I am attempting to build a water control system which allows proportional control of the water output flow.

I had initially thought of using servo-controlled ball valves, but it was suggested that solenoid valves can be modulated using PWM or similar input and thus end up with a somewhat variable flow rate.

However, I just tested a diaphragm/direct lift solenoid valve (like this one from ebay) using different input frequencies and duty cycles, and was unable to achieve anything other than a "full on" and "full off" condition.

Must I use a "direct acting" solenoid instead, in which the solenoid plunger directly controls the flow?

or does someone know if it's possible to modulate the diaphragm-type valves? If so, what frequencies and duty cycles would be most effective?

Valve requirements

  • Standard (US) municipal water source (50-100psi)
  • 3/8" to 1/2" water supply line
  • 12VDC (or less) input voltage, with minimal current draw (1A or less)
  • Normally closed
  • Low heat output - can stay open for extended periods (hours)
  • very inexpensive - less than $10 each (preferably less than $5/ea)

Thanks for any insight! (Would this be a better question for the Engineering section?)


What you're looking for is called an "electronic proportional valve". And they cost at least 10 times what you are willing to pay.

Diaphragm valves are intrinsically "snap action". Once they get near to complete closure, the water pressure forces the valve completely closed. Proportional valves have no such bias, and as a result are not normally open or normally closed.


  • \$\begingroup\$ I was afraid that was the answer. What about a "Direct Acting" solenoid where the solenoid plunger itself controls the water flow, instead of using a diaphragm? \$\endgroup\$ Apr 19 '15 at 20:47
  • \$\begingroup\$ So it sounds like I'm back to looking into valves that can be actuated by servos... Do you know what types are easy to turn? Usually ball valves are very stiff - what about ceramic valves? Thanks \$\endgroup\$ Apr 19 '15 at 20:48
  • \$\begingroup\$ Sorry again, but you just won't find easy-to-turn valves for 100 psi. If there are any, they will be expensive. And high-torque servos aren't cheap either. You might get away with gearhead motors, though, if you can find a deal on some surplus units. \$\endgroup\$ Apr 19 '15 at 20:53
  • \$\begingroup\$ OK thanks for the insight. Back to the old drawing board... \$\endgroup\$ Apr 19 '15 at 20:56
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    \$\begingroup\$ @RyanGriggs - Huh. I wouldn't have thought it. Congrats on not taking my advice - I was wrong. \$\endgroup\$ Oct 2 '15 at 19:53

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