"If you can't explain it (vent dampers) simply, you don't understand it well enough." - A. Einstein

JohnNY

I'm having a hard time coming up with a simple explanation why a vent damper needs power to close. Seeing as the motors look identical, all my students want the damper to work exactly like a Honeywell zone valve.
There is no internal wiring diagram available online that I can find, nor is there one of those wonderful animations showing the process of making and breaking a call for heat.
As I understand it, the control board contains a SPDT switch that alternately energizes the parallel open-or-close circuits.
Any help explaining this functionality is appreciated.

Jon_blaney

It works like the window in your truck. One way open and the other way closed. No springs. Direction of current determines motor direction. The control board pushes the switch, controls the current flow.

JakeCK

Jon_blaney said:

It works like the window in your truck. One way open and the other way closed. No springs. Direction of current determines motor direction. The control board pushes the switch, controls the current flow.

I don't think that is 100% true. Someone feel free to correct me if I'm wrong but I'm pretty sure the vent damper on my boiler only rotates one direction. My gut tells me there are several reasons for the way it functions. One being the little metal tabs that actually make contact with vent walls. They're almost like brushes and have to point in the right direction so it can rotate and not jam up or make a god awful noise(worse then it already makes anyways). 

Larry Weingarten

Hi, I'll also add that it's a fail safe approach. You want it to be open should something go wrong. If it failed closed and the burner came on...

Yours, Larry

Steamhead

There have been several damper models over the years. The one we almost always see now was originally made by Effikal and is now a Field Controls product. The damper motor does not reverse on these models.

In this damper, the thermostat sends power to operate a relay (which IIRC is solid-state in current models). This starts the motor, which then rotates 90 degrees until the end switch operates, signifying the damper is open. This stops the motor and sends power to the gas train, and the boiler runs.

When the call for heat ends, the relay drops to its "off" position. This removes power to the gas train and starts the motor, which rotates 90 degrees until a second end switch operates, signifying the damper is closed. The boiler is now ready for its next call for heat.

For those not familiar, on Field and later Effikal dampers, if the power unit fails it can be replaced.

JohnNY

Steamhead said:

"...the end switch operates, signifying the damper is open. This stops the motor..."
The end switch stops the motor. Hard to wrap my head around that in a solid state device but give me a moment here to digest it.

When the call for heat ends, the relay drops to its "off" position. This removes power to the gas train and starts the motor, which rotates 90 degrees until a second end switch operates, signifying the damper is closed.
So, same function in what I would call a parallel circuit that turns the motor and closes the damper.

Thanks, Frank. I still wish Field would publish a wiring diagram somewhere though.

Steamhead

@JohnNY , as far as I know, the end switches are still mechanical.

EBEBRATT-Ed

most zone valves have a spring (but not all), when they get powered the overcome the spring and drive open, when power is removed, they spring closed

hot_rod

I think they work like those White Rogers  1361 zone valves that just rotate around, one direction rotation 

MikeAmann

@Steamhead - so you are saying that the motor turns in one direction only (OPEN), and stops rotation at 90 degrees when an end switch is made? Then do it again making another end switch (for CLOSED)?

MikeAmann

@JohnNY - I did some searching for you. See if this helps: https://manualmachine.com/fieldcontrols/46457800/1117750-user-manual/
And from an older thread: https://forum.heatinghelp.com/discussion/168382/flue-damper-wiring

JohnNY

MikeAmann said:

@JohnNY - I did some searching for you. See if this helps: https://manualmachine.com/fieldcontrols/46457800/1117750-user-manual/
And from an older thread: https://forum.heatinghelp.com/discussion/168382/flue-damper-wiring

Thank you! Very thoughtful of you. I'll look through this.

Steamhead

MikeAmann said:

@Steamhead - so you are saying that the motor turns in one direction only (OPEN), and stops rotation at 90 degrees when an end switch is made? Then do it again making another end switch (for CLOSED)?

Correct.

Zman

I could explain that simply now and could not before. This has been a good post, thank all who contributed. I wonder if they wired it that way and were a bit cryptic in their instructions to prevent folks from bypassing it.

TAG

I had one fail years ago in a house with two gas boilers. Buderus used Honeywell aquastats on the atmospheric boilers. One of the setups had the vent damper plugged directly to the aquastat with a special one way plug. The other was wired to a terminal block. Naturally the aquastat with spot for the plug was viewed to have failed and the service guy from the gas company did not have that aquastat on his truck. So he cut off the plug and tried to install a new aquastat and wire it up. Made a mess of it and the second guy was no help ... so these simple things have caused issues for years.

As others have said -- the motor only spins in one direction. The motor spins CCW when viewing from the cap. It rotates 90 degrees at each cycle. The motor has constant power to it and the control power feeds through the end switch to the ignition module. When the control drops off the ignition module is cut off .... not when the limit opens. That is how mine work. The bypass takes the control away from the motor I don't believe it does anything with the end switch or you could move the bypass and have the boiler fire with the vent closed. If the vent is closed and you move the bypass switch the motor moves the vent to open --- the boiler does not fire when fully open unless it gets a call to.

Mine ended up being the motor and nothing was wrong with the aquastat. I told the gas company to forget coming back. Effikal sent me a new head and with some pleading a new wire with plug. I switched out the aquastat. Not long after that issue there was a recall and they sent a new head for the other one and one I had at another place. Worked for 20 years and the spare aquastat is still on the shelf.

They also have a little plug that comes with the units .... the plug is for a hole in the damper if you don't have a pilot

EdTheHeaterMan

Zman said:

I could explain that simply now and could not before. This has been a good post, thank all who contributed. I wonder if they wired it that way and were a bit cryptic in their instructions to prevent folks from bypassing it.

You nailed it!

I remember when these things were first introduced in the 1970's. Some were "stupid proof" with 6 terminals.

1 & 2 were for power
3 & 4 is where you put the wires that powered the gas valve (removed from the gas valve)
5 & 6 were wired to the gas valve.

This was too easy to understand and lead to technicians putting the wires back on the gas valve and forgetting to make sure the damper was open or removed. Making them "UNstupid proof"

There was a 120 V. version for oil burners.

They also had power open spring closed models that proved to be problematic because they could close with no power and then some idiot would "FIX" the problem wiring and get the burner running with the damper closed.
Then they were redesigned to Power closed and Spring open, but that wiring was complicated and prone to failure.
The Field/Effikal model has proven to be the one with the least problem and the standard for the Molex wiring design.