Taco needs to create an animation of how the 570 series zone valve works.

@Steamhead 's comment just above is why if I'm going to play with electrics I ALWAS use both a non-contact and a contact type tester to verify that the circuit really is dead. I don't like shocks…

The thing is with @Steamhead's comment above and if you understand the 3 wire actuator circuit situation and you understand the 24 VAC in the heating equipment (the power for the T-T) may be bonded to ground in the heating equipment or Aquastat, etc., then the other 24 VAC power source for the thermostat and wax motor can NOT be bonded to ground, it needs to be 'Floating'. Or if it is bonded to ground it needs to be phased correctly and someone else can unknowingly easily screw that up.

An isolation relay or Multi Zone control boxes (Isolated X-X) does make whole ground bonding, either by mistake or intent irrelevant. Since it adds another layer of isolation to the overall circuit situation.

4 wire actuators by design provide the isolation.

That thing looks scary.

I once knew an old-timer electrician (this was back in the 1970s and he was an old-timer then) who told me that. I had run into an old fuse panel where the neutrals were fused as well as the hots. Back when electric wiring was first being installed, in order to get 120v you might have 60v on either side, just like today's 120/240v service where 120v on opposite sides makes 240v. It all depended on how the local grid was set up. In those days, you only had to break one side of a circuit like that to control a light or other load. Obviously Codes have come a long way since then.

That's really well done and captures the operation of the 570 series very well. Not much I can add other than a few quirky specifics. First off, the actual end switch is a normally closed switch and that little tab on the piston actually holds it open when the valve is closed. As the wax element pushed the piston down, the tab actually releases its hold on the end switch, allowing it to close the end switch circuit.

The description of the switch lifter on the other side of the piston is 100% accurate - and the fact that it opens and closes, causing the valve to oscillate, breaks the completed circuit on the power side. That does two things - it minimizes any worry of "cross talk," due to the fact the end switch and power circuits share terminal 2. Also, since it breaks power and makes the power draw intermittent, it's how we can put up to three of these babies on a 40 VA transformer, even though it the valve itself has an amp draw of 0.9A, or 21,6 VA. Since that draw is not continuous, you can easily put 3 on a 40VA transformer. The worst thing that will happen is that the valve action might slow down when two or three are all opening at the same time, which usually only happens on start up ur during testing.

To make things a little more interesting. I had a situation In a 30 unit building, Where I had to replace some 570s. But I had to use something where the direction of flow didn't matter. So, I used the Taco Sentry zone valves and Mario Silva from taco was good enough to send me the following diagram.