please help to me about control water pressure. it looks too diffucult to me.
Hi,
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http://forum.arduino.cc/index.php/topic,148850.0.html
How will you measure water pressure?
How high is the water pressure?
What will control the water pressure?
Is this a school/college/uni project?
Can you please tell us your electronics, programming, Arduino, hardware experience?
Thanks.. Tom.. 
it is a just school project. do you know that i am not experienced with working arduino. could you show simple example control water pressure with the sensors.
Javohir:
it is a just school project. do you know that i am not experienced with working arduino.
We can help with the Arduino part but you have to supply the know-how about controlling water pressure.
How would you control the pressure without a computer?
Pressure and flow-rate are closely related. How many litres per minute will be flowing?
What range of pressures do you want to deal with?
If the flow rate and the overall volumes are small one way to vary the pressure is by raising and lowering a header-tank.
...R
first, you need to learn about sensors. the Arduino does little without sensors.
the rule of thumb is that you get a sensor to detect your thing to be measured.
you have a a desired measureing point
you have a desired accuracy
then you have a sensor SPAN, the full distance or full range of the SENSOR.
then you have a sensitivity of the sensor.
The SPAN, idealy should be no more than twice your desired measurement
the SENSITIVITY, ideally should be able to resolve 4 times better than you want.
home water pressure is about 30-60 PSI here in the USA.
so a SPAN of 100 would be good. if one were to use a span of 1,000 then most of it would never be used.
Then the sensitivity, if it could read in only 1 PSI increment, and output 30, you would not really know if it was 29, or 30 or 31. if it were able to output in 1/10 increments, then a reading of 30 would be either 29.9, 30 or 30.1
point #2 : digital or analog.
if the device outputs analog, 0-5 volts (or 0-10v, or 4-20mA, etc) that will connect to an ANALOG input.
the analog input on the Arduinos have a range of just over 1,000 steps. so your 100 PSI sensor might be able to 'see' a 0.1 PSI change.
if it is a digital sensor, then the sensor will tell you what it can do.
so, your first requirement is to identify the PROCESS or THING to be measured.
then find a sensor.
maybe first, or sooner or later, google arduino water pressure and see what others have done.
use arduino in your search. arduino water pressure, arduino glove (over 400,000 hits) arduino kite (over 400,00 hits)
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all that was said about sensors goes for 'FINAL CONTROL ELEMENTS"
these are the valve or the thing that actually touches the process.
the device cannot be able to control 10,000 units, if you want to control only from 50-55 units.
it too has to have a range that fits your needs.
this is probably 1,000 times more important, and probably 1,000 less understood.
too often people do not understand that a pipe valve is not designed to control flow, but to be on or off.
a flow control valve is desired.
start with googling for your project, get some ideas, and get started !
Controlling water pressure is not easy! Measuring is quite straightforward (get a sensor suitable for your pressure range) but the control of the pressure is a whole different thing. The problem is that water is as good as non-compressible, so a tiny change in volume gives a huge change in pressure. You'd indeed use a water tower as described above, or a compression vessel like you see in central heating systems.
You'll have to understand what you really need to do to control your pressure (how to measure, how to adjust - is there flow? How much? System volume changes?).
Water must flow at a exact pressure. And I have three water pump. If the water's flow decrease, the next pump should work. if it is normal the first pump just work. that is the problem.
You need a buffer. Some kind of pressure vessel (partly filled with compressed air, partly filled with water). Then you can
measure the pressure, the moment you notice the pressure drops you have the second (or third) pump kick in.
The required capacity of this vessel depends on the flow, how fast demand changes and how fast a second pump can come online (it works just like a decoupling capacitor in an electrical circuit).
To keep pressure constant, it may be best to monitor and regulate the pressure of the air above the water instead, this is probably easier than for the water pumps. Then you need two limit switches: when the water level is too low, start the second pump. If too high, switch it off. You can even switch off the first pump when demand is low and still maintain pressure.
The role of the electronics is very minimal in this.
wvmarle:
You need a buffer. Some kind of pressure vessel (partly filled with compressed air, partly filled with water). Then you can
measure the pressure, the moment you notice the pressure drops you have the second (or third) pump kick in.
I have a system for the water supply on my boat that works like that. Of course it has only one pump. I can draw about 1 litre from the tap before the pressure falls and the pump starts.
There are no electronics in the system. The pressure is detected by a flexible disc pressing against a spring and pushing a microswitch.
Javohir:
Water must flow at a exact pressure. And I have three water pump. If the water's flow decrease, the next pump should work. if it is normal the first pump just work. that is the problem.
You have not told us what volumes of water are involved (litres per minute, minimum and maximum) and within what range the pressure must be maintained (minimum and maximum pressures). I reckon a practical system with no pressure variation would be next to impossible.
...R