Re: Definition and function of a vacuum breaker

You can doubt the manufacturers all you want. This valve performs a
dual function. I doubt machine owners want to stand around and bleed
air while their machine heats. This is a problem that generates
service calls, that fortunately can be fixed over the phone.
The Cimbali Supers use the steam solenoid and a vacuum breaker to
release air during fireup.The vacuum breaker is the backup. I doubt
the engineers would have developed such a system if it wasn't
important to let the air out
A machine I worked on Friday had this problem. It had disabled itself
because the flowmeter sensed no water movement.I fixed that. Because
the vacuum breaker was stuck in the closed position, air pressure
developed which pegged the steam pressure guage. This kind of pressure
is not good for the pressurestat diaphragm and can exacerbate leaks in
the steam system. Not to mention breaking the guage.
The number one you refer to was conversational as in holding up a
finger when speaking, not necessariily designating air removal as the
primary function of the valve.
Come to think of it, why don't we just open the steam wands when we
turn the machine off, to prevent implosion? Why have a vacuum breaker
at all?....al


On Sun, 8 Jan 2006 17:58:11 +1300, "Rob van Loenhout"
<wontwork@xxxxxxxxxxxxxx> wrote:

>The "number one" function of the vacuum breaker valve is to break the vacuum
>and stop a possible implosion as you described. I doubt the manufacturers
>would bother putting a valve in when the steam wand does a fine job of
>expelling the air in the "false pressure" scenario.
>If the valve was designed primarily to let the air out then it doesn't do a
>very good job of that.
>
>Even a 20 ton capacity railway tank, made from 1/2" steel will implode if
>the covers are bolted down on a hot day and it cools overnite. IIRC someone
>posted a link to a pic of an imploded railway tank a few years ago.
>
>Far be it for me to correct you on anything technical relating to espresso
>machines.
>
>Rob "Pedant" vL
>
>
>
>"sprsso" <acritzer@xxxxxxxxxx> wrote in message
>news:oel0s11da0gejh0ap7eatr77ti71k4mn0q@xxxxxxxxxx
>> For those newer to this group, there seems to be some confusion about
>> the function of the vacuum breaker, so I will try to define it so that
>> the intended function of this device is simplified.
>> Vacuum breakers are almost always a threaded-in fitting with a piston
>> with an o-ring at the bottom of the piston. Sometimes they are a
>> teflon coated piston designed to fit against a concave teflon gasket
>> in a fitting that contains both. It is always mounted on top of the
>> boiler, and is purely mechanical.
>> The function of the vacuum breaker is, number one, to allow for the
>> expulsion of air heated by the expansion of water in the boiler to
>> allow for steam development. Steam and air cannot effectively exist in
>> the same pressurized environment as to be effective in an espresso
>> machine. As the air is heated and expands, it is exhausted through
>> this valve until steam pressure accumulates to the point that it
>> closes this valve, and allows steam pressure to develop until the
>> pressurestat or other regulating device determines that the
>> appropriate steam or temperature level has been achieved.
>> Two failure levels exist with this device. One is that the valve is
>> stuck in the closed position, where the pressurestat mistakenly
>> interprets expanded air pressuire as steam development and interrupts
>> electrical flow to the element. This is what is widely described here
>> as false pressue. Sigh. The pressure is not false, it is just air
>> pressure as opposed to steam pressure. It is not the desired pressure.
>> Reaeasing the air pressure, as described in another post will allow
>> steam pressure to develop. It, however, is not necessary to release
>> the air pressure over and over again. With experience, one will know
>> when stream pressure has developed.
>> An equal but much less discussed function of this valve is to allow
>> the safe decompression of the boiler as it cools when the machine is
>> turned off.
>> As the boiler cools, along with all accompanying tubing, a vacuum is
>> created that exists throughout the machine. The vacuum breaker at a
>> certain pressure level is designed to open to allow air back into the
>> system to equalize the pressures that naturally occur during
>> contraction during cooling. The contraction is severe enough with some
>> of the more poorly constructed machines as to cause boiler implosion
>> and line failure when the vacuum valve fails.
>> False pressure is a failure symptom of a vacuum valve, not a
>> definition of the valve.
>> To label a vacuum breaker as a false pressure valve is a misnomer. It
>> probably shouldn't bother me as much as it does, but it does....al
>

.

Relevant Pages

  • Re: Definition and function of a vacuum breaker
    ... The "number one" function of the vacuum breaker valve is to break the vacuum ... expelling the air in the "false pressure" scenario. ...
    (alt.coffee)
  • Re: Furnace saga continues
    ... isolated and I put about 22 pounds of compressed air into it. ... The expansion tank is brand new and was installed after this pressure ... The auto feed valve is closed and has always been ... I can isolate another loop but I'm ...
    (alt.home.repair)
  • Re: Definition and function of a vacuum breaker
    ... things fail the whole vacuum breaker valve should be replaced. ... There are generic replacements ... The vacuum breaker valve is a very simple part and there isn't really ... and allows steam pressure to develop until the ...
    (alt.coffee)
  • Re: Furnace saga continues
    ... isolated and I put about 22 pounds of compressed air into it. ... Your connectors or your valve may have a leak also. ... The expansion tank is brand new and was installed after this pressure ... I can isolate another loop but I'm ...
    (alt.home.repair)
  • Re: Definition and function of a vacuum breaker
    ... The Cimbali Supers use the steam solenoid and a vacuum breaker to release air during fireup.The vacuum breaker is the backup. ... Because the vacuum breaker was stuck in the closed position, air pressure developed which pegged the steam pressure guage. ... The number one you refer to was conversational as in holding up a finger when speaking, not necessariily designating air removal as the primary function of the valve. ...
    (alt.coffee)