Hammering on the first evening run then disappear

tomsloancamp

I have a 1pipe steam system.I noticed that when the boiler fires up first during the event when the temperature drops after it not running all day I get hammering. Subsequent runs there is no hammering. The hammering is in the main line which runs through the basement. It has the correct pitch. I believe the water level was too high when first firing it and may have gotten water in the lines because I heard swishing sounds then hammering. I lowered the water level. Any advice is appreciated.

Hap_Hazzard

Check to see if your main is sagging. It could have the right end-to-end pitch but still trap water if it sags due to a bad hanger or sagging joist. You can either check the pitch at every couple of feet with a torpedo level or by shining a flashlight or laser pointer parallel with the pipe.

Fred

With the boiler not running all day, how long is it running to bring the house temp back to set point, in the evening? Anything more than 2 or 3 degree drop can be problematic. Having said that, How much water is in the boiler? If it's too high, still, it can cause wet steam which can create some hammer.
What pressure is the Pressuretrol set at? It should be set at 1 with a .5 Differential for a 1.5 Cut- Out. Make sure the pigtail (looped pipe the Pressuretrol is mounted on is not clogged. If it is, the Pressuretrol may not be able to see the system pressure and it may let the boiler run for an extended period of time (on the first evening cycle). That may allow the system to build enough pressure that condensate can not get back to the boiler, hence the sloshing you hear. Of Course all of this assumes you are correct about the pitch of the Mains and radiator run-outs.

tomsloancamp

It appears the pressuretroll is set higher then 1 (I’ve included a pic.) looks like above 2psi. I didn’t check the cut out yet. I set the water level half way up the glass tube... originally it was set 1 1/2 inch from top. Should the water leveL match the marking on the boiler side?

Fred

tomsloancamp said:

It appears the pressuretroll is set higher then 1 (I’ve included a pic.) looks like above 2psi. I didn’t check the cut out yet. I set the water level half way up the glass tube... originally it was set 1 1/2 inch from top. Should the water leveL match the marking on the boiler side?

Set the Cut-In on that Pressuretrol to the .5 (Bottom of the scale and set the white wheel inside the unit to "1" facing out. Water level should be half way up the sight glass, no more than 2/3's . depending on the boiler, but 1.5" from the top is too high.

kcopp

Boiler looks pretty new... was it ever Skimmed?

tomsloancamp

i don’t believe it was skimmed. I bought some piping and a valve and plan to skim it my next day off.

kcopp

That could throw wet steam up into the main. Especially on the 1st run.

Jamie Hall

The first run on a cold system usually will show up problems if they are there. As has been suggested, check all the piping for dips or sags -- it doesn't take much.

tomsloancamp

The lowering of the pressuretrol settings seemed to help. Will definitely skim the boiler. Thanks everyone for the advice!

Fred

Those Pressuretrols are notoriously out of calibration too. Even though you set it properly, it still may be running higher than it should. Here is the procedure to recalibrate it. There may be some red or blue locktite on the hex screw and it may not turn. If it is out of calibration, use a small soldering iron to melt the locktite, if the screw won't turn. You will need a 0-3 pressure gauge on the boiler to calibrate it. Below is a link to a gauge most of us use.
Inside the Pressuretrol, right below the micro switch, there is a pivot arm. At the end of that arm you will see a screw pin that is activated by the diaphragm at the bottom of the Pressuretrol. If you look very carefully at that screw pin, you will see it actually has a tiny (I mean tiny) hex head on it. It takes a .050 hex wrench and you can turn it clockwise (Towards the bottom of the Pressuretrol to decrease the Cut-out pressure or counter clockwise to increase the cut-out pressure (which none of us want to do but who knows, your Pressuretrol may be really screwed up!). Turn the power to the unit off first. You may find the first attempt to turn that screw a little bit stubborn (relatively speaking) because it has some Locktite on it but it does turn. Don't turn too much, a tiny fraction of a turn goes a long way towards getting it adjusted where you want it (maybe 1/32 inch turn to start with) . You may need to play with it to get it exactly where you want cut out to be.
https://www.pressureworx.com/product/low-pressure-gauge-25-0-3-psi

tomsloancamp

@Jamie Hall when I investigated the hammering more closely I I think it’s a sag in the main line. A section looks like it got rehung at some point I don’t know if it occur during installation of our new boiler or before. We had a pipe relocated because of a kitchen remodel last summer but the old boiler didn’t hammer. I can show pictures of the pipes if needed.

Jamie Hall

No picture needed. I can assure you -- from experience! -- that even a very small sag can cause hammering, particularly on the first run after some time for things to cool off. Figure some way to run a very straight line from one end to the other (lasers are great for that, but you can get away with a very tight chalk line, too) and then add or adjust hangers as needed to get the pipe equally straight. You'll be surprised how much "give" there is in a long piece of pipe.

tomsloancamp

@Jamie Hall whats the best way to hang and how to get the lift in the pipe?

Jamie Hall

Depends a lot on what's up there to hang it from. The simplest is just perforated metal strapping nailed or screwed into a joist overhead -- but there are a number of nifty pipe hangers which are easily adjustable to choose from. Even Lowes or Home Depot have some. A nice adjustable arrangement can be made with a clevis hanger, overhead threaded fitting, some threaded rod and a couple of nuts to match...

tomsloancamp

The problem has been solved..... the boiler needs to be skimmed. The oil from the new boiler was causing the hammering. And just in time for the cold weather! Now on to balancing the radiator.