Posted by Tony Conner, TBP Industrial Steam Systems on December 28, 1997 at 11:30:40:
In Reply to: Re: New boiler system over-pressure posted by dale van aken on December 28, 1997 at 05:40:22:
: Thanks for you ideas, Joe. This is a new house - all the piping is 3/4 copper. The water supply is a well set at 30-50#. When I looked at the Amtrol literature, they suggest the Model 60 for 150,000 to 250,000 BTU. Since I am well in this range, it seems to be sized right. Also, the HW tank is always at temparature (it may change a few degrees or so, but when I stabilize the system, it should not increase its temp much to create thermal expansion. I am wondering if the large circs (Taco 009 and 011) could be creatins short pockets of low pressure on their intake side when they kick on, especially the heating, since it is feeding only a 3/4 pipe and would have some resistance on its pressure side. With short pockets of low pressure, it would allow the watts pressure valve to slip in more and more cold water, eventually too much. Sound plausible?
Dale: When you say 3/4" pipe, do you mean just the domestic water supply piping, or your heating pipe as well? Your heating loop should be at least 1-1/4" (1-1/2", really)to supply 150,000 BTU/hr. 3/4" copper pipe in a heating loop will only handle about 4 GPM, or 40,000 BTU. Check the location of the make-up water connection. It should be in the section of pipe between the main loop and the expansion tank. If the make-up valve is located such that the pump suction can affect it, it is in the wrong place. For the best operation and air removal, the circ pump should be on the outlet side of the boiler. The air separator is located between the boiler and the pump, along with the expansion tank. The expansion tank is known as the "point of no pressure change", and rules where the pressure drops occur in the system. Having these drops in the wrong places causes all kinds of weird problems with make-up water and air pockets showing up in rads. Check Dan Holohan's book "Pumping Away" for an excellent explaination of this. Tony