What controls system pressure

bink

This is a basic question. What creates the system pressure I would think it is the water fill valve. My system gage shows about 18 psi. There is about 17 psi measured in the bladder expansion tank schrader valve.
I questioned the heating tech when he was here for another reason but he did not seem concerned. I have a split level home the highest level baseboard is less than 8-10 feet above the basement piping.
I keep reading that 12 psi is normal. Note sure if this higher pressure is ok.
My piping was done according to the schematics in the Pumping Away book I bought from heating help.
Thanks for your help.

j a_2

Very open ended question...post a picture then we will know if your installer is a real installer.....hope he wasn't a moonlighter

bink

J a Here are a few pictures. this was installed by a heating oil company seems the tech had reasonable knowledge but some things I question, it seems the techs want to rush the job so I never feel completely satisfied that they did the correct install.

j a_2

Step back and take a couple more

bink

a few more

4Johnpipe

The expansion tank cold fill pressure, fast fill and relief valve...

j a_2

Sorry pics lack clarity...step back and tak a pic of the whole boiler and piping the best u can...what I/we are looking for is a indication of what type of installer he is...Then we can comment...pressures vary with temp of water....normally static cold pressure is 12 psi..set originally by the fill valve....in a house like yours...FYI it's my belief that the fill valve should be closed at all times once the system is filled and rid of all air possible...think about this why would the fill valve have to add water after its full....where did the water go? Do u ride around with a hose attached to your cars radiator..lol

4Johnpipe

Here is a quick guide for setting pressure in a typical heating system.

4Johnpipe

The 12 PSI is normal to an extent. Measure from the top of your boiler to the 90 in the uppermost supply to a section of baseboard. If its 9' multiply by .43=3.87 PSI plus 4 PSI=7.87 PSI round to 8 unless you have a really cool gauge...

Zman

There is probably nothing wrong with 18 psi. Unless the expansion tank is undersized running 18 psi in a home that could run at 12 psi is not a huge deal.
In order to change your pressure to 12 psi you would want to remove and reduce the pressure in the expansion tank, then adjust the pressure reducing valve.

j a_2

Pressure reducing valve?n

Zman

j a said:

Pressure reducing valve?n

You know, the thing in the second picture with the lever on top and adjusting nut underneath?

bink

I will try to get a better picture. Thanks for reply's. I think they did a reasonable job of the install and the system works ok. Just wanted to know whether the higher pressure is ok.
Appears it has more pressure than needed but not urgent to correct

Zman

It is also possible that the valve and tank are set to 15. That is the factory preset.The tech may have increased the pressure manually. If that is the case it will eventually drop in it's own.

Gordy

Unless I'm mistaken that taco circ is not liking that orientation unless system pressure is over 20psi.

delta T

To answer your original question, static pressure in the system is created by the expansion tank, not the feeder. The feeder will add water if the pressure in the system drops below where it is set at, however when the pressure reaches the set-point on the feeder, the feeder is essentially closed and cannot actually supply pressure to the system. Hope that makes sense. The only pressure exerted comes from the compressed air in the expansion tank.

Was the pressure in the tank measured when the water side of the tank had no pressure on it? That is the only proper way to measure the pressure in the expansion tank. 12 psi would be considered standard by most for your system. If you want to adjust the pressure, first adjust the pressure in the tank to 12 psi, but only when there is no pressure on the water side (I usually remove the tank from the system entirely to do this), and then, once the tank is reconnected to the system, bring the static fill pressure according to your gauge up to 12 psi.

All this being said, Zman is dead on, 17 psi won't make a bit of difference to you system unless your expansion tank is really undersized which I sincerely doubt.

If you are concerned, watch what the pressure does as the boiler fires. If the pressure is still under 22-23 when the boiler reaches its maximum temperature and the burner shuts off, I would say you really have nothing to worry about. If it gets to 25, I would lower the pressure to prevent the relief valve from dripping and corroding. The relief valve will open at 30, but I have seen them start to very slowly drip at 27 or so.

There are differing views on whether the feed valve should be open or closed once the system is filled and purged. I won't hijack this thread with that discussion other than to say that if you do close the feed valve then your boiler MUST have a low water cutoff in order to prevent the boiler from firing dry assuming the system springs a leak.

@Gordy, I think you are right, seems like the pump motor is not horizontal? Hard to tell for sure from the pics.

JUGHNE

Aren't motor/pump shafts supposed to be mounted horizontally? Or not necessarily so.

delta T

Now I see the pic you guys are looking at. Pump is definitely vertical. to the OP, I would change the orientation of the pump unless you want to increase you pressure above 20. 20 is high for a residential system, as stated earlier 12 is 'standard'. your pump will last longer installed horizontally.

@JUGHNE, Taco says you can mount the motor vertically as shown in the pic (motor up) if and only if the static fill pressure is over 20 as Gordy said. Personally I never mount them anything except horiz.

Here is a link if you like:

http://www.taco-hvac.com/uploads/FileLibrary/102-054.pdf

4Johnpipe

Nice boiler...I noticed the temp was at about 165 the pressure will increase as the temp goes up...Definitely have them rotate the circ....

bink

Thanks I keep learning new info. I appreciate your posts. Very good to know about the tank providing the pressure I did not know that. Thanks delta t. Good to know about the motor position. My is vertical.

delta T

It looks like the pump flanges are rotating ones, which means it should only take a couple of minutes to rotate the pump to a horizontal position. Agree with John, I would definitely rotate it to make sure it lasts.

unclejohn

Maybe that's why he jacked the pressure up too 20# because of the pump.

nicholas bonham-carter

I think the pressure comes from the feeder, and the expansion tank is only reacting to that setting.--NBC

delta T

Well depends on how you look at it.

once the feeder has reached its set point, it acts somewhat like closed valve. Imagine you have a ball valve after the feeder. Once the system is filled, turn that valve off, and now the feeder is no longer a factor in the system.

Yes, it initially allowed water at a higher pressure (supplied by the municipality) to enter the system with enough pressure to overcome the push from the expansion tank, but now, once the system is full and the static pressure has reached the setting on the feeder (again imagine the closed valve) the only thing that is exerting any force on the un-compressible water in the system is the compressed air in the tank, no? Hence me stating that the expansion tank supplies the pressure.

rick in Alaska

delta T:
You got me confused on your explanation, but from what I am reading, I am going to say no way.
When you first fill a system, the fill valve will fill up the piping to what ever pressure it is set at, no matter what the expansion tank is set at. That pressure when everything is just sitting there, and before the boiler starts heating the water, is the static pressure.
But, in order for the expansion tank to do its job, which is to absorb any additional expansion from the water heating up, it needs to have its initial air charge set at the same as the fill valve pressure. I think of the expansion tank as a sort of shock absorber.
So no, it does not supply the pressure.
At least that is how I was always lead to believe.
Rick

j a_2

Zman said:

j a said:

Pressure reducing valve?n

You know, the thing in the second picture with the lever on top and adjusting nut underneath?

Zman said:

j a said:

Pressure reducing valve?n

You know, the thing in the second picture with the lever on top and adjusting nut underneath?

You do mean the pressure regulating valve...correct. Lol

j a_2

bink said:

This is a basic question. What creates the system pressure I would think it is the water fill valve. My system gage shows about 18 psi. There is about 17 psi measured in the bladder expansion tank schrader valve.
I questioned the heating tech when he was here for another reason but he did not seem concerned. I have a split level home the highest level baseboard is less than 8-10 feet above the basement piping.
I keep reading that 12 psi is normal. Note sure if this higher pressure is ok.
My piping was done according to the schematics in the Pumping Away book I bought from heating help.
Thanks for your help.

bink said:

This is a basic question. What creates the system pressure I would think it is the water fill valve. My system gage shows about 18 psi. There is about 17 psi measured in the bladder expansion tank schrader valve.
I questioned the heating tech when he was here for another reason but he did not seem concerned. I have a split level home the highest level baseboard is less than 8-10 feet above the basement piping.
I keep reading that 12 psi is normal. Note sure if this higher pressure is ok.
My piping was done according to the schematics in the Pumping Away book I bought from heating help.
Thanks for your help.

Take a look at the manual and read the min. Operating pressure I believe it is 15psig on that boiler...it also warns you of constant filling it's a good simple read.....I am not sure but most of them I thought had a built in low water cutoff.....the expansion tank is just that it has no control over system pressure...called by some the point of no pressure change,I agree....I suggest if that boiler was recently installed by a certified installer you look but no touch....but ask all the questions and expect answers from him...

bink

Thanks for all the good information. Just was curious about how the bladder type expansion tanks work. Good advise j a about not touching the system myself. I do rely on the techs to set this up which they have done. This site is a very good source of information.

j a_2

Yes I think it is very good....at times some of us disagree, but it's only that most of us posters are a wee bit old and set on our ways....Theroy is one aspect we can't disagree on, we prety much we're all taught by the best...at least I was...thanks to the wizard. Mr. Dan