Stepper Motor for Needle Valve Temperature Control

[5wp]

Not my area, but I'm trying to put together a device with a PID that would control two steeper motors on needle valves( one hot and one cold) to give me constant water temperature flow.
I want to keep it simple.
Any practical ideas, on sourcing stepper motors, needle valves etc.
Thanks

 

[MikeHalloran]

Keeping it simple suggests a thermomechanical valve, commercially available, with no electronics required.

Stepping motor controls and drivers are getting cheaper, but not simpler, all the time.


Mike Halloran
Pembroke Pines, FL, USA

 

[5wp]

thanks Mike
The new PID's seem easy enough to set up with a thermocouple etc. It gets more complicated picking out proportioning valves and some sort of stepper motors to adjust the valves.
The application is to be used in a photo lab to give a specific water temperature.
Unitys are available but very pricey.
Thanks again,

 

[MikeHalloran]

If you keep track of your own labor while integrating and tuning the system you propose, you won't think the dedicated controls are so pricey anymore.

If you're doing it for self-education, that's a different story.


Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

The issue is that you need to control two things - flow rate and temperature, so you really need a flow measurement / controller which ramps both valve up at the same rate / amount and then a temperature controller which affects each valve differently.

You will need constant CV % valves ( I think) so that you could set say 40% open for both valves to get flow and then vary the % of each to get your temperature (say one 25% open and the other 15% open. Also need identical pressure at the valve inlet on hot and cold systems.

Otherwise your two systems will fight each other. If you have tow systems then both will fight each other and your temperature valves could be either wide open or nearly shut, providing the right temperature, but the wrong flow or the right flow but the wrong temp.

how specific a temperature range do you want and over what sort of flow range (Min flow to max flow as a %).??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moltenmetal]

Why not just buy one from Hass Manufacturing?

https://www.google.ca/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=hass+intellifaucet+d250

There are several problems here:

1) These devices have no deterministic failure position. Not great if you lose power while the faucet is on...
2) They don't have torque feedback, so they're going to have trouble with tight shut-off

But they do work, after a fashion.

 

[5wp]

Thanks for feedback guys. I know that manually adjusting two/three valves can be annoying and time consuming. Been there done that. I have also looked into Haas's product line. Feedback varies on satisfaction, cost etc.
My thinking was to have one manual valve(rotometer) controlling the outflow. This then leaves the hot and old lines. The cold water inflow line could also be set manually as the water temperature here will always be below my desired temperature. This then leaves the hot water inflow line that could be controlled by a pid/thermocouple/proportional valve/stepper motor arrangement.
The water flow volume is between 1-2gpm (spprox. 10 liters)per minute. The ideal outflow temperature needs to be between 68-70 F.
Is this over simplistic, or am I missing something?
Thanks again for the feedback.

 

[moltenmetal]

Persisting in building something you can buy for so little money is puzzling.

If you want something even cheaper, a PWM-driven proportional solenoid valve will work, without the lack of a deterministic failure position. Both Burkert and Asco sell them.

 

[LittleInch]

Sounds like a shower mixer to me. Depends on the model but many are really quite accurate in regulating temperature and flow. Some are even digital.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moltenmetal]

Another very good suggestion.

 

[Compositepro]

Is this a once through cooling system? That is illegal in many areas these days because of the burden it places on water and sewer systems. If this is a recirculating system, then you should be controlling heaters and chillers, not valves.

 

[5wp]

Thanks again. With reference to so little money. I pay 30% exchange rate on Canadian to US
money conversion, that with the high shipping charges, places a $700 item at over $1100 US.
With respect to sewer systems that is not a problem as this area as we have independent septic/septic beds.
I will check out the Asco and Burkert lines of PWM proportional solenoid valves.
Thanks again for the feedback.