What would be correct flow switch for our application?

Dave_118

Currently we have a McDonnell and Miller FS8 flowswitch in our system but may need to replace it. The switch is installed in a 2" brass tee that has a threaded leg in it. The switch is screwed into the threaded part of the tee, and then the tee was soldered into our 2" copper boiler circuit. We are running a Taco 0010 pump in this boiler circuit which circulates between our Ergomax tank and our gas boiler.
We have had several lockouts on our boiler, and it seems that the flowswitch is intermittently not making contact. On reading the info for the switch, it is not recommended for our application due to the fact that the paddle does not extend far enough into the flow in 2" pipe. And a longer paddle would contact the side of the tee.
Does anyone out there know of a flowswitch that I could replace this with without doing any repiping?
Our flow is most likely about 25-30 gpm of a glycol/water mix.
Thanks.
Dave

Unknown

They can be problematic

if the paddle is not stiff enough,,when you say "2" brass tee that has a threaded leg in it" do you mean the side branch of the tee is tapped like a DWV line cleanout?
If you are getting the flow, there is a sensitivity adjustment.


Dave

Dave_118

Yes, I believe so...

the tee is brass and the 2 ends are 2" and are soldered to the 2 " copper pipe. The tee portion is threaded and I want to say is 3/4" for the flowswitch to thread directly into it.

Glenn Sossin_2

I would check your flow rates. The Taco 0010 is a low flat curve, not alot of head. Depending on pipe size and length, I would think you should have a Taco

Plumdog_2

fine tuning needed

You can "stack" the paddles, with the large one facing the flow (looking upstream) and a couple smaller ones in back to stiffen the assembly. Then trim off the excess until the thing travels smoothly and trips the switch easily. It is best to do this before the Tee is installed; so you can look in and SEE what's happening. But you might just adjust the sensitivity and get it working.

Glenn Sossin_2

I would check your flow rates. The Taco 0010 is a low flat curve, not alot of head. Depending on pipe size and length, I would think you should have a Taco

Glenn Sossin_2

Pipe size larger than necessary?

Why such a large pipe with such a relatively low flow? It would seem 11/4 of 11/2 could be adequate and thereby potentially eliminating the switch problem.

hvacfreak

Omega

I used a sealed unit made by someone called " Omega " recently. I'll try to get a link...I think they make process controllers and such. This valve was only 3/4" , but i'm sure they have other sizes.

Dave_118

Well,

unfortunately, that horse is out of the barn. But this system has run for over a year without any problems. The flow is 25-30 gpm. I would think that would be more than adequate in a 2" pipe to rip the switch. I am wondering about one of these other switches that are not mechanical. Would the Omega work for this application? I was looking on their website. The tee where it would be inserted into the pipe is situated vertically (directly at 12:00). Would that be an issue?

hvacfreak

link

http://www.omega.com/ppt/pptsc.asp?ref=FSW30&Nav=greb09

This is what I was using. Seemed like a quality piece.

edit ...and this

http://www.omega.com/toc_asp/subsectionSC.asp?subsection=B09&book=Green

Dave Stroman

I use flow switches on every low mass boiler I install. Over time the sensitivity of them can become a problem. There is some adjustment on the switch but I have learned that I need to use as long of paddle as I can, I need to use a smaller pipe size in the area of the switch, and/or I need to simply over pump the system. You could try to change out the pump with one of the Grunfos 2699 3 speed pumps. Dial in the the speed that give good switch operation.

Dave in Denver

Dave_118

Dave,

I turned on the boiler with the flow switch connected and then slowly backed off on the screw until the switch made contact, and the boiler fired. Then I backed off a little more to give us some fudge room. If this recurs, I may have to switch out the switch or the pump.
If there were any flow problem ( if the switch were not defective), wouldn't I expect the delta T across the heat exchanger to be higher than its normal 20 deg? Or the boiler would make noise like it used to? None of these things are occurring.

LarryC

How much current is flowing thru the switch?

How much current is flowing thru the switch contacts when they are closed?

Some switches require a certain amount of current to make sure the opening arc burns thru the surface oxides when the contacts open up. If the current is greater than 50 mA, you should be OK. If it is less than 10 mA, I would contact the manufacturer of the switch to verify that is enough.

tim smith

flow switch

Make sure after adjusting to get it to turn on that you valve boiler off while running and make sure it will turn off boiler. I usually disconnect main valve so I don't have as much fire under boiler but still can hear the solenoid shut when I valve off. Triple check the on and off cycles otherwise you may have nuisance shut downs. Good luck, Tim

Dave_118

Thanks Tim,

I actually disconnected the power to primary pump with the boiler operating, and the boiler shut off instantly. I ran it through several cycles, and everything appears normal.