pressure drop during boiler operation

Paul Mitchell_2

like the location of the reducing valve is in the wrong position. This will feed if not in the position of no pressure differential. That being said Is the relief blowing because of temp or psi.? If it is temp then there might be a malfunctioning control. But I would definately move the feeder placement. If you can actually see the gauge drop. Also a slight chance of too much pump for the system. A picture would help. Depending on the piping design of the new system you may need a bypass loop but not to help this problem. Turning off the reducing valve is procedure according to some manufacturers after system is filled to pressure. The reality is one night to see if problem persists should not be a problem but with no low water cut off there is always a slight risk. In NJ the code requires a lwco on all boilers. Not sure of your location but it is a good practice anyway.

john_74

boiler pressure droping during operation

I have a system that was recently installed. All components of the system were replaced. (ie boiler, exp. tank, fill trim, pump) The situation is that the relief lifts occasionally. The diagnosis for the problem was that the pump is pumping away from the boiler to rapidly and drawing in water from the fill. The pressure gauge does drop on start of pump! The pump is a Grundfos UP26-64, the boiler has a 160,000 btu input, and lifts approxiamtely 25'. The home is approxiamtely 2800 square feet. Then once the boiler heats up the relief lifts at temperature. The home is a older home with large existing piping system (3"mains). Would a "by-pass" loop solve this problem? And is it safe for the technician working on it to shut the water off and leave to "just see if that takes care of it."????? The boiler is not protected with L.W.C.O. and with a lifting relief valve by having the water shut off is this even safe or a reasonable practice???

Paul Mitchell_2

Response to e-mail

Ok so since the reducing valve has been off has tings been good. If so then I think it is just pump location? maybe. Just a rough idea is off the top of the boiler you should have piping to a air scoop of some sort. The reducing valve is in at the bottom of the scoop and then the extrol off that. After the scoop then the pump. Maybe the extrol is undersized? I would also call the manufacturer if the company that installed it is having trouble. You should continue to post this on the wall you could get some more responses. I am going to also copy this response on there so the other guys can see.

big bob

pressure problem

what size is the extrol tank.if it is a new install on an old house and it has the larger old piping.then i would have to lean towards the extrol tank being undersized.the only reason i say this is because with piping that size i'm pretty sure the new grundfos would not carry that much more head pressure than the old circ{probably a b&g i would guess.}just a thought i have been in the business for only a few years but have seen it happen a few times.i don't have the experience most of the guys on this sight do but i am trying to make resonable sense of the info you gave.hope it helps.

Sweet_2

Expansion tank

I wouldnt have any problem using 26-64 on that size system I use them on smaller systems as well its not a small pump but its not going to develop enuogh head to do this. Also you wouldnt want to pump towards the exp tank in my opinion I know alot of people dont see the benefit of pumping away. I understand I use to do it to. But I see the real difference now air stops being a problem. Id look to overpressurization of tank or saturation of tank.

Empire_2

Also keep in mind that since you are pumping into a 3" main the valocity of your water will drop substancially from the 11/4" or 11/2" piping that the boiler was pipped with. The water will move very slow at a 3" main. Also the pump in this case does not lift water at all. With the fill valve off, if the relief is still popping, then it is your expansion tank. If not popping then your fill valve has some debrise in it which is not shutting down incomming water to boiler.

Empire_2

Information.

I also have to say that Obtaining Information on pump curves at the Grundfos web sight is a Joke. I guess That is why I prefer B&G Where the Info is easily obtained!!!

Sweet_2

I agree its

a bit of work to get them. Taco has made them pretty easy also.

[Deleted User]

What is your fill pressure ? You say you are lifting 25' is that the height of the house. What's your pressure on the top floor? 12 psi may or may not be the right fill pressure. Also check the air pressure in the expansion tank with the tank isolated and the water side drained. Your expansion tank air pressure should match the water pressure you need to overcome the building height