pressure needle on boiler inlet oscillates

Dave_61

gauge does the same thing.

Dave_61

pressure needle on boiler inlet oscillates

I had the copper tube boiler that was making the vibration (sounded like a truck running) a couple of weeks ago.
The T&P gauge on the inlet was defective, so I replaced it, and the vibration/rumbling has stopped.
However, I have noticed that the needle on the pressure gauge oscillates when the gas burner is on. If both stages of the burner are on, the needle oscillates wildly between 0 and 40 psi (running pressure with system hot is 25 psi) and makes a rapid ticking sound.. If only one stage of the burner is on, inlet needle vibrates between 20-25 psi.
The DDT across the heat exchanger is well within specs (max is 40). Ours is 20-25 with both burners on, and 10 DDT with single stage on, which means we have plenty of flow.
We are running a 30% glycol mix.
I'm fine with the way it is running now as long as we are not heading for a bigger problem down the road.
Thanks.
Dave

Jerry_15

It's shot. replace it.

Jerry_15

Replacing the gauge was just assuming that it was damaged by the real problem, which you now have to figger out. Sorry bout that, I usually throw a test gauge on some handy hose bibb. Now you have to run the gamut, ex tank delta t on flow (pump problems), gas manifold pressure,and what you will probably wind up with on a cop tube is some nastiness in the heat exchanger, which Mark Eatherton has addressed very nicely in one of the recent threads. Cop tubes are not very forgiving. That's about as diplomatic as I can be. I work on them, a lot: I do not install them anymore. Good luck.

[Deleted User]

You're seeing the same thing you saw before minus the noise...

and as I warned you, the wolves/whales WILL come back.

Have you used the chelates yet?

You are seeing micro bubble steam flash occuring at the tube/fluid interface. It happens because glycol retards the rapid flow of heat from the hot heat exchanger surface into the fluid. THe heat JUMPS into the fluid, causing a minut steam bubble to occur, then collapse, which is the vibration/oscillation you are seeing.

ME

Dave_61

Mark,

I will buy some and put it in the system.
I have been hesitant to do it because of the article that Drew from Noble produced saying the chelants were harmful if used longterm.

[Deleted User]

Dave

I don't make this stuff, I just use it, and the instructions that come on the stuff we buy (Dennis Bellanti's special boiler juice) says it's supposed to stay in the system. I don't dispute what Drew L says, but the manufacturers of this stuff HAVE to know how to use it.

In a "pure" undilluted form, there may very well be issues, but this stuff is blended and I've not had ANY problems with the product.

ME

Dave_61

Thanks Mark

I spoke with Dennis. He actually will be able to ship me some. Hopefully that will solve the issue.