Steam Line Restrictions

Owen

Do steam line restrictions make 2# steam pressure impossible? I have many lines that have been improperly installed to begin with as well as knuckleheaded after.

The already too small run-out steam lines (from the correctly sized mains to the fan/coil units) were reduced even more a couple of years ago to allow installation of DDC controlled valves that i think are too small also. I asked the installer why they were using valves that size (1/2" to 3/4") and he replied that the bigger ones were expensive (I assume he meant more so than they had allowed for in their bid). I hope to replace many of the run-out lines as time and a pinched budget will allow but the valves will have to stay. If I minimize the length of the restriction, will that suffice to allow for lower pressure?

In the attached photos the steam line was reduced from 1-1/2" to 1/2" (who knows why 1/2") and the restriction was about 10" long. I removed the 1/2" portion and shortened the 3/4" section to about 5". (Photos 1 & 2)

Photos #3 & 4 show the typical piping arrangement in this section of the building (#4 is looking down). Note the use of bushings and concentric reducers There are about a dozen F/C units.

Is it hopeless?

SWEI

valve sizing

Properly specified control valves are sized by their CV, which is matched to the emitter and load -- so the body of the valve can sometimes be smaller than the diameter of the lines which are connected to it.



Did your DDC contractor provide any drawings?

Owen

Q & A

Question: remind me, CV?



Answer: no drawings on this one that I'm aware of.

SWEI

Valve Cv

Long version http://en.wikipedia.org/wiki/Flow_coefficient and http://www.engineeringtoolbox.com/control-valve-authority-d_1066.html



Short version, for North America:  Cv is the flow rate in gallons per minute at which the valve creates a 1 PSI pressure drop.

icesailor

Stupid question:

Is the CV you speak about for only water or is it for steam too? I mean, I know it is the same but if the supply is 1 1/2" and reduced to 1/2", is there a difference between steam flow and water flow?

Is steam considered different that water?

If one of those heaters is connected as 1 1/2" on the supply side of steam, it would swwn that that is a significant reduction in flow and energy.

Just learning.

Owen

That's My Question Exactly

Does steam behave differently through a restriction than water? A restriction on a water line reduces the VOLUME, no? No more water is going to go through a 1" -1/2"- 1"

line than if it were 1/2" the whole way.



But steam is a GAS! Doesn't that make a difference? I slips through only reduced by an amount (of pressure, latent heat, whatever) not as large as water would be. Therefore it is not reduced by the same factor. I hope.

SWEI

physics

At a given point on the pump curve, far more water will flow through a 1" system with a single short 1/2" restriction that will flow through a similar length of 1/2" pipe.



Steam has a specific gravity just like water does http://www.engineeringtoolbox.com/flow-coefficients-d_277.html

Owen

How It Should Be

This is the "Fresh Air Unit Schedule" The Specification that, as part of the Bid Documents which the Mechanical Contractor was legally bound to follow upon signing the Contract with the Owner. THAT'S HOW IT WORKS. It's called Contracting for a reason.



If you don't follow the Spec., your fanny is hanging out a mile...for one year.

Well, these guys got away with a combination of incompetence, dereliction and fraud.

Nobody was watching the store.



Compare Spec for F/A #1: Unit Steam Piping/ Supply & C.R. and photo #3.

(Repeated here from above post.)



This is just a sample.

SWEI

yikes

That second photo looks suspiciously like a rather unhealthy piping restriction directly attached to the output of that boiler.  It almost certainly violates whatever manufacturer's installation guidelines applied at the time.



However, a reduced control valve body size is not in and of itself an indication of malfeasance.

Owen

Uh...

The hulk on the leftt is not the boiler. It's a Fan/Coil unit. Sorry.

Steam is going in, not coming out.

icesailor

Fan Coils:

If it was piped full sized to the restriction/valve, the pressure drop and volume wouldn't be that high. But with all that 1/2" piping, there is  HUGE restriction and drop in flow.

With ejector water pumps, the piping is all 1 1/4" to the pump on the suction end. The water goes through a nozzle where the velocity increases and then flows through a nozzle. The space between the nozzle and venturi creates the suction which pulls the water from the well. It is said that for every 4 gallons of water that goes through the nozzle, 5 gallons comes out the venturi. But if four gallons try too go through the nozzle, I don't think that four gallons come out of the nozzle because of the restriction.

I'm not an authority on this but I have heard that if you find a discrepancy in a plan that is out to bid, there is often some item inserted in the bid specs that you are supposed to point out any deficiencies to the person having authority. That if there is a mistake, you should file some exception and point out the problem so the Suits can't say you are incompetent. And the designer will surely not ever come to your aid if it doesn't work.

SWEI

oops

My bad -- I'm used to smaller fan coils.