Orifice plates and condensate in supply risers

sscanley · September 2017

I am troubleshooting in an apartment complex with vacuum return. In 2012 thermostatic radiator valves (TRV) with orifice plates were installed. There are complaints of banging throughout the complex. The three buildings built in 1953 do not have drips on the supply risers. When orifice plates are installed, is more condensate produced in the supply risers, so that drip traps at the base of the supply risers becomes necessary?

EBEBRATT-Ed · September 2017

when you say supply risers I am assuming you mean a vertical riser that feeds several floors. Those I would think should be dripped.

If it's a supply going up to feed one radiator it shouldn't have to be dripped

Pumpguy · September 2017

Can you tell us what is the steam supply pressure?

The higher the pressure, the higher the mass of steam. With orifices limiting the amount of steam entering the rads, higher pressure steam would leave more in the risers.

If over 2 PSI, or maybe even less, I would try lowering the steam pressure and see if that affects the banging problem.

Jamie Hall · September 2017

But the short answer is yes. Think about it. Condensate will collect on the sides of the riser, not the middle. The hole in the orifice plate is in the middle. Presto, puddle. Puddle gets big enough and blocks orifice. Bang... The orifices will also cause more condensate -- maybe a lot more.

Why, might I ask, are the orifices there? With TRVs, they shouldn't be necessary...

JUGHNE · October 2017

Was the hammer there before the TRV's were added?
Are the orifice plates installed with the TRV's on the horizontal feed to each rad?
If so I am trying to understand Jamie's theory of the orifice covered with condensate?
And they will cause more condensate....I assume in the vertical riser as less steam is delivered.

I just walked in the door from a schoolhouse that has steam in it's return line. Rad traps bad. My suggestion to owners will be to add orifices to valves, (most are TRV"S) to keep steam out of return. The next solution would be chase rad traps to change out elements as needed. The orifices would be less money and prevent overheating which is common in a 1930's schoolhouse.
This building has express risers to high ceiling and downfeed steam lines. The 2 main risers are dripped into F&T's. One I just changed and the other has a cold pipe from the drip leg to the F&T, which I assume the drip leg is plugged.

With the OP vacuum return, will the rad be in a vacuum until the TRV opens? Then if the TRV closes will a vacuum again present itself. With the cycling of the TRV would the steam rush into the vacuum rad and create the water hammer?
Assuming the orifice is immediately after the TRV, to me it would be the same as the TRV throttled down to lesser flow of steam.

Yes, it seems the main risers should be dripped also.

sscanley · October 2017

Hello EBEBRATT-Ed
Yes, the risers serve 15 floors. Apparently the original vacuum return design worked without drips on the risers. But now there are a number of conditions that may be causing banging. One is the addition of TRVs and orifices. The building staff a relatively new. No one was at the complex for the heating work that provided the TRVs and orifices, much less before that. So comparisons are difficult. It does look like drips on the supply risers are required. Thanks.

Hello Pumpguy,
I will have to find out the operating pressure. But the pressure to the radiators changes, because each building has a modulating steam control valve controlled by a HeatTimer SRC (designed for vacuum operation) that changes the percent open as a function of the curve that is chosen. So the colder the day, the more open the valve, the higher the pressure and the more mass of steam in the risers. Thank you. We will have to look at lowering the pressure. Hopefully the more improvements that we make on the vacuum return side, the more we can lower the supply pressure.

Hello Jamie,
The orifice plates are in the inlet of the TRVs. So if the valve is horizontal (some are angle) and the runout has become pitched toward the valve, yes, puddle and bang. If the pitch is correct, back to the riser, the condensate goes down the riser. But still, without a drip, yes, banging. Thank you. The TRVs and orifice plates were put in for energy conservation using incentives from the New York State Energy Authority (NYSERDA). But the consultant made a point of stating that without the orifice plates, all radiator traps should be changed every three years. So the orifice plates are helpful for us, because they limit the steam and condensate in the returns.

Hello JUGHNE,
We do not know when the banging started. It has been said that the banging got worse with the installation of TRVs and orifices. But it happens that replacing the trap, or fixing the pitch or unclogging the return sometimes stops the banging. See my response to Jamie above regarding the configuration of the components at the radiator and puddling. I am still trying to sort out the scenarios of steam rushing into the vacuum. But I think on the off cycle the pressures on the steam side and the vacuum side equalize, because the vacuum pump is off. At the beginning of the cycle the vacuum pulls out any air or moisture and helps the steam fill the system, because mostly the traps are cool and open and the TRVs are calling because it is the beginning of the cycle. Also there are no orifice plates on the top floor radiators which helps the steam fill the whole system quickly.

JUGHNE · October 2017

I have never seen a vacuum steam system.
I assume the vacuum is pulled on the return lines only?
If so then all air must be pulled thru TRV and orifice?
IIRC I believe I read that vacuum systems could use smaller pipe sizes.

Just a brain storm here (or maybe a brain fart).
Before the TRV and orifice would the steam have traveled quick enough up the risers to have little condensation drip back down.
Now it lingers (and perhaps condenses) in the risers without getting quickly into the Rads?? Just thinking out loud.

Is the system still insulated?

Scott.Malo · October 2017

Hi Guys! Scott Malo here from Tunstall Corporation. I am the Director of Energy Solutions and saw this post. I was curious to know if this is a project that we participated on and if so, was there any way we could help. sscanley, where is your building located?

EBEBRATT-Ed · October 2017

I think @JUGHNE is probably making a good guess. Possibly there is condensate collecting in the supply risers due to the TRVs & orfices.

I have an excellent booklet from Nash/Jennings on a steam vacuum system. If I can find it & figure out how to scan it it would be a good add to the library

The Steam Whisperer · October 2017

Did they drip the supply risers through the bottom radiator supply valves? I see that pretty often, so you can't use orifice plates or have the valves closed in those bottom radiators. In this case just adding a drip around the radiator supply valve and orifice into the radiator or radiator return will work. Several manufacturers used to make a combined radiator supply valve and trap assembly just for this purpose.

Jamie, the orifices, if properly sized and the system pressure properly controlled, eliminate the need for radiator traps. In addition, they provide a high pressure drop right at the supply valve, so steam distributes through the building very evenly before starting to fill the radiators. The boiler capacity can be reduced to the heat loss of the building plus a small pick up factor, since the boiler no longer sees all the installed radiation, only the part that the orifice allows to be in use. I.E. We have a large home with 1800 sq ft of radiation and fire the system nearly the whole winter with only a 160,000 btu/hr output boiler and it heats quietly and evenly. There are lots of other things that can be done too to improve system performance once the orifices are in place.

Orifice plates and condensate in supply risers

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