York Shipley steam boiler flooding on shut down

SethYank

Yesterday I looked at an older York Shipley steam boiler that was installed in a commercial bakery with a large building. It is no longer a bakery so whatever equipment that was attached is gone, it is now used for heating the building only. They fire it up about 6am and shut it down about 6pm. It is set to run about 2 psi. It has an automated bottom blowdown system that blows down 3 time a day, supposedly the automatic valve was torn apart and cleaned by another contractor (this problem has been going on for a while and they asked me to look at the system.) There are supposedly radiators and pipe radiators upstairs and modine steam heaters. No I did not get the time to go over the entire system hand over hand. There are two condensate storage tanks, one in the basement receiving condensate from first floor and basement piping and the main tank in the boiler room. Both tanks are about 50 gallons. The basement tank pumps up to the return piping to the boiler room tank. When I arrived every time the basement tank pumped up, the boiler room tank overflowed. The sight glass valves were plugged, I cleaned them and replaced the taco 12 psi reducing valve that had been installed before the McDonnel float valve on the end of the boiler room tank which had supposedly also been rebuilt,(they had all but shut the ball valve in front of the reducing valve to "control the pressure." The boiler room tank sits about 2-3 feet above the boiler water line and has a pump that is actuated by a McDonnel miller float switch on the boiler. The pump discharges to the boiler thru a spring loaded check valve ( the seats and spring pressure look ok inside it) then a swing check(did not open this one.)
There are some bellies in the piping in the basement I pointed out to the owner. Also there are steam traps at main ends, modines, and one off the main header returning to the feed tank, I believe this one is working because I am not getting steam out of the vent of the tank.
So I replaced the pressure reducing valve to feed the tank and it still flooded this morning, my next step will be to verify the float valve on the tank is actually working, the water level in the tank is 1/2 way where I left it yesterday. The other thing that just came to me is when shutdown the condensate in the upper level is draining back thru the steam piping and filling the boiler,?.

1-9-19
Yes , your assessment of the condensate tanks is correct, but the owners and renters are nursing this boiler on a shoestring so I doubt I am going to convince them to make the necessary changes, they will let the overflow go into the drain. They are currently doing the 3 blowdowns to get rid of water because of the flooding.
I checked the system out further last night, The majority of the heat appliances have traps on them. The boiler cycles on the pressuretrols, on at 1 psi and off at 4 psi. I shut the burner down and watched the boiler and boiler condensate tank. As the pressure in the boiler hit zero, I saw the boiler level go up. There was no sound of water coming back thru the supply piping ( the boiler room is very quiet when shutdown and there are a lot of vertical pipes in the supply piping.) The condensate tank also showed a slight drop in level with the burner off, the condensate returning to the tank should have made it go up.So I am thinking the boiler is going into a vacuum and sucking the condensate in thru the feed system. I am going to install a vacuum breaker, I was planning to install it on the control piping on top of the boiler. This will admit air to the boiler. If I install it on the feed pump discharge this will also admit air to the boiler thru the feed piping. Admitting air to the boiler means It will have to clear thru the steam piping and thru the traps, Which considereing the number of leaks in the system wont be a major problem.

Something else I am thinking about for this boiler is reducing the system pressure since there is no equipment requiring 2 psi. And I am thinking about trying to downfire the powerflame burner. Both of these ideas are to try and lengthen the run time of the boiler to maintain a steady flow of steam to the heaters. With the long runs of piping and considering some have sags in them should I take the pressure cut in down to 1/2 psi and my cutout up to 2 psi. And any one have input on the down firing. I realize I have to be able to put in enough btu's to create the steam I need. Help appreciated.

Jamie Hall

Have I got this straight? The basement tank receives a good bit of condensate, and has a pump to the boiler room tank. That pump is controlled by the level in the basement tank? (That's a critical point). Then the boiler room tank has a fresh water feed controlled by a float valve on that tank, and receives condensate by gravity, and has a pump to the boiler controlled by the boiler.

That right?

If that's the way it's hooked up, then consider: the float valve in the boiler room tank has no way of knowing when the basement tank is going to pump So... it senses low water in the boiler room tank and brings the level to where it belongs. At some point, then, the basement tank fills to the point where its pump turns on -- and the boiler room tank promptly floods -- since the basement pump has equally no way of knowing when the boiler room tank needs water.

Seems to me that what needs to happen is that pump in the basement tank needs to be controlled by a float in the boiler room tank, which asks the basement tank pump for water before the fresh water feed kicks on but when the boiler tank is a little low. There would still need to be a float in the basement tank which turned the basement tank pump off at a very low level. Then your primary source for the boiler tank would be the basement tank, and only if that basement tank were empty would you get a fresh water feed.

Would you then get overflow from the basement tank instead? Quite possible -- so provision should be made for that -- but I rather suspect not.

What do you think?

I'm not convinced of the need for a three times a day blowdown. You do need that for process, consumptive steam, which this probably was when the bakery equipment was still in there -- but if there is no consumptive use it might be better to reduce the frequency of that blowdown.

JUGHNE

Does the boiler go into a vacuum on shutdown?
Others have had this problem of syphoning water into the boiler from tanks or heat exchangers.
IIRC a vac breaker or check valve to atmosphere stops the problem.

EBEBRATT-Ed

What @jughne said.

With the boiler feed tank above the boiler you are likely getting a sylphon into the boiler. without seeing the piping it is hard to say but a vacuum breaker and check valve can fix this.

One way is to come off the boiler feed pump and run the feed water pipe above the boiler water line several feet. Put a vacuum breaker at the top of this line on a tee and drop down and feed the boiler.