Pressure drop when pump turns on

NovaScotia

So my house is zoned with pumps. (3)
And one main pump. I have an outside wood boiler so the system is separated with a plated exchanger. The main pump is located between the expansion tank and the hydronic manifold. The expansion tank is connected to an air micro bubbler and grind that is the pressure gauge.

When the pump is turned on I loose about 5/6 psi in the system. Any ideas?

Zman

Can you post a picture from farther back that shows the whole system?

NovaScotia

NovaScotia

Zm

Can you post a picture from farther back that shows the whole system?

I did

hot_rod

Does the pressure go back up when the pump is off. If so you are observing delta P
circulators move fluid by creating a pressure differential. A gauge on the pump discharge would??

NovaScotia

hot_rod said:

Does the pressure go back up when the pump is off. If so you are observing delta P
circulators move fluid by creating a pressure differential. A gauge on the pump discharge would??

Yes pressure goes back up when the pump is off. But correct me if I'm wrong I need at least 12psi for the zone pumps to work correctly for the second story zones. And considering the first floor is one pump going to 5 baseboards.

Wouldn't the pressure drop mean I have cavitation?

Zman

• Is your expansion tank properly charged to the system pressure? Does it sound waterlogged if you tap on it?
  
• Is there another expansion tank or something else in the system that may be acting like an expansion tank? Maybe a radiator with air in it?
  
• What is the system pressure with no circs running?
  
• Does the pressure vary depending on how many zone circs are operating?
  
• What happens when you vary the speed of the circs?
  

It's probably not worth repiping it but it would be better to have the expansion tank tapped into the hydro-sep with all circs pumping away from the hydro-sep.

Derheatmeister

In which direction are you "Pumping" ? Towards the Caleffi hydro seperator or away from it..
Is the Electric Waterheater your Heat source and is it only used for heating not DHW

psb75

He has an outdoor wood boiler.

Jamie Hall

I can't make head or tail of the piping. However, almost certainly what you are seeing is a pressure drop on the inlet side of the pump -- which means that whatever is stabilizing your system pressure is on the outlet side. You are correct in thinking that you need about 12 psi static pressure (actually, 15 would probably be better) to keep water in the second floor of the system. However, so long as that static pressure -- or more -- is maintained up there, you're fine. Now when you turn on a pump, it creates a pressure difference across the pump. That's what pumps do. It will either lower the pressure on the inlet side, or raise it on the outlet side.

It would be much better to have whatever is stabilizing the pressure on the inlet side of the pump. And I can't tell, as I say, how this thing is hooked up....

NovaScotia

Zman said:

• Is your expansion tank properly charged to the system pressure? Does it sound waterlogged if you tap on it?
• Is there another expansion tank or something else in the system that may be acting like an expansion tank? Maybe a radiator with air in it?
• What is the system pressure with no circs running?
• Does the pressure vary depending on how many zone circs are operating?
• What happens when you vary the speed of the circs?

It's probably not worth repiping it but it would be better to have the expansion tank tapped into the hydro-sep with all circs pumping away from the hydro-sep.

Pressure holds firm on 12psi with no pumps on.

Only the one expansion tank in picture.
It does not sound waterlogged.
 And I actually just figured out that my zone pumps won't push water up into the zones. So either the psi is dropping to low. Or maybe I have over sized my "main" pump?

NovaScotia

Jamie Hall said:

I can't make head or tail of the piping. However, almost certainly what you are seeing is a pressure drop on the inlet side of the pump -- which means that whatever is stabilizing your system pressure is on the outlet side. You are correct in thinking that you need about 12 psi static pressure (actually, 15 would probably be better) to keep water in the second floor of the system. However, so long as that static pressure -- or more -- is maintained up there, you're fine. Now when you turn on a pump, it creates a pressure difference across the pump. That's what pumps do. It will either lower the pressure on the inlet side, or raise it on the outlet side. It would be much better to have whatever is stabilizing the pressure on the inlet side of the pump. And I can't tell, as I say, how this thing is hooked up....

By inlet do you mean pumping away or towards the expansion tank?

Basically it is piped as follows.
Pump pushes water towards the Caleffi hydro seperator back around and through the heat exchanger. It then goes up to another heat exchanger for my DHW ( for on demand) and then back around through the y strainer and micro bubbler to the pump.

Now I was thinking that maybe I shouldn't have it go through both heat exchanger? I piped it this way to have a double protection so to speak from the outside wood boiler water(inhibitor).

However I have just found out that my zone pumps are not pushing water to the zones so either I have air hiding in the system or my "main pump" is over sized and the draw is to much for the other pumps to overcome?  Or the psi is to low?

Jamie Hall

Is there a possibility that you could draw a schematic of your system? Showing where all the pumps and the expansion tank and valves and so on are located and how they are connected?

You say that your zone pumps won't push water up into the zones. The water is already there -- there is no need to push it up (if it isn't there, you need more static pressure). What is needed is to make enough pressure difference to make it flow; that's what the pumps are for, and it only takes a few psi difference between the inlet of the pump and the outlet.

Anyway, with a schematic we might be able to come up with some intelligent comments...

NovaScotia

Yes that is what I meant by push. The water is there. The flow of the water is not going into the zones ” baseboards" I will draw one up

EdTheHeaterMan

NovaScotia said:

I actually just figured out that my zone pumps won't push water up into the zones. So either the psi is dropping to low. Or maybe I have over sized my "main" pump?

There is another possibility. Are the zone loop(s) air bound? You could have 50 PSI of static pressure and the circulator will not lift water any higher than the pump head pressure. You must not have any air in the loop.


The static pressure is the amount of pressure the entire system is subjected to. The air in the system and the water in the system are subject to the same pressure.

Additional information: If the gauge is placed at the bottom of a water column, the pressure gauge will read a higher pressure. If the gauge is placed at the top of column of water it will read a lower pressure. If the system is closed and charged to 5 PSI or 50 PSI but the air is still there, the amount of head pressure the pump will generate does not change. The water still weighs the same and the pump head pressure is also still the same.

NovaScotia

Jamie Hall said:

Is there a possibility that you could draw a schematic of your system? Showing where all the pumps and the expansion tank and valves and so on are located and how they are connected? You say that your zone pumps won't push water up into the zones. The water is already there -- there is no need to push it up (if it isn't there, you need more static pressure). What is needed is to make enough pressure difference to make it flow; that's what the pumps are for, and it only takes a few psi difference between the inlet of the pump and the outlet. Anyway, with a schematic we might be able to come up with some intelligent comments...

NovaScotia

EdTheHeaterMan said:

I actually just figured out that my zone pumps won't push water up into the zones. So either the psi is dropping to low. Or maybe I have over sized my "main" pump?

There is another possibility. Are the zone loop(s) air bound? You could have 50 PSI of static pressure and the circulator will not lift water any higher than the pump head pressure. You must not have any air in the loop.

Not quite sure I understand what you mean by air bound? It is a closed system. All the baseboards have bleeders that I have bleed.

Jamie Hall

And where, on that diagram, are you seeing the pressure drop? If it's at the inlet to the main circulating pump, either the expansion tank isn't working -- either waterlogged or overpressured -- or the valve between the tank connection and the pump inlet isn't open all the way (or there is some other significant restriction in the piping between the tank and the pump inlet).

mattmia2

Jamie Hall said:

And where, on that diagram, are you seeing the pressure drop? If it's at the inlet to the main circulating pump, either the expansion tank isn't working -- either waterlogged or overpressured -- or the valve between the tank connection and the pump inlet isn't open all the way (or there is some other significant restriction in the piping between the tank and the pump inlet).

Both those HX in series are a significant restriction. The DHW should probably be off of another zone off of the hydro separator with its own circulator for a number of reasons, but it should work this way assuming there is enough pump to move enough water through both HX, the outdoor boiler, and the interconnecting piping.


EDIT:

The "system" circulator is just the 2 HX and the system piping, but the gauge is on the suction side after both HX so it will be the point with the least pressure. If you measure the pressure in the hydraulic separator it will be higher. If the PRV was at the same point as the gauge it would bring the pressure up to 12psig, you could also manually bring the pressure up by opening the manual feed until you get 12 psig on that gauge. If there is a lot of water in the system you may need to adjust the air pressure in the expansion tank (with no pressure on the system side of it) to the new static pressure that gives you the 12psig dynamic pressure, but you don't need that as long as you have enough pressure to keep the circualtor from cavitating, you always have higher pressure in the heating loops.

NovaScotia

Jamie Hall said:

And where, on that diagram, are you seeing the pressure drop? If it's at the inlet to the main circulating pump, either the expansion tank isn't working -- either waterlogged or overpressured -- or the valve between the tank connection and the pump inlet isn't open all the way (or there is some other significant restriction in the piping between the tank and the pump inlet).

Oops the pressure gauge is located to the right of the air(micro bubbler)

 The expansion tank is new, and it is supposed to be pre charged to 12psi

I tested it and the guage said 15 psi for the expansion tank.

Edit:
I think it's also worth mentioning that the auto fill valve also has a pressure gauge for the supply water. That guage also shows loss of psi when pump is turned on

mattmia2

Hmm, the prv is at the tank on the suction side of the circulator. Is the prv and the supply to it open?

NovaScotia

mattmia2 said:

Hmm, the prv is at the tank on the suction side of the circulator. Is the prv and the supply to it open?

By prv do you mean pressure relief valve?

There is no water coming out of the relief valve.

The auto fill valve stays open and only fills up to set psi lvl.(12psi)

mattmia2

PRV = pressure reducing valve. It is what maintains the system pressure. If it and the gauge are at the same point it should be keeping the gauge at whatever it is set for if it is working and open.

mattmia2

Oh, I didn't notice that strainer until just now. Make sure that is clean too.(although it is not between the PRV and the circualtor or gauge, the PRV should still be keeping it at whatever pressure it is set for.)

NovaScotia

mattmia2 said:

PRV = pressure reducing valve. It is what maintains the system pressure. If it and the gauge are at the same point it should be keeping the gauge at whatever it is set for if it is working and open.

https://www.supplyhouse.com/Caleffi-553642A-1-2-NPT-AutoFill-Boiler-Feed-Valve-w-Pressure-Gauge?gclid=CjwKCAjwh5qLBhALEiwAioods97aopvt09HslnLqG-BxPJZJTuNcIfVYBTWkH-Jf4Od9WqxO-nInpxoCa_UQAvD_BwE

That is the only prv in the system and it's on the water feed. That guage also losses psi when pump turns on.

Should I have another prv in a different location?
Or is it possible that that prv is bad? That is also new.

mattmia2

Are you sure it is adjusted to 12psig? If you drain some water out with the system off, does it come back up to 12psig? My bet is no, either it comes up to some lower pressure or it doesn't come back up at all. Unless there is some valve or other device I don't see, the pressure at that point can't drop below the setpoint of the PRV if it is working correctly.

NovaScotia

I checked it last night. I will have to test that later. 

Am I right to assume that this pressure drop I am getting could also cause my zone pumps to not being able to move the water through the zones?

And is it possible that my main pump is simply over sized for the application and the flow/draw is causing the psi drop and my zone pumps are not big enough to overcome it to make water flow into the zones?

I have another taco 0018e I can swap with my main pump and test it. If it does not work I will test the prv. After that I don't know what to do other then re-pipe the other DHW HX to another pump and test.

What is the best way to test my expansion tank to see if it's good?

mattmia2

NovaScotia said:

Am I right to assume that this pressure drop I am getting could also cause my zone pumps to not being able to move the water through the zones?

No. They are air bound or the circulators aren't working or something else. If you measured the pressure at the hydraulic separator you would see it is more than 12psig. You are seeing a pressure drop at the gauges because they are after the outlet of both of the heat exchangers which likely are fairly restrictive (and possibly a clogged strainer).

The pressure between the circulator and the heat exchangers is lower and the pressure in the rest of the system is higher.

NovaScotia said:

And is it possible that my main pump is simply over sized for the application and the flow/draw is causing the psi drop and my zone pumps are not big enough to overcome it to make water flow into the zones?

No. That is the function of the hydraulic separator, to isolate the flow from one circualtor to the other.

If you haven't tested the PRV to make sure it brings the pressure back up if you let some water out, that is the first thing I would do.

Remember, the PRV can only let water in, it can't let it out so if it is set to say 5psig and it fills it to 5psig when the circulator is running the pressure at that point will come up to some higher pressure when the circulator stops if there is significant restriction in those heat exchangers.

I suspect that there is air in your heating loops somewhere and that is why the pressure is falling on the inlet instead of rising on the outlet.

How did you test the PRV before?

Jamie Hall

Let's go back to square one here. Close the valve between the expansion tank and the system. Drain the expansion tank. Set the air pressure in the tank to 12 psi. Now reconnect the tank to the system. Make absolutely certain that the valve between it and the system is open. Using the autofill, bring the system up to pressure (all pumps off) 15 psi. Make absolutely certain that the valve on the pipe between the expansion tank and the pump inlet is fully open.

Now start the pump. The pressure at the inlet side should hold between 12 and 15 psi, since there has been no volume change of the water. If there is more change, recheck the tank pressure (which should still be between 12 and 15 psi). If that's OK, look for the obstruction between the expansion tank and the pump inlet. If the expansion tank didn't hold pressure, there is a tank problem.

NovaScotia

mattmia2 said:. How did you test the PRV before?

I closed off the zones and set the prv to 25 psi to pressure test the system for leaks. It got to 25psi but that was with no pumps running.

So what you are saying is there is a air Pocket somewhere in the system. That air Pocket is causing back pressure which would explain my problems?

Edit:
Not with the pressure drop.that is because of the restrictions. I understand that.
But with the water not flowing through the zones

mattmia2

Actually, the pressure drop is because of the air, instead of pushing the water through the system, the circulator is compressing that air pocket wherever it is.

The fact that the pressure didn't come back up would indicate that you probably turned it down below 12psig when you were done. You used the slotted adjusting screw, not the big gray knob that is the valve that turns it on or off, right?

NovaScotia

mattmia2 said:

Actually, the pressure drop is because of the air, instead of pushing the water through the system, the circulator is compressing that air pocket wherever it is. The fact that the pressure didn't come back up would indicate that you probably turned it down below 12psig when you were done. You used the slotted adjusting screw, not the big gray knob that is the valve that turns it on or off, right?

Yes, the gray knob adjust the water flow. And screw on top adjust the psi limit

NovaScotia

Jamie Hall said:

Let's go back to square one here. Close the valve between the expansion tank and the system. Drain the expansion tank. Set the air pressure in the tank to 12 psi. Now reconnect the tank to the system. Make absolutely certain that the valve between it and the system is open. Using the autofill, bring the system up to pressure (all pumps off) 15 psi. Make absolutely certain that the valve on the pipe between the expansion tank and the pump inlet is fully open. Now start the pump. The pressure at the inlet side should hold between 12 and 15 psi, since there has been no volume change of the water. If there is more change, recheck the tank pressure (which should still be between 12 and 15 psi). If that's OK, look for the obstruction between the expansion tank and the pump inlet. If the expansion tank didn't hold pressure, there is a tank problem.

Just to clarify yo are saying to close off expansion tank and just let the water out? Or let water and release and pressure tank has till it's empty. Then re-pressure tank

mattmia2

You have to isolate the expansion tank so that there is no pressure on the water side (it should be empty at this point if it is charged) then pressurize the air side to the cold fill pressure of the system, in this case 12psig. The water side should be free to expel any water that is still in it when you pressurize the air side and the water side should remain at atmospheric pressure.

mattmia2

I just thought of something else, if the outlet of those heat exchangers is at the bottom rather than the top they could be difficult to purge of air depending on the velocity the circulator produces in that loop.

Does that loop get nearly as hot as the loop from the boiler? Does the pressure still drop in that loop if you open the bypass and isolate the heat exchangers? What about if you isolate the heating loops? If you close all of the isolation valves (and open the bypasses for the heat exchangers) the pressure should stay about the same when you start the circulator. You can then open sections one at a time and see when the pressure drops, this will tell you where the air is.

Essentially the air in some section of the system is acting the same as if the expansion tank were on the outlet of the circulator.

EBEBRATT-Ed

@NovaScotia

Where the expansion tank is connected to the system is the "point of no pressure change". In reality the pressure will change a couple of psi

If you want 15psi at the pump suction make sure the expansion tank has 15psi on the air side. You have to remove the water pressure on the ex tank to do this. Your water feeder has to be set to 15psi as well.

You have a few fittings between the ex tank and the pump which will give you a little variation.

Most systems I have seen when the pump comes on the suction pressure will drop a couple of psi while the expansion tank and feeder adjust.

Just adjust the feeder pressure up a couple of psi and when the pump is off you will have 17-18 psi.

That is normal.

The other possibility is that you have some air trapped in the system so the pump thinks it has two expansion tanks so bleed the system

NovaScotia

Jamie Hall and Mattmia2 thank you both so very much. Words cannot express the relief,and weight off my shoulders. 
I drained the first floor zone. I had one Run from zone 3 that went to the baseboard and came back down into the basement into another baseboard to get a little extra heat on that side. Only it had no bleeder. Only the one on the first floor did. But it was one loop. I cut that out and ran it right back to the manifold from the first floor baseboard. 

Redid the expansion tank and got the 2 gauges and the expansion tank within 2 psi of each other. between 12-15psi. Refilled the system and bleed the **** of the baseboards. 

Turned on main pump and I only lost about 1, 1 1/2 psi.
Turned on zone 3 pump and hear air moving around. Re-bleed baseboards again and it bloody works! Just gotta tweak the 0018e to get the flow I want.

Thank you again. my family won't get cold tonight

Zman

This is a very good thread. It is a tribute to @DanHolohan 's ability to help so many people visualize the PONPC and it's effect on a system

mattmia2

If you can figure out a way to open and close valves such that you can force water from the prv through one loop at a time and out a drain you should be able to purge those loops well enough to get them flowing without a bleeder, then the microbubble scrubber can remove the remaining air as the water circulates through it. That was likely how it was purged originally.

pecmsg

NovaScotia said:

Jamie Hall and Mattmia2 thank you both so very much. Words cannot express the relief,and weight off my shoulders. 
I drained the first floor zone. I had one Run from zone 3 that went to the baseboard and came back down into the basement into another baseboard to get a little extra heat on that side. Only it had no bleeder. Only the one on the first floor did. But it was one loop. I cut that out and ran it right back to the manifold from the first floor baseboard. 

Redid the expansion tank and got the 2 gauges and the expansion tank within 2 psi of each other. between 12-15psi. Refilled the system and bleed the **** of the baseboards. 

Turned on main pump and I only lost about 1, 1 1/2 psi.
Turned on zone 3 pump and hear air moving around. Re-bleed baseboards again and it bloody works! Just gotta tweak the 0018e to get the flow I want.

Thank you again. my family won't get cold tonight

So the kids get 2 pints of Ice Cream Tonight!

Its fun being a grandfather.