Transistorized water flow?

[dyarker]

Retired USAF Master Sargeant. I maintain a PBX for the A.F. in Izmir under contract with ITT.<p>So, it's second or third largest city. Both Izmir and Ankara growing, so I don't know which is larger at the moment.<p>Uh just about like Colorado, a bit wetter in central. They export a lot more agricultural stuff
than they import. Humidity not too bad.

[Will]

I think this is probably the cheapest, if not the most effective way you could accomplish your wishes. Firstly - there is little point in trying to measure the level in the fountain bowl since you want to hold it constant at the level of the drain - so you need to sense the flow/level somewhere else - so get a pot, say something about the dimensions of a 39 oz coffee tin, into which the fountain bowl drain discharges. Fit an orifice (a) into the bottom or discharge of the pot so that the water out of the tin runs through it into your half barrel fountain. Get a simple level switch (One out of an old washing machine which I believe senses level by pressure/head and not physical level float). Arrtange the water flow via a solenoid valve which has an orifice (b) (Or a manually adjustable needle vale) in line with it. Arrange a by-pass around the solenoid valve and orifice (b) with another orifice (c) in it. In normal operation the solenoid valve is closed and the water flow rate, which is controlled by the orifice (c) is such that a takes a head of six inches or so to get the flow of orifice (c) through orifice (a) When the water begins to evaporate the level in then pot drops, the level switch open the solenoid valve and fills the pot at some pre-calculated rate. When the pot is at water level switch max the solenoid valve closes and you are back to normal operation. Sounds complicated perhaps but equipment wise it is simple. Give me the chosen flow rates and city water pressure and I will give the sizes to which to drill the orific plugs. In practice the flow rate determined by orifice (b) will be such that it will never conceivably be required to have it full open for a long period. The system will then act as a liquid/mechanical PWM system in which the water flow rate is determined by the mark/space ratio of the solenoid valve on/off periods.

[Engineer1138]

When I saw the words "Peltier cooler" combined with muscle wires I figured you're getting waay too complicated
Why not just go to Home Depot (or one of the many online surplus stores that are much cheaper) and get a solenoid valve for sprinklers? It will even fit standard plumbing.<p>You can sense water level electronically without much trouble... I'm going to start a project to do just this as soon as I have time (like you, I can't use a float in my application)

[haklesup]

Nothing less than a "Rube Goldberg" machine is required here. It looks like you will need a large cistern, an IR laser w photo sensor(used to sense temp and level of the water), several hundred feet of various kinds of tubing, a bag of 555 chips, 1 foot-3cm of Nitonal wire and a 500W power supply plus associated hardware and building permits. Oh, don't forget a PC operated data Acq and control system.<p>More seriously though. You can get RH% (relitive Humidity) by measuring temp with a wet and dry thermometer and using the difference as the trigger for your valve. Some kind of biased resistance bridge circuit might give you a difference signal with no active components but I am not very good with bridges. <p>When the two RTD's read the same temp, you have reached the dew point or 100% RH and you can turn off the water except to replace that lost to the birds. As the difference increases, the RH is going down and you need to increase flow. You don't need to know the values of the temp only the relationship.<p>RH has more influince on evaporation rate than temp alone. You can loose plenty of water even at 50F if the RH is very low. You can also have condensation at fairly high temperatures (the dew point can exceed 80F in some regions in summer)<p>Just in case someone is unfamiliar, the wet bulb thermometer does not get immersed in the water, it is damped by means of a cotton wick such that you measure the temp of the evaporating water.<p>(PS the old TV is fixed, See the other post)<p>[ May 11, 2004: Message edited by: haklesup ]</p>