Teledyne Laars Minitherm bypass question


  #41  
Old 02-24-10, 02:36 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
GREAT! good work.

Sometimes... you might get a few drop of water at first... maybe it's condensation from the air that gets put in... or maybe there's an itsy bitsy leak in the bladder... but this might get you through the heating season.

1. Isolating the boiler is fine... as long as the expansion tank isn't isolated by doing so. In other words, the expansion tank is on the boiler side of the isolation valves.

2. Yes, I doubt you will find a valve that closes opposite... the rule is "Righty Tighty, Lefty Loosey"

Keep an eye on the pressure next couple weeks to make sure everything is staying good...
 
  #42  
Old 02-24-10, 04:38 PM
F
Member
Thread Starter
Join Date: Jan 2010
Location: Canada
Posts: 39
Upvotes: 0
Received 0 Upvotes on 0 Posts
Both tank and boiler were isolated together. This will make installing a new tank easy, right?

So far so good. The pressure is stable at 18 psi during the day. It is 10-12 overnight when the boiler is mostly off, and it is 25 when the boiler is in overdrive in the morning to heat the house up.

Does this sound right?
 
  #43  
Old 02-24-10, 05:02 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
This will make installing a new tank easy, right?
Yeah, easier than having to drain the whole system!

Does this sound right?
Well... sorta... it IS marginal...

If you recall, early on in the thread I mentioned that the 30 size tank that you have might not be big enough for the volume of water in your system... LOTS of water in your system, and with that much water, you need more than the 'average' size expansion tank to give that water somewhere to expand to when it gets hot.

A little tutorial to help understand what's going on there:

When you take room temperature water, and heat it to 180, it expands a little under 4% in volume. So, say you have 50 gallons in your system (you probably don't have _that_ much, but it's an easy number to work with). When you heat that 50 gallons to 180 you now have 52 gallons!

You can not compress water, but you CAN compress air. When you heat that water up, that extra 2 gallons will flow into the expansion tank, and compress the air in the tank. This is how it controls the pressure.

With a marginally sized tank such as yours, it is BARELY large enough to keep the pressure under control. You have 13-15 PSI of pressure swing. This is taking the highest pressure very close to the opening pressure of your relief valve (30 PSI). It's recommended that the system pressure never gets closer than 10% of the relief valve pressure... so 27 PSI is the max you should ever have on your system... and the 25 that you have leaves very little room for error... you lose a little bit of air from the tank, and next thing you know, the relief valve is spewing.

If you can get through the winter the way it is, do so, but I would plan on going up to the next size tank in the spring.
 
  #44  
Old 02-24-10, 07:30 PM
F
Member
Thread Starter
Join Date: Jan 2010
Location: Canada
Posts: 39
Upvotes: 0
Received 0 Upvotes on 0 Posts
Should I drain some water to reduce the pressure a bit? I don't want to damage the system.
 
  #45  
Old 02-25-10, 12:33 PM
F
Member
Thread Starter
Join Date: Jan 2010
Location: Canada
Posts: 39
Upvotes: 0
Received 0 Upvotes on 0 Posts
Last night the pressure went down to 0 psi while the temp went below the guage min.


When things warmed up in the morning, the pressure rose (slowly) to 28psi, and the temp 150F.


Is this worrisome?
 
  #46  
Old 02-25-10, 03:42 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
Worrisome? yeah, I guess so...

It means that either the instructions weren't followed correctly, or your expansion tank is shot...
 
  #47  
Old 02-25-10, 08:41 PM
F
Member
Thread Starter
Join Date: Jan 2010
Location: Canada
Posts: 39
Upvotes: 0
Received 0 Upvotes on 0 Posts
The manual states:

"
Adjusting the bypass:
Starting with both balancing valves fully open, start the boiler. Adjust the balancing valve on the return to the system slowly to provide 120F (44C) water at the inlet to the boiler, leaving the bypass balancing valve fully open. As the system warms up, this valve may need to be adjusted open. In rare cases, this valve will have to be kept fully open, and the bypass balancing valve adjusted toward closed to prevent heated bypass water from satisfying the call for heat when the system is up to temperature.
"

I don't really understand this. Can you please explain what they are trying to say?

Thanks again, and sorry for my dumb questions.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: