadn't been disassembled
and vacuumed out in a long time. I had forgotten about the backup
setting. The radiator had turned on, and the alarm and hot plastic
smell were from rug fibers in it.
I woke up to some fun this morning. -=No water=- The pump pressure
is up but the lines are frozen. I put a heater in the pump house (the
light had burned out, allowing the freeze?) an hour ago but no joy
yet. I'll put it in the crawlspace in a few minutes and see if that
does it. <sigh>
It has been 10 or 11F here two days in a row. The lowest I've seen
here before is 17F, and my outside line burst 8 years ago. I have
insulated the exterior pipes and shut them off for the winter now, so
this is the first problem I've had, and the first time losing water.
There's a shutoff valve for each inside and outside lines.
I bought a 200W Lasko personal heater for $12 in WalMart to see if it
can keep my water meter above freezing when I'm away without running
up an excessive electric bill. Right now it's defrosting dinner. It
could be wired through an electric heat wall thermostat as a backup to
the light bulb that distributes heat differently, like downwards or
through a conduit.
For the light bulb:
Wow, aren't those little cuties? That's much better for ladies' feet
under the desk than a 1,500W energy sucker. I wish I'd seen that
earlier today when I visited Wally World for my prescription, which
just left the $4/mo list and cost me $15.68 instead. Big Pharma
ended their price deal with Wally and bumped prices a wee bit!
The Lasko MyHeats are $18.62 today.
Dinner, eh? <heh heh heh>
That's a thought.
I've been wanting to replumb in PEX and insulate the crap out of it
when done, but the ongoing recession took care of that for me. Red
Beacon (thru Home Depot) is bringing more work to me during the wet
season than ever before, so I may be able to afford that next year.
Hmm, I may do that some day...
3:30pm update: Shit, still frozen shut. I had warmed the pump house
for over an hour, then put the heater aimed at the pipe in the
crawlspace for about 4 hours, but it's still frozen. Temps had risen
to 31F for awhile, but are back to 28F now and dropping. <sigh>
Rain is due Weds, so I hope to have water again by then.
I saw no indication of burst pipes during my quick foray under the
house. The visqueen was dry to the end. I'm keeping my fingers
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