Zone valve question

[TommyCee]

Hello. I am new to this forum so here's 1st post. I have a Honeywell zone valve (8043E). I have spent time trying to understand exactly how this valve works, and I am pretty close except for one thing: the motor. When the T-stat makes, that causes the slow-motion motor top turn which opens the valve. Eventually, when fully open, a tang presses the end switch to turn on the circ. pump and ignite the boiler (via red wire circuit). While the T-stat is still closed (because we're heating), something caused the motor to stop. What is this mechanism?

I have never seen this explained anywhere.

 

[Stuff]

From the manual:

Automatic Operation
On a call for heat by the zone thermostat,
the valve opens and its auxiliary switch
contacts make, closing the circuit to the
system circulator. In a multizone system with
all the valve auxiliary switches wired in
parallel, any zone calling for heat can operate
the circulator. When the call for heat ends, the
valve closes by integral spring return. The
auxiliary switch contacts break the circulator
circuit.
Manual Operation
The motorized valve can be opened
manually by lifting the manual opening lever
over the stop and pushing slowly and firmly to
the MAN. OPEN position. The stop permits
the valve to be locked in the open position.
The valve returns to automatic position when
the valve is energized.

 

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[TommyCee]

Stuff: I have read this passage (or certainly one like it). It doesn't explain what causes the motor to cease rotating once the valve is open.
It's not the T-stat circuit as it remains closed until the set point is reached. I can't imagine it is controlled in any way by the end switch as the only electrical connectons to the motor are the 2 yellow leads that connect to the T-stat circuit.

 

[Stuff]

Not sure what you are seeing. The motor starts when the thermostat gives it power. It turns the valve 90º to open which stops at the limit (a physical stop). At that point the motor is still trying to turn the valve further but can't. When the thermostat stops providing power a spring action pushes the valve back to close it.

Gray has some good videos: A take-apart of an older version:

 

[TommyCee]

Stuff:
You wrote:
"At that point the motor is still trying to turn the valve further but can't."

But can't? As in it stalls? When the motor is isolated and 24VAC is applied, it will run until the cows come home. I have tested this. Your reply seems to imply that somehow when the motor encounters the resistance at the end of the valve rotation to the open position, it simply stops "magically". This is not so. When the isolated motor is running, I have grabbed the brass gear and applied resistance. It does not stop; it continues to run.

I appreciate your posting Gray's video; I had already seen it. If you review the video carefully, he never explains mechanistically that causes the motor to stop turning at the valve open position. He seems to imply that it's somehow related to the end switch, but - as I explained before - the end switch circuitry is completely isolated from the motor circuit.

I do not believe in magic; I believe there is a mechanistic explanation for everything that happens.
So I ask again: What specifically causes the motor to stop running at the end of the valve open arc?

I am not trying to be contentious here - I'm just looking for a straight, credible answer.

 

[TommyCee]

OK ... in further researching this, I stumbled onto this post, which presents the same question:
https://www.doityourself.com/forum/...4188-zone-valve-motor-constantly-running.html

According to NJT and PJmax, it IS resistance that causes the motor to stall, and hence stop turning. As a design issue, this blows my mind. Having been around electric motors for many years, it strikes me that any design that would exploit inertial resistance to stop a motor would eventually burn up the windings. Something tells me that there is an internal temperature microswitch that senses the added head from the stall, and internally disengages the power supply to stop the motor.

 

[Stuff]

It is a motor designed to be stalled. Low torque. When stalled it functions as an electromagnet providing a constant force to keep the gears from reversing and closing the valve.

Design issue maybe. It is common for them to fail. Probably why they sell the motors by themselves.

Spec sheet that mentions the Synchron valve motor stall capability: https://www.hansen-motor.com/product/ac/600Series-C-mount/

Motor speeds of 1 RPM and faster
can be stalled without electrical or
mechanical damage (as long as
voltage supply is to spec)

 

[TommyCee]

Thanks for your additional input Stuff.

I did something this morning I should have done 2 weeks ago: I called Hansen Motor Co., manufacturer of the Synchron motor in question here. I spoke with an engineer and learned more than I ever really wanted to know. What I learned was consistent with most everything posted here, but I thought I’d present it anyhow.

Hansen's Synchron motor is a hysteresis motor, or more accurately, a hysteresis synchronous motor.

These motors are very different in design from an induction motor with which I am most familiar. These motors are used where exact speed (assuming an exact-frequency AC source) and rotation with low flutter (high-frequency variation in speed) are essential. Their distinguishing feature is their rotor, which is a smooth cylinder of a magnetic alloy that stays magnetized, but can be demagnetized fairly easily as well as re-magnetized with poles in a new location. Hysteresis refers to how the magnetic flux in the metal lags behind the external magnetizing force. The angular lag between the rotor pole and he stator pole produces the hysteresis torque. These motors have a stator like those of capacitor-run squirrel-cage induction motors. On startup, when slip decreases sufficiently, the rotor becomes magnetized by the stator's field, and the poles stay in place. The motor then runs at synchronous speed as if the rotor were a permanent magnet. When stopped and restarted, the poles are likely to form at different locations. For a given design, torque at synchronous speed is only relatively modest, and the motor can run at below synchronous speed. In simple words, it is lagging magnetic field behind magnetic flux.

Design features of the hysteresis motor lend themselves to the stalling mechanism used in a zone valve application. When the zone valve rotates to its physical stop at the open position, the motor simply stalls with current still applied. This condition generates a bit of heat but not enough to be detrimental to the motor, which is typically rated at tens of thousands of open/close cycles before failure.

Here are several useful links that explain the principle and workings of the hysteresis motor:

https://www.electrical4u.com/hysteresis-motor/
https://circuitglobe.com/hysteresis-motor.html
https://en.wikipedia.org/wiki/Synchronous_motor

 

[Stuff]

You really were curious if you called the company.

So you still don't believe in magic? If you dig deep enough electromagnetic fields and waves are magical.