This is a 2-part question, 1 mechanical, but I thought to place both here:
1st) I've connected a clear piece of PVC pipe on a retort stand to measure WVO usage over time. I noticed then that there is a huge pulsating effect coming from the Lister CS fuel pump, squirting fuel back in the opposite direction while running. Is this normal and would a check valve in line to prevent this be a problem? In other words, where would the excess fuel go if it cannot go back the pipe ??? I'll hate to try and read the flow rate on the High Pressure fuel line side!
2ndly) I ask this 'cos I want to measure fuel flow with some type of sensor and I think this might affect it or more accurately, make the sensor that compensate for this, more expensive!
To the question, does anyone know of a production vehicle that might have a fuel flow meter installed? I presume some fuel injection units might have them, so that I can look at the junkyards for one to use ???
Thanks guys,
dubbleUJay
good luck with measureing fuel flow on your engine, you have the return line coming
off the injector to contend with and between all the interactions and the fact that
the flow rate is so low,, i just don't see it happening with any degree of accuracy
now if you are using a day tank, perhaps you can measure fuel rate of consumption by
weight, which would be far more accurate in my opinion anyway.
measureing by weight and not by volume is the great equalizer of fuels, and where the rubber
meets the road in getting really good test results,
so if you are going to go to the trouble, and given the fact that this is a stationary application
it seems to me that logging by weight would be not only easier but more accurate.
thats the way i see it, ymmv of course
bob g
BobG, I want to measure short runs, so I've got to see if I can measure it accurately electronically. I can probably use 2 sensors (Supply & Spill) and subtract the 2 values from each other, but the big problem will be the cost of such accurate sensors. (800ml of diesel for a hour = approx. a flow rate of 10ml/min) Before you say anything about the figure, its just a ball park I've got in mind! ;)
Weighing the fuel like you said will be the answer, but how to implement it electronically in real time ???
dubbleUJay
why not sample the weight, and log the value
sample again in perhaps 6 sec, and log that value
subtract one from the other and multiply x 10 or whatever
to get the value used over time?
that of course could be factored by the amount of power generated to get
a bsfc in gr/kw/hr.
or so it would seem to me, especially for you fella's that are intent on automating these things
and programming far above my ability or desire to learn.
in reality something like that would have to happen if you were to do it with a flowmeter anyway
a flowmeter telling you the amount of fuel passing the line is useless without being factored against
time and load, would it not?
a flow meter that simply states 5 gallons have passed doen't really tell me much, without knowing
how long it took to pass, and under what load the engine was under.
so even if you use load you still have to have a start value, a timed event, and end value, and computation
made to determine the volume that has passed, then factor that against load and some sort of time multiplier to
make it work out in some meaningful value.
or so it would seem to me.
it just seems to me if i were to go to all the trouble to work out all the programming and hardware, i would at least
look into using weight instead of volume because weight of the fuel is much more useful than volume, volume changes with
temperature and the btu content is largely unaccounted for.
weight seems to account for temp and btu fluctuations of the fuel to a large extent.
thoughts?
bob g
dubbleUJay
I doubt you will find a fuel flow meter in any junk vehicle. The cars that have mileage computers use the pulse width signal off the fuel injectors to calculate fuel use against time and miles driven. Anyway that is how I understand the system, could be wrong though.
I voter with bob, balance your fuel tank on a weigh bar and go with that.
Billswan
Quote from: mobile_bob on November 17, 2009, 05:02:44 AM
a flow meter that simply states 5 gallons have passed doen't really tell me much, without knowing
how long it took to pass, and under what load the engine was under.
thoughts?
Yes Bob, your right on, the time and load will be available with the other sensors in my setup and from there the calculation will be made.
I have to way up the cost against accuracy though, I can buy a commercial one for more than the whole system is worth, but on the other hand I need acceptable accuracy. A difficult one, but maybe a crude meter can be calibrated with a few test runs by entering a constant into the computed formula. I just dont know at this stage.
Your weighing idea will still be the best I think, but one would have to make some sort of inline device that would hold say 1kg of fuel and then auto-fill itself when empty for long runs or just have a separate container on an electronic scale type setup, probably a strain gauge to interface to the rest of the system.
Its probably impractical to way a large amount of fuel.
Still, if a VW Jetta or BMW315i had something like a fuel flow sensor in them, it could be calibrated with software to give very close reading I would think.
I just don't have any knowledge if any oldish vehicles had them in ???
dubbleUJay
Quote from: billswan on November 17, 2009, 05:42:02 AM
dubbleUJay
I doubt you will find a fuel flow meter in any junk vehicle. The cars that have mileage computers use the pulse width signal off the fuel injectors to calculate fuel use against time and miles driven. Anyway that is how I understand the system, could be wrong though.
Billswan
Billswan, thanks, I'm also not sure how they do it, but then they must know how much fuel are being released with a given pulse duration or "voltage", again a set number they must put into the calculations.
Well there goes the easy way out ;)
Weighing will involve quite a bit of hardware, not the electronic type, but the scale mechanism. :'(
I'll probably leave this for one of the last things to impliment for my project.
Thanks for all the input guys.
dubbleUJay
Jens, would using a very small ID supply pipe not give more "detectable" flow ???
Obviously up to the point that the fuel will actually gravity feed.
dubbleUJay
I did the same as you this morning, looked all over for meters and came up with nothing! :'(
I did get DIY circuits for ultrasonic and magnetic sensors, I'll look at them again. From there the 1st question about the pulsating fuel in the line going back and forth! I doubt that they would be accurate though.
here is a possible solution to the problem/project
use a small tank, that can either be weighed or of suitable volume
decide which you would rather measure, volume or weight
we will call this small fuel tank a day tank
and i will illustrate how i would do a weight based solution
set the tank up on some sort of balance beam with limit switches at the high
and low mark, these switches will be used to do two things, one is to control a small pulse
electric fuel pump to fill the tank to the upper limit and also provide a reference signal to your puter
to tell it that the fill cycle is complete. the lower limit will turn on the pump and send a reference signal
that a fill cycle has started.
the fill weight can be calibrated easy enough to determine exactly how many grams it takes to function both
limit switches, and the puter can keep track of time, load levels and do the calculations, and post a total
bsfc for each cycle,
if the cycles are short in duration one should be able to get a chart that would be useful in determining bsfc
at various load levels on the engine.
as for doing in in volume, you simply could use a brass toilet float to control the limit switches and calibrate by volume
between on and off cycles.
the key is to log only full cycles, and forget the part cycles and not being relavent.
it appears you want to do logging over the long run and not short run tests anyway, so this looks to me like a possible solution
that could be done fairly inexpensively and will be as accurate as your attention to detail.
bob g
Quote from: mobile_bob on November 17, 2009, 09:35:53 AM
it appears you want to do logging over the long run and not short run tests anyway, so this looks to me like a possible solution
that could be done fairly inexpensively and will be as accurate as your attention to detail.
bob g
Thanx again Bob,
Actually, I wanted the measuring to be for both, long & short runs, so that anyone can use it, depending on their setup. I'm not just thinking of my specific setup.
Come high or low water, I'm going to build this thing if I can, I'm just trying to make it universal and easy as far as possible from the beginning.
Obviously if it cannot be done a simple way, it cant and I'll have to look at something else. :(
WildA$$IdeaTime
What about a drip meter like an IV?
Murphy Drip Meter (pic) (http://www.grahamfield.com/content/viewzoomimage.aspx?productid=299) + a LED/photodetecter setup to count the drops.
Don't know the max flow rate or if they can be paralleled. Though IIRC my old food pump that used a drip chamber, was at least capable of 400ml/hr.
Viscosity will prolly affect drop volume, so thinking it would require a one time calibration against weight for different fuels.
Murphy drip meter - retail (http://ucanhealth.com/goto.php?page=detail.php&graph1=3525)
Quote from: ndavid79 on November 18, 2009, 10:24:05 PM
WildA$$IdeaTime
What about a drip meter like an IV?
Murphy Drip Meter (pic) (http://www.grahamfield.com/content/viewzoomimage.aspx?productid=299) + a LED/photodetecter setup to count the drops.
Don't know the max flow rate or if they can be paralleled. Though IIRC my old food pump that used a drip chamber, was at least capable of 400ml/hr.
Viscosity will prolly affect drop volume, so thinking it would require a one time calibration against weight for different fuels.
Murphy drip meter - retail (http://ucanhealth.com/goto.php?page=detail.php&graph1=3525)
Not such a "WildA$$Idea" David as I also thought about something to that effect,
well maybe the others would say 2x WildA$$'s makes a whole @$$!(http://www.stationary-engine.net/forum/images/smilies/toomuch.gif)
Anyway, I just don't know how one would automatically increase/decrease the flow-rate when the fuel demand varies without making it very difficult ???
dubbleUJay
These are passive devices actually, the natural flow to the fuel pump causes the drip rate. Being sealed, fuel flow stops = drips stop, low flow = slow drips, high flow = fast drips. But at some point drips can't keep up and it become a stream.
Quote from: ndavid79 on November 18, 2009, 11:08:37 PM
These are passive devices actually, the natural flow to the fuel pump causes the drip rate.
Well that solves that problem, I didn't think of it that way. I'm still reading up on the links you provided, but I presume there's some sort of vacuum involved then or the air gets trapped.
Funny thing is I had a lot of IV's in me during my life and never thought about how they actually work! I suppose when your lying in hospital one's got other things to worry about though! ;)
I'll check it out some more and I don't think counting the drops would be a big problem electronically, my Lister on an IV would look cool though ::)
You've modified your post while I was typing hey! ;)
That answers my assumption.
I think the maximum flow-rate would be:
1 liter per hour (Just taking an approx. figure of a Lister CS single for argument sake)
thats 1000ml/60min=16.7ml/min we need to get droplets for and not a stream. Lets call it 20ml/min to be on the safe side as the Changfa's uses a lot more fuel. ;D
I dont even know if that will be enough for them, I'll ask Bob (http://www.stationary-engine.net/forum/images/smilies/blasted.gif)
If I still have a bag for my old food pump, I'll see how fast it can flow while maintaining drops, by this weekend.
The air (or a purge gas) in the top half is a critical part of the system... As the pump draws the level of the fluid in the lower half down, the air pressure inside reduces, inducing another drip to replenish.
Quote from: ndavid79 on November 19, 2009, 01:04:41 AM
If I still have a bag for my old food pump, I'll see how fast it can flow while maintaining drops, by this weekend.
The air (or a purge gas) in the top half is a critical part of the system... As the pump draws the level of the fluid in the lower half down, the air pressure inside reduces, inducing another drip to replenish.
OK Dave, if I may ask, what is a food pump ???
It probably has another name over here, but I cannot place it!
I have whats called a g-tube style feeding tube, for my primary nutrition (due to my Duchenne MD (http://www.mda.org/disease/dmd.html), I can't swallow enough to maintain weight).. The food pump I'm referring to pumps formula from a refillable bag, and through the g-tube at a user set rate, much like an IV pump.
Kangaroo Feeding Pumps (http://www.tycohealth-ece.com/index.php-folder=41.htm), the 2100 looks my old one (recently got switched to a different style pump).
The Kangaroo pump uses a drip meter to watch its own flow rate & detect a plugged line or closed valve.
I had no idea it was a medical device David, thanks for that info. I actually was under the impression that its something used in the kitchen!!!
I just hope we wont infringe on any copyright stuff if we make one to feed "food" to out engines though. ::)
how do you figure a changfa uses a lot more fuel than a lister/oid?
my bet is a 12hp changfa 195 will compete very favorably with a 12hp lister/oid at full load particularly
and maybe across the load spectrum as well,
curious how you arrived at that conclusion
bob g
Quote from: mobile_bob on November 19, 2009, 09:04:46 AM
how do you figure a changfa uses a lot more fuel than a lister/oid?
my bet is a 12hp changfa 195 will compete very favorably with a 12hp lister/oid at full load particularly
and maybe across the load spectrum as well,
curious how you arrived at that conclusion
bob g
Hi Bob, I've got a feelin' your smileys are turned off ??
I just about bit my tong off when I stuck it in my cheek while writing that "comment" ;-) Sorry!
GOTCHA!!!!
;D
bob g
Now, i have no idea if this one would work, but i do see the possibilities.... (See pictures...)
Inside, there's a rotor with 6 blades, which spins very fast when blowing very lightly into it. I've never really testet it, but i think it is a part of some soda/beer dispenser system...
It needs some power (4,5v-24v) input, and there's some magnets on the rotor, which i guess gives pulses when it rotates... :)
Edit:
I found what looks like the specs for the one i have; it's for beverages only, and have a min. flow of 0,22 liter/min, but they do have similar flow meters for oils etc with min. 0,06 liter/min.: http://www.digmesa.com/digmesa/upload/pdf/FF/934-2540_GB.pdf
There's jewelled bearings, and they're easy to disassemble for easy cleaning (just twist apart), so i think they're rather tough... :)
Yes, 3,6 litres/hour would probably be in the upper range for several of our engines, but with two of these; one on the input side, and one on the return, the flow would be much more than that, and the difference would be fuel consumption...
Guys, so far it seems that even a commercial unit are hard to come by if available!
ndavid79's idea with an IV drip meter seems "practical" in theory.
Something that might be considered, also indirectly from one of the links David provided on another thread:
http://www.edcheung.com/automa/rain.htm
A DIY electronic rain meter, obviously not to that scale and probably inside the Drip Meter to auto-regulate the flow.
Would that be to complicated to manufacture with regularly available "stuff"?
This should give an accurate output over a short time, depending on the size of the 2x "containers" to fill ???
Almost like Bob's weighing idea.
dubbleUJay
PS-OK shoot the idea down! ;)
Jens, I though this idea might "tickle your fancy" ;)
I was thinking though of incorporating the tipping buckets INSIDE a drip tube (sort of a "vacuum" as in an real IV, "vacuum" is not the right word, probably a set volume of air) so that the drip-rate would work automatically as David explained before and using it directly inline with one's current fuel supply.
This will stop us having to worry about start/stop of the drops as the fuel demand changes.
I just don't know if it will work on a bigger scale and if it can be done easily.
The electronics involved would be simplistic, just a switch/mag/IR-gap or such to count the tipping of the buckets and multiply that with the volume per bucket. (I presume the electronics should be on the outside "looking" through the glass or whatever)
Obviously the smaller the buckets, the better.
I've got to think some more! :-\ Maybe it cannot be done easily and a cutoff like you said would do the trick!
dubbleUJay
PS- If all goes well, the guys from East will steal" this idea and we can buy it over the counter next month! ;D
OK guys, while you's in the US were sleeping, I did a test 2day. (I'm about 8h's ahead here in ZA!)
Here's a short description of an "alpha" drip-counter I made this morning:
(Picture at the bottom, bit out of focus, sorry)
I took a piece of 20mm ID PVC pipe and worked out that I need a piece 63mm in length to get a volume of approximately 20cm3 in the whole tube (1ml = 1cm3)
Then I cut it in half at an angle of about 33.3deg and glued the 2 pieces back to back onto a thin flat piece of plastic.
The plastic piece in the middle of the 2 angled pipes extrude at the bottom of the whole "thingy"
I started to cut it shorter in stages to find a medium where it will tilt when full. Not sientific, but it sticks out about 1/3 of the OD of the pipe.
This is how it operates:(Its my 1st vid on uTube, so please excuse the quality!)
http://www.youtube.com/watch?v=-QzedNZP1_k
It difficult to see, but I accelerated the water to a stream (not dripping) to illustrate the action faster.
I've made a mistake with my calculations somewhere I think as it only takes 5ml to tilt it to one side, but then it also does not fill up completely before it toggles.
Now I need to put this at the top inside a sealed container with inlet/outlet top/bottom and hope it does not flood the whole container past the counter ???
dubbleUJay
Ndavid79 has a good idear. My mom-in-law is on a feeding tube. And wife is a nurse, and brings old IV solution sets home to hydrate her 20 year old cat with failing kidneys. So I'm familiar with the setup.
It seems you could use an IV drip chamber http://www.stockphotospot.com/iv-infusion-drip-chamber-stock-photo-a24812.jpg (http://www.stockphotospot.com/iv-infusion-drip-chamber-stock-photo-a24812.jpg) and place an IR LED on one side, and a detector on the other side (cheap at Radio Shack), and use the output to trigger a transistor to pass a pulse of 12V to trigger a $7 electronic counter https://www.surpluscenter.com/item.asp?UID=2009112012282149&item=21-1498&catname= (https://www.surpluscenter.com/item.asp?UID=2009112012282149&item=21-1498&catname=) ?
Then you could calibrate by counting the number of drops required to total whatever unit of measure you are comfortable with (mL, ozs.?) and convert drops to volume or weight of fuel. Drop size for diesel will depend on temperature and surface tension of the particular fuel you're using. Then count number of drops per unit time and calculate the flow rate.
Place the IV drip chamber between the tank and fuel filter and (I think) the air contained within the chamber should dampen out the pulses caused by the injection pump.
Quinn
I like NDavid's idea and I agree with Quinn, the drip measurement is going to be much more accurate than tilt buckets, and if you can't get the flow rate, just add a second unit.
I played with an IR LED and phototransistor around a dripper many years ago. It does work with water and I don't think fuel would make a difference.
Quote from: Jens on November 20, 2009, 10:43:43 AM
One thing that I am concerned about .... let's say you require 10 ml to tip the bucket. You have 9.5 ml in the bucket and an additional drop comes in giving you 10.5 ml and the bucket tips. You would register only 10 ml.
Jens
Jens, one will have to let the thing run over a longer time period and then divide the volume of fuel versus the amount of tilts to get an average. Each DIY "tilter" is different, because its so difficult to get both sides exactly the same and also the center of gravity.
That said, one should be able to get a very accurate average, I would thing to a resolution of 5ml per tilt.
Anyway, my experiment might be retired to my weather station in the future, (I was looking for something with a finer resolution as we dont get to much rain here) if David's drip meter can supply 20ml of fuel per minute without turning into a "stream" of fluid.
That will save a lot of hassles. (He mentioned he will try and have a look at it this weekend, I just hope it does work.)
David, if you do see this post before you try it, do you perhaps have some vegetable oil you can try in it once it does work with something thin like water? That should be the 2 extremes that we might use. Even if it does not work with your tube, I'm sure we can make something that will, its just nice to have some type of dimensions to start off with ;)
dubbleUJay
Did some google research on IV drip chambers, check this out:
IV Administration Set 10 Drops/ml 72" Long (http://www.mountainside-medical.com/products/IV-Administration-Set-10-Drop-72%22-Long.html)
Not only dirt cheap, but at 10 drops/ml, thats 3.3 drops/sec at 20ml/mins. Looks doable.
Water & Veg oil, good idea, I'll see what we can do.
ETS: looks like they'll ship to practically any country.
Quote from: ndavid79 on November 20, 2009, 11:02:08 PM
Not only dirt cheap, but at 10 drops/ml, thats 3.3 drops/sec at 20ml/mins. Looks doable.
David, this IV seems to be 10drops = 1 milliliter (1cm3) of fluid, but I cannot see the flow-rate anywhere ???
How did the experiment go with the tube? I hope you didn't use your own one! ;)
dubbleUJay
Post amended:
Now this looks very interesting for a standalone application!
http://www.freepatentsonline.com/4681569.pdf (291kb)
I don't know if they are available commercially though, does someone in the US knows?
With a bit of tinkering the idea will work for my PC application, I particularly like the way that it reads the drops!
Still, now to find an IV that will give the required flow-rate ::)
Quote from: dubbleUJay on November 23, 2009, 09:49:44 PM
David, this IV seems to be 10drops = 1 milliliter (1cm3) of fluid, but I cannot see the flow-rate anywhere ???
Ya, unfortunately I haven't found that spec anywhere, for any such device. But I think 3 drops a sec is doable
Quote from: dubbleUJay on November 23, 2009, 09:49:44 PMHow did the experiment go with the tube? I hope you didn't use your own one! ;)
Haven't gotten to do it yet, maybe tomorrow! No, it won't be connected to me, lol. ;)
I plan to use a plain bag, hook it up to a suction pump with a reservoir to simulate an engine's fuel pump, & adjust the bag's flow clamp to find where drips become a stream. Then adjust back to max drip rate and time a 100ml via tick marks on the bag (don't know the drops per ml on these).
Quote from: dubbleUJay on November 23, 2009, 09:49:44 PM
David, this IV seems to be 10drops = 1 milliliter (1cm3) of fluid, but I cannot see the flow-rate anywhere ???
Quote from: ndavid79 on November 23, 2009, 10:35:15 PM
Ya, unfortunately I haven't found that spec anywhere, for any such device. But I think 3 drops a sec is doable
OK, I see what you meant, I thought you were under the impression that the 10drops/ml mean it will give a flow-rate of 3drops/sec ???
Obviously you were referring to what WE actually need. :-[
I probably sometimes come across as a bit :P, but English isn't my 1st language and I've got to read stuff a few times! ;)
Did you look at the Pattern for a drop counter in this link?
http://www.freepatentsonline.com/4681569.pdf
I amended my post & I'm not sure you saw it.
Not exactly what we need, but a start. I haven't seen anything like it in ZA hospitals, maybe by you guys?
dubbleUJay
if anyone has an old weather station with a rain gauge you could probably convert the inches of rain into gallons of fuel, just an idea, by the way I do have one around and I will give it a test when I get back from Vacation.
Hi Carlb, not to shoot you down, but we're trying to automate it as far as possible to either an digital meter or for that matter a data logger in the most affordable and simple way if possible.
Enjoy your vacation, some of us has to fiddle with µCogen stuff to relax! ;)
dubbleUJay
1st test with water done!
At fastest drip rate (that was quite visible), it flowed 100ml in 3:30, which by my math is 28ml a min. Visible estimate of drip rate, ~4 a sec.
Quote from: dubbleUJay on November 24, 2009, 06:19:28 AM
Hi Carlb, not to shoot you down, but we're trying to automate it as far as possible to either an digital meter or for that matter a data logger in the most affordable and simple way if possible.
Enjoy your vacation, some of us has to fiddle with µCogen stuff to relax! ;)
dubbleUJay
I had to take my vacation this week, I am starting my 11.2kw ground mount solar array install next week (that will give me a total of 22.2kw of solar panels on my property)when I get back from vacation.
this internal workings of the rain gauge i am talking about is exactly the same principle as what is being discussed here with the swinging see/saw microswitch, each time the water comes down the center of he rain gauge housing it flip flops the see/saw and trips the microswitch. Just a thought :)
carl
carl
Hi Carl, I wish I had some more solar, only 2x 75w panels on this side and we have ample sunshine in South Africa, but as always (in my case anyway), $$$ talk! :'(
The idea for the "see/saw" came from a rain gauge, it will work I'm sure, but it seems that the general feeling in this thread is that it might not be very accurate, or as accurate as David's IV drip-meter.
David's idea seems to be the best one so far if it works IMHO anyway.
Lets see what he comes up with and take it from there, we might come back to the rain gauge, I don't know at this stage.
Good luck with the solar installation, please open a thread in this forum about your progress, I for one would be very interested and I'm sure a lot of other guys as well.
Quote from: ndavid79 on November 24, 2009, 08:43:33 PM
1st test with water done!
At fastest drip rate (that was quite visible), it flowed 100ml in 3:30, which by my math is 28ml a min. Visible estimate of drip rate, ~4 a sec.
Great David, now I suppose that the "proof is in the pudding" if it works with VO! ::)
Water: 100ml in 210sec= 0.476ml/sec and that's 28.57ml/min, you're quite correct!
I've got a feeling that the VO will be substantially less, but I'm sure if the orifice of the dripper is made bigger we can get an acceptable drip-rate for VO.
I wish I had the formula that the guys use to make these with, I presume it has to do with the surface tension of the fluid as well, but this will probably be a hit&miss thingy!
I'll wait till you come back with the VO test run and then I'll probably built one here, I've got some clear PVC piping with removable end-caps that might work, we'll see.
dubbleUJay
I'll be very curious to see if the low surface tension of any oil will allow much dripping to be measured. I think there will be a tendency to "stream" at anything but very small draw rates...
I wish you well...
In the trade, very low flows are measured by differential pressure across an appropriately sized orifice plate in the line. After calibration, these are extremely accurate... but pricey...
Cognos, I saw those somewhere and clicked away when I saw the costs! Also I don't think there was a way to make them DIY, but maybe I should look at it again if the drip-meter doesn't work, I forgot about those, thanx! :-[
I think it was when I was looking for an oil pressure/flow sensor for the low pressure from the ListerCS oil pump IIRC.
Orifice sizing should handle the oil viscosity issue , I think. You can buy an IV drip set at any drug store here in the US without a needle.
Viscosity of oil varies with temperature, so for good accuracy, you will have to calibrate with a measure at a range of temperatures, and add fuel temperature to your drip table lookup for calculations. The fuel temp might be measured with an epoxy puttied LM34/35 right near the dripper (stuck in a cut off barb Tee).
The beauty of the IV dripper is the demand vacuum regulated flow rate, the gravity tilt doesn't get you that.
One thing to watch is the tubing length. My idea was that you'd probably want to cut most of the tubing off the drip set, perhaps keep the flow shutoff/regulator, though. If you know a nurse, you should be able to sweet talk a used IV administration set or two out of her/him. It will contain a drip chamber and a flow regulator/shutoff.
You can adapt to the tubing with barbed fittings available for vacuum lines at the auto parts store.
Quinn
Quote from: cognos on November 25, 2009, 08:49:57 AM
In the trade, very low flows are measured by differential pressure across an appropriately sized orifice plate in the line. After calibration, these are extremely accurate...
Cognos (or anyone else for that matter), I'm off topic now, but can fluid pressure be "amplified" by hydraulic action?
In other words, can I use a sort of master/slave setup on a low-pressure line to amplify the pressure proportionally and use a pressure gauge of higher calibration and work out the pressure from a pre-defined chart ???
dubbleUJay
PS-I'm still going to find a way to read my "low" oil pressure on my CS! ::)
I suppose those small pressures can be passed through a mechanical actuator and amplified with another pressure sensing cell. But that would add hysteresis (present in all pressure measuring equipment) and possibly compound errors in the original measurement...
The way it's done in the trade is the pressure is converted to a milliamp measurement in an appropriately-sized differential-pressure-measuring cell (measures the diff in pressure between the high and low pressure sides of the orifice, independent of the actual pressures). This milliamp signal is what's actually measured and calibrated, not the pressures.
In the old days, the actual pressures were measured on either side of the orifice - sometimes by gauges, often by mercury-filled manometers(!) and then the flows would be calculated from a chart.
Your problem here is the pulsating nature of the flow, and it's small/low flow/low pressure nature.
The pulsation can be fixed with a check valve (to prevent backflow) and a surge tank. The rest of it is not lending itself to a cost-effective solution...
Here's a crazy idea... your injection pump is essentially a variable-volume reciprocating pump, yes? If you knew the pump volume at "rack closed", and at "WFO", and a few points in between, could you not connect some sort of positioner/variable resistor setup to sense rack position that could be run through a microprocessor to give you something like the fuel-injector scenario in a car?
Then:
(Rack position sensed = pump volume in mls) X rpm/2 = mls/minute
Cognos, thanks for the explanation. I see that electronic pressure sensor IC's are getting much more affordable these days and might incorporate one of those in the future, alas, I can get one for that low pressure!
Believe it or not ;) I did look at the pump rack in that way, but I wasn't sure how accurate it would be, even using the control rod into the pump, there's some "lash" in the gearing and mine seems to constantly move in & out all the time with a constant load on the engine. (I'm not sure if this is normal and I was going to address this in a new thread in the future, but my pump was refurbished by a shop that's suppose to know what they're doing!)
The cct in a PC mouse would read the movement quite accurate though!
HELLO
Did this project just die - any updates on what worked? Will go with the IV type since I have a few from last "care giver visit".
Dick ???
Sorry I dropped off the project guys.. Right after the water test, my supply company decided to go assain & hold my next shipment of formula (which we had a surplus of) & feed bags (which is impossible to form much of a surplus due to various issues with said company) hostage for 2 weeks over a billing issue that was their fault (they decided to forgo properly filling out claims to my 2 insurances, build up a bill & then ask for a CC#)... So hadda use that last old style bag (the kind w/ drip chamber) when the last new style bag (read cheap) sprung a leak after 3-4 days reuse.