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Rookie needs help w/ 2 pipe system

ernie_3 Member Posts: 191
First off it helps to know that w' 2 ppe vapor-vac systems, we're all rookies. not many living men who installed them but a whole bunch servicing them. Yes there should be a main vent or vacuum breaker, Hoffman 75 or 76. Should be near the end of the dry return (parallel) to your main, near the boiler. This will at least encourage the steam
around the main. The partially clogged wet returns need to be addressed. This is key to the system working properly. Ernie


  • Jim_28
    Jim_28 Member Posts: 3
    is my 2 pipe system missing parts?

    Hello every one - I need help.
    I have recently come into managing a bldg with several heating issues which, after trying to solve, lead me to wonder if I'm missing parts on the system. I have what I believe to be a 2 pipe gravity wet return system.
    From the boiler there is a dry return that parallels the main. The main has 4 legs that feed different parts of the building, each w/ a parallel dry return. At the end of each leg, there is a cross over steam trap between the main and return and they each drop down into the wet return. The condensate heads back to the boiler via gravity -- no pumps. All radiators have steam traps.
    Now the problem is, some radiators just barely get warm. I know that all pipes to the problem rads. pitch enough to drain condensate. I have replaced steam traps and I know that my condensate line is some what clogged, however, shouldn't there also be some type of venting system to get the air out so the steam can move? I can find none. After reading Dan's book it seems there needs to be something - a vent or air eliminator.
    I have had 4 heating pros look at the problem, and every time they take a look at those cross over traps they get a little puzzeled. They also can't answer my question on how steam should move through the system.
    Today when I blew down the low water cut-offs, a vacuum had developed in the boiler, air was sucked into the drain pipe before any water flushed out.
    It sure seems something's missing.
    Thanks in advance for any and all help! I will try to attach some pix's but if I'm un-succesful there is a picture on page 238 of "The Lost Art..." which shows my steam trap (or one like it).
  • Steamhead
    Steamhead Member Posts: 16,827
    Venting that Vapor system

    is done in two stages:

    1. Steam mains- currently handled thru those crossover traps which route the air into the dry return. Measure the length and diameter of each stgeam main and tell us what trap is on it. It's possible the crossover traps are not big enough to vent the mains as quickly as needed with oil or gas firing. The mains need to fill with steam in about a minute after the boiler starts sending steam to the system.

    2. Dry Returns- all traps in the system route their air into the dry return. You need some high-capacity venting to take care of all this air. Many times there is an air eliminator trap in the piping above or near the boiler. If more venting is needed I'd use at least one Gorton #2.

    Once the venting and wet-return issues are handled, that system should heat quickly and efficiently.

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