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Scatterplot
07-24-2007, 03:52 PM
I've got an application that needs to flow a gallon of a liquid and then shut off. The metering part of it is mechanical, and needs a small amount of reverse flowing through a pump to seal off the chamber. I'm filling gallon jugs with this. I saw this pump: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=1479
and it looks ideal, as it'll take about 14-15 seconds to fill a 1-gallon container. I'd like it to be a little bit faster but that's not what this thread is about.

Anyways, the backpressure thing is what I can't get. The liquid doesn't need to be sucked through the tube, but I do need about 2 inches of 1" tubing's worth of liquid to be able to go backwards through that pump. I looked at the manual and it might be able to let the liquid flow backwards when shut off, but it'll be more of a trickle- this needs to happen pretty quick. I was thinking I could reverse the motor for about .25-.5 seconds when it hit me, duh, it's an AC motor. Is there anything short of rewinding the thing that will let me make this stuff flow backwards for a teeny amount of time? The only electronics I will be using would be a small 555 timer or two, I could use microcontrollers if I had to but it would get tedious, and I'm going for easy here.

pcarpenter
07-24-2007, 03:59 PM
Does it have to be *reverse* flow? if not, you could tap the outlet side of the pump and divert a small amount (using a needle valve to control the amount) to the chamber you mentioned. I am guessing this might mean that you would have to drill and tap the chamber for a fitting for this "feedback loop".

Just a thought.

Paul

sidegrinder
07-24-2007, 04:01 PM
I didn't look at the link to the pump, but wouldn't it work to have the pump at a lower level than the fill pipeline? Then when the pump turns off you would have a small "back-siphoning" effect. Just trying for a simple solution, I'm sure one of our techno-wizards will be around shortly ;) Sidegrinder

Evan
07-24-2007, 04:02 PM
One way valve going to the container. After the pump and before the valve a short vertical standpipe closed at the top with some air inside (better is an air bladder, maybe a trojan? :D ). Size the pipe to hold the correct quantity. Pressure developed while pumping will return the liquid when the pump stops.

Note: Valve needs a spring that only opens it under full pump pressure.

pcarpenter
07-24-2007, 04:03 PM
I re-read your post and the original response I typed and then threw out seems like it just might be applicable. If you have 2" of 1" tubing between the inlet to the pump and the supply of liquid, I would think that it would fall backward immediately under the force of gravity...at 9 meters/second (roughly the acceleration due to gravity) which is pretty darned quick.

I think that if you had *lots* of outlet hose, then you might find the drainback to be much slower...but not in the case above.

paul

Weston Bye
07-24-2007, 04:13 PM
The pump appears to be an impeller-type pump so should provide very little restriction to reverse flow when not running.

If you placed a tee on the output of the pump and check valve on one side of the tee and a small accumulator on the other, the spring that holds the check valve closed would present a little back pressure - enough to fill the accumulator. When you shut off the pump, the pressure would drop until the spring closes the check valve. Any remaining liquid in the acumulator would flow back through the pump.

The check valve with the spring is acting like a pressure regulator or pressure relief, and you might have to fiddle with the spring force a little.

Edit: Evan beat me to it. And everyone else suggested a hydraulic solution. Now if the pump were positive displacement...

cadwiz
07-24-2007, 08:42 PM
Evan's got it. The check valve/vertical standpipe works great for this application, I use it all the time at work for metering small flows. Also very effectively dampens out pulse effects from diaphragm pumps, much like resistance/capacitance elements in an electrical circuit.

Cadwiz

BigBoy1
07-25-2007, 11:01 AM
I'm still not quite sure what you are doing but could you use a mechanical solution? If you want to fill a gallon container and them shut the pump off, what about having the pump fill a gallon containter that is on a pivoting arm? The couterweight of the arm would be an identical container with slightly less than a gallon of fluid in it. When the container being filled reached a gallon, the arm would pivot and trip the shut off switch for the pump.

If a flow back is required for the pump, maybe set the container at a higher level than the pump and when the swithed is tripped, the fluid in the line would them flow back into or cause a back pressure on the pump.


Bill

Scatterplot
07-25-2007, 12:56 PM
It's not a back pressure on the Pump I need, I need a vacuum on the homemade valve thing. So far carpenter has had the closest idea- the only problem would be it venting somewhat while the pump ran, but that would be OK.

I'll try to whip up a CAD model after lunch today, it's a really simple design.

Backwards flowing isn't a problem if done by gravity- I just needed a VERY small amount of somewhat quick suction operating on the valve- the "quick" part is what gets me. Gravity-assist or pressure assist will be too slow, I think. I haven't looked at the pump in person so I can't be sure though.

camdigger
07-25-2007, 01:24 PM
Scatterplot

FWIW, reversing the rotation of the pump shown will not reverse the flow. That is a centrifical or vane pump and pressurizes the water it pumps by slinging it from the suction port in the center of the impeller against the casing around the impeller. Reversing rotation will make it less efficient, but not reverse the flow.

A gear pump will reverse flow with direction, most piston pumps will not, diaphram pumps will not, plunger pumps won't either.

Rather than starting and stopping the pump, you could pump into a pressurized chamber and open and close a filler valve with a solenoid. A timer would be activated long enough to flow a gallon into the jugs.

Centrifical pumps are sold complete with pressure switches for water well and water sytem installations for rural properties with relatively shallow wells. +/- 280$CDN complete as of last week when I replaced mine.
Cam

Scatterplot
07-25-2007, 01:32 PM
Scatterplot

FWIW, reversing the rotation of the pump shown will not reverse the flow. That is a centrifical or vane pump and pressurizes the water it pumps by slinging it from the suction port in the center of the impeller against the casing around the impeller. Reversing rotation will make it less efficient, but not reverse the flow.

A gear pump will reverse flow with direction, most piston pumps will not, diaphram pumps will not, plunger pumps won't either.

Rather than starting and stopping the pump, you could pump into a pressurized chamber and open and close a filler valve with a solenoid. A timer would be activated long enough to flow a gallon into the jugs.

Centrifical pumps are sold complete with pressure switches for water well and water sytem installations for rural properties with relatively shallow wells. +/- 280$CDN complete as of last week when I replaced mine.
Cam



Hmm... that does not bode well. I was hoping to get maybe like 1 rotation or something out of it- it really doesn't have to be much at all. I'll get that CAD thing done real fast, then maybe someone smarter than me will show me why it'll kill me.

Magic9r
07-25-2007, 03:05 PM
You could use a pair of pumps with check valves, connected in parallel with one to pump in & one to pump out, you could keep your system and control really simple and get exactly the function you have described, if the pumps allow little backflow you could dispense with the valves,
Regards,
Nick

Swarf&Sparks
07-25-2007, 03:21 PM
Peristaltic pump allows precise metering and is easily built by the HSM

Scatterplot
07-25-2007, 03:43 PM
I like that idea, I hadn't thought about that. Where might one find more information on these? I've seen them before and know generally about them but I wouldn't know how to properly design one (for example, what hose do I use?) I'd like to look into that some more, it actually sounds better than an impellor type.

Anyways...
http://www.imagehosting.com/out.php/i954490_ValvePic.jpg

Here's my valve design. The way it would work is that the right side would be connected to a pump source, the middle connected to a reservior, and the left being the outlet. This is all PVC- the middle is a tee with the inner stops turned off, and a pipe with a hole in the side going through the middle. This presents a constant-diameter tube with an outlet. The thing in the middle is "the plunger" for lack of a better term. The image technically doesn't show the plunger in the right spot, nor any holding mechanism, but they would be there. Anyways. The spring, when fully extended, would hold the plunger forward, connecting the center and the exit. When the pump comes on, the plunger slides forward and seals off the front, while allowing the fluid to flow into the middle chamber. The middle chamber is actually what has been described, an accumulator of sorts. Just a sealed, approximately 1 gallon container (more for the air.) Some type of detection system would sense when the container is full (float and magnet, pressure, etc.- just something volumetric as this is a universal type for fluids of different densities, thus ruling out weight- although that could simply be calibrated, it is beyond the scope of this project). Anyways, when the sensor detects that one gallon has been metered to the central chamber, the pump shuts off.

Given enough time the spring will move the plunger back into position on the other side of the gap, and let the measured amount flow through the middle and left holes, thus dispensing a gallon. The problem is that with a fairly viscous liquid, this could take a while- on the order of seconds, which is a long time when you're filling about a hundred gallon-size containers. The reason for reverse-suction is so the plunger slides back and switches the flow quickly- there isn't much need for a high flow, just a *teeny* bit really fast.


I know there are some problems with the overall design, and I'm not sure how the timing would be (would it just be quicker to do by hand, etc.) but what do you guys think?

BTW, I'm shooting for simplicity and cheapness.

Swarf&Sparks
07-25-2007, 03:55 PM
google search string

peristaltic pump "tubing" "suppliers"

turned up over 40 000 hits

good animation of pump principle here
http://www.eccentricpumps.com/

oh yeah, shoulda remembered wikipedia

http://en.wikipedia.org/wiki/Peristaltic_pump

pcarpenter
07-25-2007, 04:02 PM
I think you will have spent more time designing and building this than the valve will save in metering out 100 gallons. I would presume, however, that you are going to fill 100, 1 gallon jugs on an ongoing basis rather than just once. If that's the case, I think I would weigh out what a gallon jug, properly filled, weighs and then think about using a solenoid operated valve triggered by something that measures by weight. Or, a fixture that plugs in the neck of each bottle and houses a fill line, vent line, and a liquid sensor that would trigger the solenoid valve and shutoff the motor.

Some of the stuff you may need might be at www.surpluscenter.com (http://www.surpluscenter.com)


Paul

Scatterplot
07-25-2007, 04:13 PM
Lol, time is the one element I have plenty of :)

Swarf&Sparks
07-25-2007, 04:37 PM
How precise does your "gallon" have to be, Scatter?

Scatterplot
07-25-2007, 04:43 PM
I don't know the actual number, but think "selling a gallon of milk" precise. This is for a friend who makes liquid stuff and sells it by the gallon.

pcarpenter
07-25-2007, 04:46 PM
Heh heh....is this liquid stuff something that used to be sold in Mason Jars?:D

Paul

Swarf&Sparks
07-25-2007, 04:52 PM
Then I'd go with metering by pump (like the peristaltic)
with maybe a "baker's dozen" rather than fancy level sensing.
Dunno about the legislation there, but over here "the man" gonna get ya if you sell short measure.

Evan
07-25-2007, 05:50 PM
So, basically what you need is one of these.

http://vts.bc.ca/pics2/gaspump.jpg

TECHSHOP
07-28-2007, 12:52 AM
I read this post the other day, but was having "computer issues".

Here is a link to the "gallon fillers page":

http://www.federalmfg.com/gallon.html

I think this is their "home page", kind of hard to tell:

http://www.federalmfg.com//index.html

No connection to the company, blah, blah, blah.

But, I think they are the "original" manufacture for this type of equipment, and it may be a bit larger than "you" have room for. I was looking for a "drawing" of the "squirt heads" and the "cam track". Basically the empty bottles are "pushed up" against the "squirt heads" as they "ride" around on the track, that "opens" the valve, then when the bottle is lowered, the spring in the "squirt head" closes the "valve" off.

In the small volumes you are "designing" for, I think a foot lever to raise and lower the bottles, one at a time, to a single "squirt head" should be "OK".

Hopefully you can use this info as a "launching point" for Google.

Mike W
07-28-2007, 01:52 AM
This is my high dollar oil pump for my headstock. Pump is one of those made to connect to a drill motor. Power is a Ford windshield wiper motor set to low speed.

http://img.photobucket.com/albums/v110/tek798/Lathe/oilpump.jpg

Guido
07-28-2007, 05:42 PM
Depending on viscosity of product, derivations of this basic pump/flow/fill scheme is used in filling tomato juice/paste/puree containers. Process is usually quite involved in automated filling of thousands of containers over a 24 hour period of operation. Elaboration may be proportional to product value.

http://i126.photobucket.com/albums/p86/Guido_album/jugfill.jpg

For a short run, manual operation, ease of disassembly/cleanup, cheap fabup of a prototype of PVC plastics, give it a try. The tip with flow resisting check ball should be as close as possible to the jug, helping to prevent post pump drip. The piston should have an adjustable stroke length, and will require adjustment over the first few fill cycles. Foot operated? Manual jug placement and retrieval. Cylinder fill should be via relatively large check ball of a density slightly less than product.

G