Question
QUESTION: I have a irrigation valve which will not open when the solenoid energizes.  I can coerce it open by either backing out the manual bleed valve or the solenoid half a turn. Altough, it will close when I snug them both back closed (Note: the solenoid seems to be still energized, I hear a slight hum from it)

I purchased a new solenoid and replaced the old one with no better results.  I was able to install this valve's solenoid in an adjacent valve, without disconnecting the wiring and the solenoid circuit from the bad valve operated it's neighboring valve just fine.  I took the neighboring valve's solenoid an installed it on the "problem valve" but this did not resolve the problem.

I opened the valve body and checked for blockages, dirt, etc.  The diaphram appears, to the untrained eye, as OK.  I made sure to reassemble the valve carefully to assure the solenoid bleed port was clear.  The valve does have a control knob, but I don't recall changing it.  

I'm out of ideas, can you help?

Thanks!
ANSWER: It sounds like the diaphragm needs to be changed but I need to know what type of valve it is and what do you mean by "control knob"? Please write back.

---------- FOLLOW-UP ----------

QUESTION: Not sure of the valve manufacturer.

The knob, probably for flow control, is located on top of the conical upper half of the valve which houses the diaphragm spring.  It is approx. 1/2" in diameter and has flat sides on the upper 3/4 of it's height. Inside of the valve there is a straight stainless steel wire which appears to be connected to the control knob stem. When the upper half of the valve is assembled to the lower half, this wire passes axially through the valve spring and extends through a hole in the diaphragm.

BTW, would you please explain the purpose of this wire?

Answer
The "wire" is a valve stem. You use it to manually open the valve. When the valve is assembled, turn the flow control knob all the way open and then back it down two turns (sometimes they stick). If that doesn't work then you must replace the diaphragm or the valve itself. I hope this has helped!