In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Simple 2 Pipe Vacuum Setup
I got to thinking that some people might be thinking that my setup is complicated and expensive. It really is neither so I thought I would detail a possible simple starting place for any 2 piper interested in giving it a try.
You will need an delay on/off 24volt timer relay that has both the on time and the off time independently adjustable. I haven't looked in a while but I think you can do one of these for less than $100. By the way, the PLC I use is $129 which provides unlimited control options so this never gets very expensive. I don't have a model# handy at the moment for a timer relay but I will find that if needed. The output relay of this timer gets wired in series with the Tstat signal line going to the boiler. Once installed, it merely sets the actual burn time and off time (I call it wait time) to minutes of your choosing and keeps that regular pattern throughout the call for heat. With this being the only control device you will need to pick a cycle where the net total burn time % is enough that you know will heat the house on a really cold day. For me that is 50% so I would choose 10min on/ 10 min off which is 30 burn minutes per hour evenly spaced. You could make it 15 and 15 if you want only two cycles or 30/30 if you want only one. I ended up with 3 but nothing magic about that really. It doesn't have to fit evenly in hours either obviously. All up to you and kind of fun.
The above setup is where I started and ran several years. It merely spreads out the burn and cuts overshooting way down - especially if your boiler is oversized like mine. Its only real weakness is at startup where you really would like that first burn from room temperature piping to be a little longer. I have since installed a preheat sensor and my first burn is about 25 minutes. So the first hour with the above setup is a little slow but during times you actually need heat you don't need any preheats and the setup really improves everything after that. You also can just go to the device and easily change the on/off ratio anytime you like with the knobs on top. I highly recommend anyone interested in this at all spend $100 or probably less for one of these and start trying. It is too easy. Remember - these extra cycles are not bad and don't waste anything. Your system is not cycling on pressure because the boiler was never allowed to run long enough to build pressure or if it is something else is wrong.
Ok, on to vacuum. At this point I still had a vent on the end of the main at which I heard air going in and out of every cycle. As I thought about this I realized this air was just going in and out and wondered if that was really necessary. So I took it off one day just for the heck of it. Nothing changed really except that air now went in and out of the vent on the dry return. The rads seemed to heat just the same or maybe even a little better as air never actually got all the way back in the main anymore with the burner only off 10 minutes at a time. The startup cycle was still fine too. As I have pointed out there is plenty of time on that first warmup cycle for air to go out of the main through rads and out the dry return. At this point there were still a few vents on rads left around from previous contractors who didn't know what they were doing. By this time I had Dan's books and took them off. So then I had only one point where air was being allowed back in to the system when the burner went off and I wondered if that really needed to happen either. Well, I soon found that that didn't need to happen and the rest is history.
If you want to try this here is a simple start. I even have model numbers. You need one location on the dry return to install a 110V solenoid and an ultra low pressure switch. They need to be wired such that when the switch senses any pressure above atmospheric its contacts close and power the solenoid valve to open. This setup can be stand alone anywhere and does not need to be connected to anything at the boiler. When the burner goes off and the system begins to sink into vacuum, the switch contacts will open, the solenoid will close(obviously you need a normally closed one of these) and now your system is all closed up and air won't go back in. A vacuum gauge nearby to see the vacuum level will help. I use a Dwyer Cat# 1910-00 switch and an Alcon Valves Cat#UG86 solenoid. Both are a number of years old now - don't know current status. For whatever reason the 60" water vacuum this switch sees every cycle has never hurt it. Also, the solenoid valve must be put in with the flow arrow going out of the system. Won't seal against the vacuum the other way. Another thing, for safety I installed a simple check valve next to the solenoid in the event that the solenoid failed to open so no pressure could ever build in the system.
So there you have it. I probably missed something or have something backwards - just let me know. There really isn't a mountain to climb to give this a go. I have enhanced things quite a bit from here with PLC control but as I said before even that is not expensive nor is the programming complicated. Maybe there is no interest. That is ok too. I just wanted everyone to know that what I am doing is really simple actually. My steam is always going in forward motion to my rads during all calls for heat - always. No wasted effort chasing air back and forth. More even heating as mostly vacuum is pulling steam into rads more in response to what is needed rather than pressure pushing steam in based on vent location. I have found it to be a lot better and no vents to buy and maintain.