In reply to message posted by PlumBob:
Oh man this is going to be very intreasting.
Ok Sylvan he just opened the door
Wow what faith my public has.
Great Question and hopefully I wont disappoint Bob .
You know one of the most challenging jobs I have ever held was the position of licensed stationary engineer.
This was one of the fields that if you lived to be a thousand years old you couldn’t even scratch the surface in what is really required for this position.
Between HVAC compressor – condencer – metering devices and evaporator and reciever (bigger units)plus all the electronics – electric and mechanic’s involved it was a never ending challenge, so I took the easiest path out and became a “plumber”.
Ok now for the valve question being a plumber is easy as all we do is go to a supply house and ask the guy behind the counter for either a ball valve or a “speedy valve” or gas valve (cock) and let them pick it out.
Today’s non licensed stumblebums found a home in plummin and heatin BUT as a licensed professional stationary engineer we had to know which valves for various applications were to be used as someone should know.
So here is what I do remember from the various tests I had taken to be a “qualified” SE
The arrow on the valve most lightly means your talking about a globe valve.
A globe valve is used for throttling as opposed to a “gate” valve which is for positive shut off.
So far this is very basic.
Now considering you already are an assistant stationary engineer your already way above the average non licensed plumber when it comes to marketable skills.
So I can get slightly more technical as normally I have to tone down my answers to a 3rd grade mentality.
I had a conversation with Dan Holohan the heating Guru I asked questions from.
During one conversation I told Dan that on certain applications I did install a globe type of valves “backwards”
The reason I did was as follows.
For a positive shut off a gate valve is the way to go
The problem with a gate valve under certain conditions the resistance such as high head pressure against the gate are a major problem.
Lets take a normal 6″ or 8″ fire stand pipe 110 ft high.
Ok the “Force” on this gate on an 8″ pipe would hover around 2,400 PSI Not very easily to open huh?
Plumbers confuse static pressure with force all the time.
The “static” pressure would be only around 48 PSI as an real craftman you understand the concept.
Every try to open a steam valve with 125 # on one side? tough job
That is why on the larger “gave Valves” we use a by pass built into the valve.
The 3/4″ tappings allows for the use of a few nipples a union and a “globe valve” to by pass the gate so pressure can be equilized.
Once the pressure is about the same on both sides of the gate then the valve can be easily opened without the use of a crows foot ( Let the stumblebums think about this one).
Now one of the problems associated with a globe they can seep steam or other high pressure substances as the pressure is constantly pushing UP against the valve stem/ retaining ring this is why they are easy to open even with higher pressures.
By installing this valve backwards the pressure is pushing down on the valve disc thus insuring a more positive seal BUT in time it can do damage to the actual stem.
Globe valves are used for applications like under a faucet or toilet where the water volume can be excessive and spash so you throttle down the volume with this kind of valve.
Steam stations step down etc. use a type of globe valve like Leslie with pnumatics to open and close them.
The other types of valves for balancing like on an air handler application are normally designed like what a plumber would call a gas cock as the washer on the globe will wear out over time and the balancing valves can last for years and years as we know the velocity is always low unlike steam other wise the heating and cooling coils wouldnt last 6 months from erosion.
Please do not fall into the trap of the monrons who use a ball valve for a “fits all application” as it also has many draw backs.
Please feel free to contact me as I enjoy talking to professionals as that is how we learn from one another.
Hey if you ever feel like you want to give your brain a rest become a plumber