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About the Matco Norca AVA 125 air vent.

I have 3 radiators on the 1st floor, all different sizes, but all have the Matco Norca AVA 125 vent on them. The only spec I can find on this valve, other than dimensions, is 10psi. What does that mean?!? How does this compare to, say, the Gorton vents?
The 3 radiators I mentioned are a 3-Column/8 section/38"H, a 5-tube/7sec/36"H, and a 5-tube/4sec/36"H.
Based on Dan's book and all, all 3 of these radiators can't really be served by the same vent.
This is all strictly academic I supposed as I should just get rid of these $5 vents in any case.
Thanks in advance.


  • Fred
    Fred Member Posts: 8,541
    I don't know what those vents are??? Is this a 1 or two pipe steam system? The 10PSI means "10 Pounds of pressure per square Inch". This typically is the upper operating range of the valve but most newer vents have an upper range of 3PSI and even that is above the normal operating range of a typical residential steam system which should be no more than 1.5PSI. Are those actually vents or are they a bleed valve of some sort for a hot water radiator?
    If this is a 1 pipe steam system, I would try a hoffman 1A adjustable vent or one of the gorton slower venting radiator vent on each radiator. Is the vent tapping in the side of the radiator a 1/8" tapping for a standard vent?
    Do those radiators heat Ok now?
  • Mark N
    Mark N Member Posts: 1,094
    It is a steam vent. The 10PSI is the operating or drop away pressure. It is the pressure that the float in the vent will drop away after the first heating cycle. Explained on pages 106 and 107 in "The Lost Art of Steam Heat".
  • cooltoff
    cooltoff Member Posts: 9
    Hello Fred,
    Here's the link to the Matco Norca product page for these vents.
    They are listed as steam air vents.

    And my question was, how does this spec or "rating" of 10psi compare this vent in relation to the Gorton vent. You have answered that part, I think, when you say that a typical vent's range in only to about 3psi.

    This is a 1-pipe system. Yes, these are currently installed on the side where they should be, with 1/8" tap.

    This all began because after a recent servicing, things were not as they were. Major water hammer, frequent cycling and the vent in the hallway radiator leaking every cycle.
    And not knowing anything about heating I decided to get Dan's book to get some understanding of what was and is happening down there.
    So, after checking the pressure, which was set at 6psi with the diff. set to 3, and the water level, which was filling the sight glass, I set the Pressuretrol, as Dan stated, .5-in/1 diff, and lowered the water level to 2/3 in the glass, which got rid of all the above.
    This has prompted me to audit the whole system, starting with the main air vents and radiator vents.

    That leaking vent I mentioned above is one of these Matco Norca's and I'm trying to figure out what to replace it with.
  • Mark N
    Mark N Member Posts: 1,094
    The drop away pressure is the pressure at which the weight of the float is able to overcome the closing force of the system pressure. The faster the venting rate of a vent is the lower its drop away pressure is.
  • Fred
    Fred Member Posts: 8,541
    I just reread that. Page 108 also explains Drop away pressure a little better. Thanks Mark!
  • cooltoff
    cooltoff Member Posts: 9
    Oookay. So at 10psi does that make this a slow venting vent?
  • Mark N
    Mark N Member Posts: 1,094
    You're welcome, lots of great info in that book.
  • ChrisJ
    ChrisJ Member Posts: 14,969
    Steamhead said:

    Also the same as the ones they sell at Home Depot. I've seen quite a few that split down the side. If you need a direct replacement, try a Hoffman #40 or a Gorton #5, which is a bit faster than the H-40. For a good adjustable vent, use a Vent-Rite #1.

    One of the USAV vents that the previous owner had on all of the radiators here was split right down the side.

    I'm guessing USAV is the same as well? I think that may be what Homer sells but I'm not sure.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment