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Q: water flow ( Answered,   1 Comment )
Question  
Subject: water flow
Category: Science > Instruments and Methods
Asked by: bruce12-ga
List Price: $25.00
Posted: 27 Dec 2005 05:54 PST
Expires: 26 Jan 2006 05:54 PST
Question ID: 610076
Advice on selecting valves to variably(possibly using a programmable
variable controller?) control water flow at different rates(maybe
every 15 seconds) through maybe 1/4"tubing. Water simply is gravity fed(not
under pressure)and accuracy is fairly important, and the less
sophisticated the better.  Flow range is as low
as 2 cc per minute and as high as 1000 cc per minute. Any detailed
info on how to do this would be appreciated as I am not an engineer. 
Thanks-bruce12

Request for Question Clarification by redhoss-ga on 28 Dec 2005 07:16 PST
I can describe how to do this and give you links to material about the
components required. Would this be sufficient or do you want an actual
design.

Clarification of Question by bruce12-ga on 29 Dec 2005 04:29 PST
hi, i am looking for advice on how to build this, so anything you can
offer would be appreciated. A design would be great but dont know how
much you can offer.  Thanks for your help-bruce
Answer  
Subject: Re: water flow
Answered By: redhoss-ga on 29 Dec 2005 07:39 PST
 
Hello Bruce, when I first read your question it sounded like you were
trying to make an IV drip. There has been quite a bit of work done on
your exact problem. The idea I had was to use a stepper motor to
control the drip and then to control the stepper/valve with a PC. I
searched using "stepper motor IV drip" and found some interesting
information:

http://www.di.ufpe.br/~pish/cadis/asap971.htm

In this paper we present the development and implementation of an
intravenous infusion controller system based on fpgas. The system
receives information of an infusion drop sensor and controls the drop
flow by giving the direction and number of steps of a stepper motor,
which compress the drip-feed hose. The system consists of a mixed
implementation of software and hardware. The software was implemented
in C++ and the hardware was implemented by using FPGAs.
 This is a pretty detailed description of a system that will do
exactly what you require. I understand that you wanted something
simple, but what you want is not that easily done.

http://www.matrixpd.com/ps-medical.htm

IV Bag Drip Rate Flow Control Valve
We designed a flow control valve using a stepper motor control and
weigh scales. This project proved that a reliable valve could be
developed to control and monitor the drip rate of an IV bag. We also
developed a custom Windows user interface to enable researchers to
easily adjust drip rates and capture data.
This is another company that has designed a drip control using a
stepper motor. Instead of counting drops, they use weight change to
calculate flow rate.

If you don't want to stick with the gravity flow concept, here is another approach:

http://www.knf.com/knflibrary/magmetering.htm

The positive displacement metering pump is generally the first choice
for providing precise and repeatable flow in many medical device fluid
dispensing applications. Understanding the full range of established
and newer metering pump technologies available allows for the
selection of the best metering pump to meet the fluid handling needs
of the application.

Here is a patent application for your device:
http://freepatentsonline.com/4038982.html

Electrically controlled intravenous infusion set , United States Patent 4038982

An electronically controlled intravenous infusion set of the gravity
feed type having a flow path including a drip chamber and an internal
valve for regulating flow through the set. Electromagnetic valve
operating structure, positioned outside the IV set, controls the
internal valve in response to an electronic control system. The
electronic control system serves to open the valve to allow a drop to
fall, and includes a control circuit. The control circuit includes an
optical drop detector, associated with but positioned outside the drip
chamber, which senses the falling drop and signals the control circuit
to close the valve. The control circuit also includes a variable
frequency clock and associated digital selectors for affording an
attendant the ability to precisely select a desired drip rate. An
alarm system, operating on digital principles, senses high drop rate
or low drop rate conditions and, in response thereto, puts the control
system into an alarm condition. The alarm system includes means for
digitally adjusting the sensitivity thereof to provide high
sensitivity at low drip rates but to decrease the sensitivity at
higher rates so that premature alarm conditions are avoided.

I hope this will give you some good ideas. If I have misunderstood
what you are looking for, please ask for a clarification and I will
try and help.

Good luck with your design, Redhoss
Comments  
Subject: Re: water flow
From: myoarin-ga on 28 Dec 2005 06:11 PST
 
Bruce,
As I understand it, you want a valve that can be computer controlled
to deliver a varying amount of water per minute, which flow can be
changed fairly frequently.

Maybe a solenoid valve from one of the producers listed on this site does that:
http://www.thomasnet.com/products/valves-water-flow-control-solenoid-91451856-1.html

I don't understand the details on the companies' sites, but there are
many details, as you requested.

Good luck, Myoarin

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