Venting and System Cycling on Pressure

Roddy

Another main vent/timing, and pressure question: I've read a lot here and in Dan's books, but I'm probably forgetting a number of things. With that intro., my question is: Should main vents shut off as soon as steam hits them and should it be early in the cycle? (I think the answer is yes.). Does that mean that after the main vents close, then the radiators start or continue to fill up with steam and eventually the radiator vents shut also if the system continues to call for heat?

The reason I'm asking is my Pressuretrol and attached pressure gauge (it's in ounces, and shuts the system down at 28 ounces and kicks back in at 8 ounces ) only registers if/when I move my thermostat up a couple of degrees, so as to make my single pipe parallel flow steam system run longer. Only then does the system build enough pressure to make it cycle on and off on pressure, until reaching the desired thermostat / house temperature. On most days it only cycles on and off on temperature at the thermostat, i.e. it never shows pressure on the gauge nor does the Pressuretrol engage except on the coldest Chicago days of the winter. Is this acceptable / desireable? Should I change something (like adding more venting to the main vents)?

My system heats my two story, 2,000 sq. ft. home evenly and well, so I have no real comfort complaints. In the back of my mind I'm wondering if I'm still not venting my mains fast enough (3 of the smaller Gorton main vents on each of my two return loops), and maybe my radiator vents are acting as mains also.

Any thoughts? Thanks in advance.

Roddy in the Chicago burbs

Fred

All steam vents (main and/or rediator) should close when steam hits them. Proper main venting will reduce the amount of time the boiler runs, during a heating cycle, to push air out of the mains. Once the main vents close, the steam will then push into the radiator run-outs and then into the radiators, pushing air out of those, through the radiator vents.
Weather or not you have enough main vents is driven by the amount of air that needs to be evacuated. Calculate the volume of air in the mains (diameter of pipe X length X cubic feet of air per foot of pipe based on the diameter. Determine the venting capacity of the air vents at 1 ounce of pressure and go from there. Keep in mind that the total venting capacity of any and all main vents will be impacted by the size of the opening in the main that you mount the vent to. A 1/2 inch tapping will only vent at a the rate it can vent. ADDING MORE VENTS TO THAT PIPE WON'T MAKE THEM VENT ANY FASTER THAN THAT TAPPING WILL ALLOW.

EBEBRATT-Ed

In a residential system there is no need to build pressure. If the boiler heats the house without building pressure that is exactly what you want. If it heats in a reasonable time frame your venting is fine.

nicholas bonham-carter

Use a stopwatch to determine the time needed for steam to travel the length of the supply to the main vent.
Then remove the main vents, and repeat the test, and time it.
Make sure in both cases that the boiler is hot, and has recently steamed, so there is no heating up period to skew the results. Be ready to cut the power to the boiler the moment steam comes out of the vent trappings, as it can burn you severely.
If you have enough main venting, there will be very little difference in the time of steam arrival.—NBC

Jamie Hall

Bottom line. Sounds to me like you're just fine. Be happy.

Roddy

Got it. Thanks everyone. Happy Thanksgiving.
Roddy