Air vents on two pipe system

Mike Miller_2

Okay Guys, looking for a little bit of a different take on venting here. I am working on a system where all the first floor radiation is cast iron baseboard, and some upstairs radiation is also. This system was a mess when I first tied into it, re-did all near boiler piping with a drop header to dry the steam out as much as possible ect. the upshot has been a system that has heated well but has been noisy. I started looking again at the piping that had been changed in this system and two things pop out, first I found where an air vent had been removed and also the system is smaller than it used to be, piping and radiation removed. So thinking I was a real genuis I added an air vent back where the one had been taken out. Now the system was louder that it had been, and in places it had not been loud before. Now everything I have run in to information wise has leaned toward the faster you get the air out the better, but it could it be that I have a velocity problem through these baseboard units and if I reduce venting capacity I will slow this system down and fix my banging problem? And before you ask, I have verified that I am not trapping water anywhere, but these baseboard units are piped in and out on the same level and I think that they have a layer of condensate at the bottom of them exposed to steam every time this system fires up. Any help would be greatly appreciated, thanks Mike

Rod

Air Vents

Hi Mike - When you say a "two pipe system" do you have a trap on the baseboard or is it just a drip line?   With baseboard it is really easy for the condensate to get in the way of the incoming steam so it generally pays to slow down the venting. I use a Hoffman 41 on mine (a slow vent - between a 2 and 3 setting on a Hoffman 1A)  Does the banging only occur early in the steam cycle? Is there any pitch (slope) ?

- Rod

RJ_4

noise

Some of the old bldg's I worked at in San Fran.  had various types of pipe noises, after eliminating all the obvious problems, found the risers in these 90 year old bldg' were never insulated, this plus loose pipe supports was causing the problems. I did have to open up the walls to find the problem, The bldg owner was given a quote to correct the problem which was going to be quite a job. never heard back.

Mike Miller_2

Traps

These are trapped, first floor has the traps below the ceiling in the basement, the ones on the second floor have them right off the baseboard. I am glad to hear I might be on the right track. So I am talking about air vents on the mains in the boiler room. thanks Mike.

Mike Miller_2

Traps

These are trapped, first floor has the traps below the ceiling in the basement, the ones on the second floor have them right off the baseboard. I am glad to hear I might be on the right track. So I am talking about air vents on the mains in the boiler room. thanks Mike. This happens early in the cycle, just as the steam is arriving at the radiators, the radiators are level, all piping I can get to has correct pitch.

Jamie Hall

Are your air vents...

on the mains in boiler room, or on the dry returns? 



A number of two pipe systems were set up with the vents on the dry returns in the boiler room, and crossover traps from the mains to the dry returns at the ends of the mains.  If this is the case with your system, are those crossover traps working?  If they are, there is no need to vent the mains, just the dry returns.



And, of course you have to vent the dry returns in any case -- otherwise the air can't get out of the radiators.  But since they are working, that's not your problem.



If the racket is just as the steam is getting to the radiation, you can be almost certain that what it is is hammer (or slosh!) from that initial condensate in the riser being pushed along in front of the oncoming steam and making the noise.  Much slower venting on the dry returns might help -- but at the cost of much slower heat, as well.  On the other hand, if the runouts or the baseboards are long but pretty flat, it is just as likely that the problem can only be fixed by improving the drainage there.  The baseboards should be pitched to the traps, away from the inlet.  The runouts should be pitched to drain either way.

Mike Miller_2

vents

Jamie, these are vented on dry returns, two F & T at the end of two mains to accomodate getting condensate back to the dry return, and one crossover at the end of the closest steam main. I have tried every thing I could think of to stop this banging and all I can think of is that the orginal boiler, which was long gone by the time I saw this job would have had a bigger steam chest and this system had so many terrible things done to it that I have no idea of original venting. But slowing things down won't be a bad thing for this system. I put Hoffman 75H on those dry returns and that is just too fast, I have proven that to myself, so I am wanting to try a Hoffman 4 on the places I have to vent. Any feed back is appreciated, Thanks , Mike

Jamie Hall

Chances are...

that you have perfectly good nice dry steam; sounds as though you knew what you were doing with the near boiler piping!



Contrarian as it may sound, I suspect that slower venting will probably help with the noise.  Certainly is worth a try.  The problem with a longish near horizontal runout (I have one, and it bangs no matter what I do with it -- it being a situation where I can neither make it bigger nor change the pitch) or with baseboard is that the initial flow of steam quite naturally condenses -- and the subsequent steam whizzing along in there pushes that condensate happily along in front of it until it hits something.  Baseboard is much more prone to this problem, of course...



So do try the slower venting and see what happens.

gerry gill

maybe a couple things to look at

would be to lower the firing rate of the boiler to more gently send steam out..(you can always readjust so why not try), and another thing we have found was if the baseboard has a top inlet it seems to work much better to use that than the lower inlet..and also are the traps full size inlet or is there a bushing then the trap which would hold back water in the baseboard? just things to consider..