Zone Valves – A look Inside B&G’s Comfort-Trol Valve’s Operator

Electric Zone Valve
Another way to zone a hot water system is to use electric zone valves with a single circulator.

The zone valve takes the place of the Flo-Control valve. Each zone valve acts as a “Gatekeeper” to the zone it serves. The circulator provides the water, and the zone valve allows that water to either pass or not pass.

The operating sequence

To give you an understanding of how electric zone valves work, let’s take a look inside B&G’s Comfort-Trol valve’s operator.

First, the room thermostat calls for heat by sending an electrical “Go” signal to the zone valve’s operator. Inside the operator, the electricity flows through a normally closed switch and around a tightly wound coil called a heat motor. This wire has high resistance, so when the current flows through it, you get heat.

And heat is exactly what you want because the heat motor surrounds this bullet-like device called a power pill.

The power pill is filled with a temperature-sensitive wax that expands when the heat from the heat motor hits it. As the wax expands, it pushes a piston out of the power pill.

The piston pushes against the spring-loaded lever that normally holds the valve closed. This action lifts the valve disc off its seat and opens Comfort-Trol’s water valve.
Water now has access to the zone. But nothing is flowing because the circulator hasn’t yet been called on by Comfort-Trol’s operator. That’s about to happen, though, because the piston will keep pushing the lever forward until it trips an end switch.

The end switch makes a connection (through a relay) back to the circulator. The circulator instantly comes on and moves water through the Comfort-Trol water valve and out to the zone.
In systems without tankless coils or side-arm heaters, the end switch, working through the relay, would fire the burner at the same time it starts the circulator. Meanwhile, back at the Comfort-Trol operator, we have to have a way to shut the heat motor off, so we let the piston stretch out just a bit further until it breaks the heat motor switch.

That switch cuts power to the heat motor, and almost immediately, the wax in the power pill begins to cool and shrink. Naturally, as that happens, the spring-loaded lever arm pushes the piston back into the power pill.

The circulator, however, is still running while this is going on because the end switch is still closed. That means Comfort-Trol’s water valve is still open, and hot water is still flowing out to the zone.

The piston slides back a bit, just enough to allow that switch to close and send power to the heat motor again. The piston then goes back out again, the circulator continues to run, and the zone continues to get heat. Comfort-Trol’s piston keeps sliding back and forth as long as the thermostat calls for heat.

Taking control of water hammer noise

When the thermostat is finally satisfied, the power to the Comfort-Trol valve is cut. As the power pill cools, the piston is forced back by the spring-loaded lever arm. This breaks the end switch, sending a “Stop” signal to the circulator. Then the spring-loaded lever gently seats the Comfort-Trol valve, and water stops flowing through the zone. The slow closing action of the valve lessens the chance for water hammer shock when the valve finally seats.

Water hammer is a common problem with some electric zone valves that close too quickly. If two zone valves are calling at the same time and one shuts off, the circulator will continue to run. The valve now has the burden of seating against flowing water. If the valve can seat slowly, it will not bang. However, if the valve tries to close too quickly, it will hammer like a solenoid valve on a washing machine.

There are other types of zone valves on the market that work a bit differently than the Comfort-Trol. Some, for instance, use clock-type motors to open and close the valve. Others are power-driven open and power-driven closed. We chose the heat motor design for our Comfort-Trol zone valve because we believe this gives you the best combination of small size and quiet operation. We know that zone valves are not always installed in boiler rooms. Often, they’re installed inside the baseboard, right in the living space with your customer. Obviously, valve size and noise become very important when the valves are used in places such as this.

We wanted something that would work anywhere you decide to use it. That’s why we chose the heat motor design. Comfort-Trol fits where others often can’t.

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