Fill Valve Location Pressures

Chuck_20

Attached is a pdf sketch of a boiler system we recently looked at for a client. The fill valve is connected to hot side of the boiler just prior to the bypass valve for the indirect. The fill valve and the expansion tank are both set at 15psi. Our tech didn't check to see whether the boiler pumps were pumping in or away from the boiler.

My question is what happens to the pressures in the system with the fill valve in that position? 

What happens when the indirect calls and the bypass valve energizes

What potential problems could occur?



  

Brad White

Question

When the 3-way valve is in heating mode, there is a tee to the right of that in the diagram that seems to be a return connection. Is that a form of Primary/Secondary? It does not seem that it would work that way, just trying to get my head around it.



That said, the NPCW connection point will not affect the system pressure, it is the expansion tank point that does that. From what I see and assuming the circulators are pumping away, that is ideal. The NPCW connection only comes into play when you have a leak. That is what I see, anyway.

Mark Eatherton

Whatsa NPCW ???

A new Bradism?



Non pressurized cold water?



Non potable cold water?



Naturally protected chicken water?





Still learning.:-)



ME

Brad White

NPCW =

Non Potable Cold (or City) Water!



No Bradisms here. At least not right now. NPCW is nomenclature we have used for years, or at least my plumbing engineers insist that I use it.



Still learning here, my friend. May that never stop!



B.

Mark Eatherton

Gotcha...

The ONLY time I've seen the make up connection cause issues was a situation where the make up was connected to a high head circulators inlet. The pump was pushing against a high pressure drop mini tube circuit and was pumping towards teh Point Of No Pressure Change (PONPC).



Every time the pump would turn on, the pressure reducing valve would "see" a significant drop in pressure, and start feeding water into the system. Eventually, the 30# relief valve would kick in and drop the pressure and start the vicious circle all over again.



The simplest solution would be to have the NPCW connected at the PONPC.



Need some salt and pepper for your alphabet soup? :-)



By the way, what caused the potable water to become non potable? Before it hits the BFP, it was potable, no?



Thanks for the clarification Brad.



ME

Brad White

Potable? Non!

Well, fair point, the water was potable before the BFP but of course once isolated, the water is up for grabs by any system connected to it. It is likely still drinkable, but is outside the system so we take a pass.



Agreed a high head circulator might do that, so the PONPC gets the nod. Personally, I like no city water connection. Avoid the infinite leak.

Chuck_20

Primary - Secondary

It's a Primary -Secondary system. The pumps P-1, P-2, & P-3 feed baseboard radiators.  

Brad White

That valve and tee

arrangement, with two intervening tees, if installed as diagrammed, will defeat P/S and force flow between the circuits, FYI. Not the focus of your question, but for performance sake, can that be corrected? That is what I see, anyway.



But if you move your make-up water connection to near the air separator and expansion tank, that is a "best practice".

icesailor

PRV Location on sketch:

I know that you didn't didn't install this but why the fixation on putting PRV's on the supply side of a system AFTER the boiler?

I never saw a PRV installed anywhere else but into the bottom or return of a boiler until the late 70's or early 80's when they started showing them on Amtrols. Everything I do is set up on being able to purge the system. I have a lot of systems that I drain annually and turn back on in the Spring. Most and myself will set the whole thing up so I can purge the whole system when it is running, from one place. Because you are sending hot water into the system during the purge, you are replacing it with cold water, being heated by the boiler. An isolation valve on the return and a drain above it, the water runs cold, then runs colder, then warms and gets hot. It's purged. Open the valve and it continues to get hot.

I fill anti-freeze the same way. Pump into the bottom of the boiler and return into a 5 gallon bucket with the pump suction into the bucket. When the bubbles stop, open the valve. if the hot return doesn't start getting hot, purge some more until it starts to warm. When it is getting hot, on to the next zone.

You show no drains in your drawing and the boilers are all piped backwards which may have a reason. I just never would have put the PRV on the supply like that because it makes it so hard for me to purge. And if it was on the return, you wouldn't have a need to ask your question about the location.

Chuck_20

Pressure Question

I agree on the best practices and that's why this location is confusing to me.

If the fill valve is set to 15 psi and Boiler #1 starts and has an increase in pressure, does that add to the 15 psi and affect the expansion tank pressure of 15psi possibly making my expansion tank too small?

Note: The drawing doesn't show the additional valves for filling and draining

Chuck

Mark Eatherton

Doesn't matter...

Any slight increase in pressure created by the boilers heating water is going to be dispensed through out the system so quickly that it won't make any difference.



THE most important point is that ALL pumps should pump away from the expansion tanks connection to the system (PONPC). This way, they will all provide positive pressures to their respective piping/distribution systems, keeping bubbles small and avoiding potential steam flash due to cavitation.



There are a lot of better ways of being able to pipe this system, and increase overall performance, but it sounds like the deed is done already...



Are you currently experiencing system over pressure and relief valve action?



ME

Chuck_20

Relief Valves and Air Vents

The client had problems with a couple of the relief valves weeping. It came down to a bad expansion tank. We questioned whether the relief valves always had a problem, but the maintenance person didn't know because he is new to the facility.

We also questioned whether the expansion tank was sized right but he didn't have any of the existing plans for us to calculate the water volume. We thought it was borderline and he said to install the next size larger tank.

Recently the Air vent on the indirect water heater was leaking and then they also found that the AAV on the boilers were closed.  This could of been just maintenance, but that's why I'm questioning the pressures in the system and how things/locations of items effect them.

Again we're new to this system and don't know all of the history. We definitely would of piped it differently.

Chuck



  

icesailor

AAV's, PRelief Valves, PRV's:

I leave the AAV's closed after venting now. When they leak, I closed them. If open and the Extrol tank is bad, they suck air. If they are way above the boiler (second floor), they will suck air if the PRV doesn't maintain pressure and the Extrol tank is bad or undersized. IMO, better an over sized Extrol than an undersized one.

I find leaking 30# relief valves an indicator of a flooded expansion tank or an undersized Extrol tank. Whenever I find a leaking relief valve, after changing it, I always check the Extrol tank pressure. If it is at 12# or above, I think the Extrol tank is too small. If it is below 10#, I add air with the thought I may be back. If it is significantly below 10#, like 5#, I replace the tank. If 0#, I definitely replace the tank.

Jean-David Beyer

why the fixation on putting PRV's on the supply side

Since I am not a contractor, I do not know. But it is not just the contractors.



Weil-McLain show it there in their installation manuals for their Ultra 3 boilers, before any valves or anything that would "protect" it from the boiler pressure. John Siegenthaler shows them connected directly to the boiler.



From Pascal's Law in high school physics, the static pressure would be the same throughout the system would be the same, so you could put the pressure relief valve anywhere. But it is imperative that the pressure relief valve be placed where the dynamic pressure is the same as that of the boiler, and where the flow resistance between the boiler and the valve is minimum. And that means, the nearer to the boiler, the better.



I do not know the plumbing codes, but they probably insist the PRV valve be connected extremely close to the boiler. I see no reason not to connect it to either side, but I am not licensed to do anything. In my system the LWCO is the last thing before the return to my boiler, and the PRV is the first thing on the way from the boiler to the rest of the system.

Slimpickins

PRV

Icesailor is talking about pressure reducing valve or fill valve, not pressure relief valves. I know, kinda confusing. The best and ideal place for the make up water is to cap it before the tee going in boiler #1 and tie it in on the line going to the expansion tank 

icesailor

PRV Fill Valves:

Slim,

I was once filling a boiler and trying to purge it. A simple job. The fill valve was at the Extrol like you like. I purged and purged and never got any warm or hot water back. Because the boiler had been there for a few years, I expected that there would be no problems. What was happening though was that the PRV wasn't filling the boiler, just the system. The boiler had very little water in it, mostly air. The boiler wasn't piped properly for air elimination. It wasn't something you would notice. The boiler was at the same level as the radiation. It had been dropped in a hole in a floor and stuck up above the floor.

Purging a system is a whole lot easier when feeding the boiler at the bottom. And when purging with the boiler running, the burner is never going to be able to heat the water as fast as it comes in. Feed it on the supply and into the system and you don't cool the boiler and system.

Although this boiler was more or less piped correctly for having the radiation at or below the boiler, it could, and did fill the system and not the boiler first. If you have a flow check or zone valve on the supply, the water must go against the flow and fill the system first. I just don't like that. But, I guess I'm in the minority. I fill and purge a lot of boilers in a year. It sure is easy to purge them when you fill the boiler at the bottom. I don't see many boilers piped like you suggest so although I may be in your minority, where I work, it is common practice to put them on the bottom. And I've never EVER, EVER, EVER seen a problem doing it like that, EVER.

I have seen three boilers lunch and crack when they were filled on the supply at the Extrol when radiation or mains froze and broke and the water filled the system and never got back to the boiler. The water boiled out and then cracked. The flow check couldn't let water flow back into the boiler.